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1 MOVEMENT PATTERNS AND THE RELATIVE IMPORTANCE OF CONS T R UCTED AND NATURAL WETLANDS TO GREAT EGRETS IN THE SOUTHEASTERN U.S. By JASON C. FIDORRA A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTI AL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 201 2
2 201 2 Jason C. Fidorra
3 To my parents for everything
4 ACKNOWLEDGMENTS I thank the staff at Biodiversity Research Institute who provided lo gistical support during this project, particularly David Evers for getting things off the ground and his guidance throughout the project. I thank Ken Meyer and his crew at Avian Research and Conservation Institute who were responsible for the capture of th e great egrets in this study. I thank my advisor and committee chair, Peter Frederick, for his guidance, patience, and calming demeanor f or which I was continuously grateful. I thank my committee members, Kathryn Sieving and Robert McCleery for their sugg estions and editorial help. I am indebted to the many individuals who shared their knowledge of agricultural practices and bird behavior with me including : Jay Huner; Ray McClain, Robert Romaire, and John Saichuk from the LSU Agricultural Center ; Jeff Dura nd of Durand Farms; Sammy King and Brad Pickens of the USGS L A Cooperative Fish and Wildlife Research Unit ; Clint Jeske of the National Wetlands Institute ; and Christi ne Hand and James Rader from SC Dept. of Natural Resources I thank my technicians, Angel a Mulligan and Dylan Scott for their assistance in the GIS lab, and Mary Grace Lemon for her help with a e ri al surveys. I also thank Charlie Hammonds for keeping Mary and I safe while piloting my survey routes. I am grateful for the wonderful staff at the U F Wildlife Conservation and Ecology Department, and my lab mates Brittany Burtner and Louise Venne, wh o not only provided suggestions but also distractions from my work which were necessary to maintain my sanity. Above all, I thank my parents, Jay and Pa tricia Fidorra, and my siblings Kathy and Nick, for always loving me and being there for me no matter how far away I am. This work was supported by a grant from Biodiversity Research Institute and the U.S. Fish and Wildlife Service.
5 TABLE OF CONTENTS pa ge ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 7 LIST OF FIGURES ................................ ................................ ................................ .......... 8 ABSTRACT ................................ ................................ ................................ ..................... 9 CHAPTER 1 INTRODUCTION ................................ ................................ ................................ .... 11 2 SELECTION OF CONSTRUCTED AND NATURAL WETLANDS BY FORAGING GREAT EGRETS AT MULTIPLE GEOGRAPHIC SCALES ............... 16 Background ................................ ................................ ................................ ............. 16 Methods ................................ ................................ ................................ .................. 20 Study Area ................................ ................................ ................................ ........ 21 Agricultural Wetland Systems ................................ ................................ ........... 21 Satellite Telemetry Study ................................ ................................ .................. 22 Classification of used and available wetland habitat ................................ .. 23 Analysis of habitat selection ................................ ................................ ....... 25 Aerial Survey Study ................................ ................................ .......................... 26 Results ................................ ................................ ................................ .................... 27 Satellite Telemetry ................................ ................................ ............................ 27 Use of constructed wetlands ................................ ................................ ...... 28 Selection of constructed wetlands ................................ .............................. 29 Aerial Surveys ................................ ................................ ................................ .. 30 Discussion ................................ ................................ ................................ .............. 30 Ponds as Great Egret Foraging Habitat ................................ ............................ 31 Agricultural Wetlands as Great Egret Foraging Habitat ................................ .... 32 Summary ................................ ................................ ................................ .......... 35 3 LOCAL AND LONG DISTANCE MOVEMENT PATTERNS OF TWO GREAT EGRETS POPULATIONS ................................ ................................ ....................... 43 Ba ckground ................................ ................................ ................................ ............. 43 Methods ................................ ................................ ................................ .................. 46 Capture and Tagging ................................ ................................ ........................ 46 Home Ranges and Fl ight Distances ................................ ................................ 48 Statistical Analyses ................................ ................................ .......................... 49 Results ................................ ................................ ................................ .................... 49 Capture and Telemetry Data Summary ................................ ............................ 49 Local Movements ................................ ................................ ............................. 49
6 Long Distance Movements ................................ ................................ ............... 50 Movement Strategies ................................ ................................ ....................... 53 Discussion ................................ ................................ ................................ .............. 54 Local Movements ................................ ................................ ............................. 54 Long Distance Movements ................................ ................................ ............... 55 Variety in Movement Strategies ................................ ................................ ........ 58 Summary ................................ ................................ ................................ .......... 61 4 CONCLUSION ................................ ................................ ................................ ........ 69 LIST OF REFERENCES ................................ ................................ ............................... 72 BIOGRAPHICAL SKETCH ................................ ................................ ............................ 82
7 LIST OF TABLES Table p age 2 1 Proportions of habitat types available within the study area, home range, and 20 km radius circle and the proportion of satellite locations falling within each foraging habitat for great egrets in Louisiana, USA. ................................ ........... 37 2 2 Proportions of habitat types available within the study area, home range, and 20 km radius circle and the proportion of satellite locations falling within each foraging habitat for great egrets in South Carolina, USA. ................................ ... 38 2 3 Results of compositional analysis for the selection of foraging site habitat by great egrets in South Carolina. ................................ ................................ ........... 40 3 1 Distance and speeds for long distance flights (>300 km) of satellite tagged great egrets ................................ ................................ ................................ ........ 67 3 2 Movement strategies employed by great egrets followed over both the winter and breeding season and the proportion of the population utilizing each strategy. ................................ ................................ ................................ .............. 68
8 LIST OF FIGURES Figure page 2 1 Study area extent defined by 20 km radii around home range centers for great egrets tagged with satellite transmitters ................................ .................... 36 2 2 Average composition of habitat types used by great egrets tagged with satellite transmitters during daylight hours in Louisiana and Sout h Carolina ...... 39 2 3 Flight transects and land cover map of area surveyed for great egrets in Louisiana, USA. ................................ ................................ ................................ .. 41 2 4 Selection ratios for habitat types used by foraging great egrets observed during aerial surveys near breeding colonies. ................................ .................... 42 3 1 Average distance from nightly roost to subsequent foraging site for great egrets tagged with GPS transmitters in LA or SC. ................................ .............. 62 3 2 Comparison of 90% kernel ranges between seasons and capt ure location of great egrets tagged with GPS transmitters. ................................ ........................ 63 3 3 Southward long distance movements of 3 great egrets during the 2010 2011 winter ................................ ................................ ................................ .................. 64 3 4 Distances between winter season and breeding season ranges for 41 great egrets tagged during winter in LA (n=13) and SC (n=28) ................................ .. 65 3 5 Long distance northward movement s between winter and breeding season by three great egrets. ................................ ................................ ......................... 66
9 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of M aster of Science MOVEMENT PATTERNS AND THE RELATIVE IMPORTANCE OF CONS T R UCTED AND NATURAL WETLANDS TO GREAT EGRETS IN THE SOUTHEASTERN U.S. By Jason C. Fidorra August 2012 Chair: Peter Frederick Major: Wildlife Ecology and Conservation I studied t he m ovements and habitat selection of great egrets ( Ardea alba ) in the southeastern U.S. and compare d selection of human constructed wetlands to natural wetlands. Adult great egrets in Louisiana and South Carolina were tracked using satellite transmitters for up to one year. I analyzed habitat selection of home range s and selection of specific wetland type s used for foraging. I also compared use of agricultural and natural wetlands through aerial surveys at a Louisiana location where both wetland type s were abu ndant. I observed significant difference s between selection of constructed and natural wetland s as foraging site s i n SC where constructed ponds were selected over a ll other habitat types ( P <0.001). C rayfish aquaculture ponds were selected over natural wet lands in Louisiana especially when ponds were being drained R ice field s w ere selected over natural wetlands when the crop was short but had been flooded for at least a month Overall, a gricultural wetlands and constructed ponds provided attractive foragi ng opportunities for local populations but did not appear to influence broad s cale
10 movements of tagged birds. Depth, vegetation, and timing of inundation may limit use of these foraging sites. Within populations, different individuals used migratory, nomad ic, and sedentary movement strategies. Small patches of habitat could support individuals year round, while others conducted long distance movements travel ing up to 877 km/day at speeds reaching 79.9 km/h Travel was usually at night in a roughly straight line fashion, and often over large bodies of water far from sight of any landmarks, suggesting a target destination and true navigational abilities.
11 CHAPTER 1 I NTRODUCTION Habitat selection is a behavioral response resulting in a disproportional use of re sources in order to influence the survival and fitness of an individual (Jones 2001) Therefore, determining selection is important for understanding the biological requirements of an (Manly et al. 2002). Movement is one mechanism by which individuals can choose among available habitats and habitat selection and movement processes are intimately related; movement is p artly driven by habitat selection, whereas habitat selection is a process that is the consequence of movements (Martin 2009) Mobile species can remain within suitable habitat or if they have the ability, they can relocate as habitat conditions or their n eeds change High proportions of species that have evolved within the continuous vegetative cover of forest biomes are notoriously ill adapted for relocation as habitat destruction and conversion spreads ( Bierregaard et al. 1992 ; Sieving et al. 1996 ; Moore e t al. 2008 ). However, animal species of open habitats, such as large wetlands and grasslands are quite often highly adapted for long distance movements allowing them to search for optimal resource conditions ( Weller 1999 ; Dodman and Diagana 2007 ). Therefor e, while habitat selection is a key process determining the demography and success of any species, animals of open habitats with high mobility are likely to locate isolated habitat patches that have been fragmented as a result of human development and prov ide information regarding the relative suitability of these patches to others within the landscape. Wetland ecosystem s have been greatly modified by human activities over the past century ( Dahl 2006 ). While many wetland s have been destroyed or degraded, n e w
12 human constructed wetlands have also been created (see Chapter 2 ) These include ponds, reservoirs, impoundments, and flooded agricultural wetlands; and comprise a rising percentage of the wetland area in the U.S. With these widespread changes in the wet land landscape, there is a need to understand the ability of c onstructed wetlands to fill the ecological roles provided by natural wetlands particularly in regards to providing habitat for wetland obligate species Many wetland environments are naturally variable in both space and time, and wetland species have evolved a multitude of ways of surviving these dynamic conditions Some amphibians use drying as a cue to undergo metamorph osis into terrestrial forms (Denver 1997) lungfish can remain underground in aestiva tion for years (Fishman et al. 1992) and bird species conduct incredible movements between usable wetland patches in response to wetland conditions. Waterbirds are particularly adapted to make movements in responds to habitat: b ar tailed godwits ( Limosa lapponica ) fly non stop a cross the Pacific (Gill et al. 2005), bar headed geese ( Anser indicus ( Sterna paradisaea ) travel from pole to pole twice each year (Hatch 2002 ). These movements are thought to be primarily undertaken in response to changing foraging conditions (Pineau 2000 ; Dodman and Diagna 2007) T heir prey resources are patchily distributed and this increases the complexity of understanding successful foraging behavior. P rey availability for such mobile species is influ enced by global climate ocean currents, and variation in local factors including hydrology, rainfall, vegetation, and tempera ture (Kushlan and Hafner 2000). Wading birds ( Ciconiiformes: egrets, h erons, bitterns, storks spoonbills, and ibises) in particular, are sensitive to prey availability
13 (Kushlan and Hafner 2000 ; Crozier and Gawlik 2003 ; Frederick et al. 2009) which appears to be the primary driver of both breeding success (Frederick and Coll opy 198 9 ; Maddock and Baxter 1991 ; Hafner et al. 1993) and over winter survival ( Butler 1994 ; Cezilly 1997). Therefore, they are dependent upon their ability to locate and exploit patches of prey year round (Frederick and Spalding 1994) and the ir movement s trategies have evolved to cope with this chal lenge (Kushlan 1986; Frederick and Ogden 1997). However, many details regarding the annual movements remain unknown because we have lacked way s to study movements of many species across broad scales. G reat egret s ( Ardea alba ) are a widespread ciconi i form species common in both temperate and tropical wetlands. Their large distribution, abundance, size, and colonial behavior have made them relatively easy to study and much is already known about their microhabitat selection, foraging habits, and breeding ecology (Mc C rimmon et al. 201 1 ) They are a suitable species for studies of habitat selection and movement as t hey are wetland generalist able to exploit a variety of wetland types ( Chapman and Howard 1984 ; McCrimmo n et al. 2011) and individuals are known to conduct long distance movements ( Coffey 1943 ; Coffey 1948 ; Byrd 1978 ; Mikuska et al. 1998 ; Melvin et al. 1999). T hus they should provide insight into the relative attractiveness of many different wetland habitats a cross a broad area My research focuse d on the habitat selection and movements of great egrets using s atellite t racking of individuals from two wintering populations in the southeastern U.S. Satellite tracking p rovide d me with the ability to collect unbi ased location data on great egrets on a daily basis. In Chapter 2 I report on habitat selection and compare
14 relative use of constructed and natural wetlands by individuals at multiple scales using data from marked individuals. Since these animals were mar ked in relatively small areas that did not necessarily contain high proportions of constructed wetlands, or constructed wetlands of all types, I also examined habitat selection by a breeding population of great egrets in a landscape w here both natural and agricultural wetlands were abundant While use of various agricultural wetlands by wading birds has been d ocumented ( Martin 1985; Fasola and Ruiz 1996 ; Elphick 2000; Czech and Parsons 2002 ; Huner et al. 2002 ; Ma et al. 2004 ; Stafford et al. 2010 ) use alon e provides only limited information regarding the importance of these habitats. Information regarding the relative selection of these constructed wetlands compared to natural wetlands is needed in order to understand whether these wetlands are of similar q uality and supporting individuals within the population. D influenced by the availability of these wetlands will allow us to make predictions as human modification of wetland landscapes increases. Birds can uti lize a variety of movement strategies in response to changing environmental conditions. Some birds are sedentary, while others conduct nomadic or migratory movements. Identification of these different strategies inform us of the ecology of these species an d enable us to understand regional population trends, and each of these different movement patterns present different challenges for species management and conservation ( Boyd et al. 2008 ). Unfortunately, we have only limited information regarding the broad scale movement patterns used by most wading bird species. In Chapter 3 I de scribe the movement patterns employed by marked individuals over an annual time period I present detailed data regarding long distance
15 movements that were conducted during the st udy which provides new information regarding the speed and timing of flights by this species.
16 CHAPTER 2 SELECTION OF CONSTRU CTED AND NATURAL WET LANDS BY FORAGING GREAT EGRETS AT MULT IPLE GEOGRAPHIC SCAL ES Background While wetland loss remains a conservat ion concern, the rate of loss in the U.S. has slowed in recent decades and the latest censuses show marginal increase s in wetland area due in part to the construct ion and management of wetlands by humans (Dahl 2006, 2011). Constructed wetlands are aquatic features in which the depth and inundation period are controlled by human design. These include ponds, reservoirs impoundments, and flooded agricultural wetlands ; and comprise a rising percentage of the wetland area in the U.S. For example, n early 282,000 ha (12.6% increase) of freshwater ponds were created in the contiguous USA between 1998 and 2004 (Dahl 2006). With these widespread changes in the wetland landscape there is a need to understand the ability of human constructed wetlands to fill the ecolo gical roles provided by natural wetlands. Here, I explore the importance of constructed wetlands to wa ding birds Wading birds (egrets, herons, bitterns, storks spoonbills, and ibises) forage and breed in wetland s and are a predatory group feeding on a va riety of aquatic invertebrates, fish, and amphibians, with larger species opportunistically taking reptiles, birds, and small mammals. They are sensitive to prey availability ( Kushlan and Hafner 2000 ; Crozier and Gawlik 2003 ; Frederick et al. 2009) which appears to be the primary driver of their breeding success (Frederick and Collopy 198 9 ; Maddock and Baxter 199 1; Hafner et al. 1993 ) and over winter survival ( Butler 1994 ; Cezilly 1997 ). Prey a vailability is dependent upon both the density and accessibilit y o f prey which are influence d by various factors. Hydroperiod (duration of surface water) influences species composition (Kushlan and
17 Hafner 2000 ; Lawler 2001 ), prey density, and the type of predators present (Batzer and Wissinger 1996) in wetland commun ities. Following inundation, species richness and density of the invertebrate community generally i ncrease up to 6 months before level ing off (Batzer and Wissinger 1996), and perennially flooded wetlands are more likely to support fish populations (DeAngel is et al 1997 ) Vegetation provides fo od and refuge for many prey species (Crowder and Cooper 1982), but emergent and submergent vegetation can obstruct access to wading birds (Pierce and Gawlik 2010 ; Lantz et al. 2010, 2011 ). Increasing water depth also r educe s access to habitat by wading birds which are limited by leg length (Powell 1987). Season, water temperature, oxygen, trophic status, and substrate are additional factors which can influence prey availability for wading birds. Also the establishment and maintenance of some prey populations depends upon landscape variables such as the distance between wetlands and the permeability of the matrix between them (Joly et al. 200 1 ). Constructed wetlands are a broad mix of these features, and wading bird s may not be attracted to all constructed wetland types. In general, however, it is unclear how constructed wetlands function by comparison to mosaics of natural wetlands. W ading bird s are known to use fields flooded for rice ( Oryza sativa ) production ( Fasola and Ruiz 1996 ; Elphick 2000 ; Czech and Parsons 2002 ; Stafford et al. 2010 ), various aquaculture sites ( Glahn et al. 2002 ; Huner et al. 200 2; Ma et al. 2004; Cheek 2009 ) and constructed ponds ( Edelson and C o llopy 1990 ; White 2003 ) However, most of these s tudies did not compare use to availability (Johnson 1980 ; Manly et al. 2002), or ca me from situations in which non constructed wetlands were not readily available.
18 M ost wading birds do not nest in rice fields but forag e in them during the breeding season (Pierlu i ssi 2010) when energetic needs are 2 3 times those in the non breeding season (Kushlan and Hafner 2000). I n regions w here natural wetlands have been lost, populations of wading birds are dependent upon rice fields for foraging ( Fasola et al. 199 6 ; Fasola and Ruiz 1 996) b ut w hether rice fields provide foraging habitat comparable t o natural wetlands is un clear. W ading birds often prefer natural wetlands over nearby foraging sites (T ourenq et al 2001 ; Sundar 2006; Bellio et al. 2009 ) Ho wever cal oric intake by wading bird s foraging in rice fields may be insufficient (Sizemore 2009) in which case they may be serving as ecological traps (Dwernychuk and Boag 1971) Thus the question remains whether rice fields are functional ly equivalent to natural wetlands as adequate foraging sites At aquaculture sites, the high density of stock and other aquatic prey colonizing them may provide excellent foraging opportunities for wading birds. Rapidly increasing populations of several wading bird species in Loui siana corresponded with the expansion of cray fish aquaculture (Fleury and Sherry 1995 ) suggesting aquaculture may support larger populations However, all aquaculture sites do not appear to be equal Access to aquaculture ponds can be restricted to wading birds by pond depth (Powell 1987 ; Cheek 2009 ) or management practices employed to deter birds from using aquaculture sites. While Ma (2004) found similar abundance s of wading birds in fish and crab aquaculture ponds as on natura l tidelands, Cheek (2009) found that caloric intake by wading birds at shrimp farms in Ecuador was less than for birds foraging on natural mudflats The inconsistencies regarding the benefits of rice fields and aquaculture ponds for wading birds suggest th at further research is required
19 to determine when, where, and under what management practices bird populations benefit from agricultural wetlands. Wading bird habitat selection is dependent upon the scale at which it is measured (Stolen et al. 2007). As se lection is a hierarchical process, multiple scales are required to understand how species choose habitats (Johnson 1980 ; Aebischer 1993). Wading birds can select habitat over a broad area and individuals and populations are capable of responding to prey av ailability at regional scales (Frederick et al. 1996 ; Frederick and Ogden 1997). An a priori delineation of available habitat and study area boundaries can affect the results of selection analyses without a biological basis (Porter and Church 1987). G reat egrets ( Ardea alba ) are a cosmopolitan long legged ciconi i form bird common throughout many temperate and tropical regions globally As w ide ranging wetland generalist s, great egrets are able to exploit a variety of wetland types ( Chapman and Howard 1984 ; McCrimmon et al. 2011) and they display plasticity in foraging tactics and prey consumption ( Dimalexis and Provetsi 1997 ; Gawlick 2002). I selected this species, in part, because its behavioral flexibility and success in complex landscapes provided the opp ortunity to assess the relative attractiveness of different potential foraging habitats at local, landscape, and regional scales (see Chapter 3 ) In this study, my objective was to quantify selection of foraging habitats by great egrets and specifically to compare the attractiveness of constructed wetlands to natural wetlands Constructed wetlands have the potential to maintain water levels despite seasonal conditions and thus may provide an alternate source of food when natural we tlands are dry or too deep ( Sundar 2004) and a stable hydroperiod may increase
20 densities of preferred prey (e.g. fish). Wading birds respond positively to the concentration of prey during drying of natural wetlands (Kushlan 1976). If management practices allow water levels in vario us constructed wetlands within a landscape to fluctuate asynchronously, they could create a patchwork of ephemeral, high quality foraging sites throughout the year. I hypothesized that constructed wetlands would provide attractive foraging opportunities fo r great egrets and would be selected over natural wetlands. I predicted that great egrets would show a significantly more positive selection of constructed wetlands than natural wetlands at the scale of home range selection and foraging site selection if t his hypothesis was correct. I used free ranging satellite tagged egrets in two wetland dominated regions of the southeastern U.S. to test my hypothesis at scales defined by the movement patterns observed by individuals during b oth the winter and breeding s eason. I also determined selection with in the breeding season across a landscape with a pproximately equal availability of both natural and agricultural wetlands. Methods I compared selection of constructed wetlands to natural wetlands by great egrets in t wo use availability studies U se information was collected both from satellite tagged great egrets and from untagged breeding egrets surveyed systematically in a wetland landscape containing both agricultural and natural wetlands. Satellite telemetry allo wed me to follow individuals in an unbounded geographic area and examine habitat selection based on movements of individuals. Survey of breeding individuals within an area of rice/crayfish culture allowed me to examine the relative importance of an agricul tural system thought to be highly beneficial to birds.
21 Study A rea I studied birds in the coastal regions of Louisiana (LA) and South Carolina (SC) (Figure 2 1) These areas are important to wintering (Mikuska et al. 1998) and breeding populations of wadin g birds Both regions have a humid subtropical climate and are centered on major river deltas and estuaries within the coastal plains Both regions contain a large proportion of wetland area ranging from 73.3% (LA ; Table 2 1) to 39.4% (SC ; Table 2 2) and p ossess a concentrate d area of impounded wetlands related to past or present agricultural practices The LA study area included the major metropolitan areas of New Orleans and a portion of Baton Rouge, while SC included Charleston and Myrtle Beach, providin g each with a similar portion of urbanized land cover (8 9%). Agricultural W etland S ystems Rice and crayfish production is often combined in a rotational manner in southern Louisiana. Rice fields typically are flooded in spring as rice is planted (March M ay) and a pproximately 10cm of water is maintained in the field for weed control until draining and harvest (Aug S ep) A fter the harvest, fields may be planted with soybeans or another terrestrial crop, or flooded to attract waterfowl over the winter and/or for cray fish production. Cray fish production involves shallow flooding (30 40cm) i n the fall (Sep Oct) often following the rice crop, and drainage after the harvest the following May Jun (McClain et al. 2007) A rotation al system of rice cray fish fallow or rice cray fish soybean over a two year period is the most common method ; a ccount ing for ~70% of cray fish farming in Louisiana (McClain pers. comm. Jun 2011 ). T iming is often staggered so that there will
22 be cray fish fields available in one year to restock rice fields that will produce cray fish the next. In South Carolina, many defunct rice fields from the 18 r emain along the tidal river floodplains Many of t hese are now on w ildlife r efuges and game lands managed f or a combination of wa t erbirds throug hout the year. Water levels may be lowered in the spring and summer for migrant shorebirds and breeding wading birds, and raised in the fall to grow aquatic vegetation for waterfowl that use the flooded impoundments during the winter Private landowners ty pically flood their impoundments for waterfowl in the winter and drain for planting corn or millet in the early spring. The timing and management of individual fields varies by manager, location, intent, and season and thus a landscape of deep and shallowl y flooded, planted, and barren fields exist through out the year. Satellite Telemetry Study I used satellite telemetry to study movements and habitat selection of individually marked adult Great egrets. From September 2010 through February 2011, g reat egret s were captured in coastal LA and SC at foraging and loafing locations using a pneumatic net gun fired from a moving automobile ( Meyer et al. in prep ) So lar powered GPS satellite transmitter s ( Model 22GPS, Northstar Science and Technology ) were placed on adult great egrets using a Teflon ribbon backpack style harness Total mass of the attachment (35 g) was kept to less than 4 The GPS transmitters were programed to collect 2 locations per 24 hrs : 1 between 0800 and 0900 h r s local standard time when birds were presumed to be foraging ( Wiese 1975; Kushlan 1978 ) and a second from 0200 to 0300 hrs when I presumed birds to be at roost sites I used 1 foraging location per day to ensure independence
23 within locations ( Gawlik 2002 ). Data collecte d from capture through August 15, 2011 was included in the analysis (maximum period of data collection of 1 1.5 months for any individual ) Classification of used and available wetland habitat I adopted the Cowardin et al. (1979) definition of a wetland used in the National Wetland Inventory (NWI ; USFWS 2011 ). Deepwater habitats such as lakes, rivers, and marine environments are not wetlands, but are still important aquatic features for wading birds included in this study and the NWI I extended the definitio n to include the agricultural impoundments described more fully below. reference to any wetland features that are not impounded, diked, or excavated; but acknowledge that wetlands identified as natural within the study may be im pacted by human activity. I used a geographic information system ( Arc GIS v. 9.3; ESRI Redlands, California) and the A BODE extension (Laver 2005) to calculate 90% fixed kernel home ranges f or individual s for which >30 daytime locations were collected (Seam an et al.1999) using a bandwidth determined by least squares cross validation ( Worton 1989 ) I considered habitat as available to each individual if it was within a 20 km buffer around t he center of each 90% kernel contour polygon Twenty kilometer s is a di stance used previously to define habitat available to great egrets (Custer et al. 2004 ; Leberg et al. 2007 ) and was appropriate for this study as it approximate ly matched the maximum distance (22 km) traveled between roost and subsequent foraging site by a ny tagged egret and included all habitat within the kernel home ranges If 2 or more disjoined polygons were created for an individual buffers were created from each center poi nt
24 The buffers for all individuals within each of the 2 st ates (SC and LA) wer e merged to delineate my study area s I identified wetlands within the study area using the NWI I reduced the NWI categories to 5 classes: emergent wetland, forest/scrub wetland, pond/lacustrine, riverine /canal and unconsolidated shore. Each of these cat egories w as further divided into one of the following categories: Constructed, Natural, and Riverine habitat. Wetlands categorized as impounded, diked, or excavated in the NWI were grouped as constructed wetlands ed Riverine wetlands (including canals in LA) presented too many subtleties of modification to be classified cleanly as constructed or natural, and Land cover not classified in a wetland category was lumped into a t errestrial habitat type. igital scans with 1 m pixel resolution of 1:40000 scale aerial photographs taken in 2010 and 2011for the National Agricultural Imagery Program ( USDA 201 0 201 1 ) I di gitized any unclassified ponds > 1000m 2 and canals >10m wide I also removed wetlands that had become occupied by urban and agricultural development. I assigned n ewly identified ponds to the sub class of constructed wetlands and canals to r iverine habitat type I identified w etlands surrounded by dikes or levees as constructed and confirmed or updated their status in the NWI layer. I identified t hese features by cont rasting water depth or vegetation compared to t heir surroundings visible levees and/ or stru ctures in place that could allow for depth manipulation Since great egrets can only utilize the shallow boundaries of deep water environments, I placed a 5 m buffer inside NWI wetlands originally clas sified as sub
25 tidal estuarine /marine, riverine, pond, and lacustrine to better approximate the area available to egrets. This also effectively excluded open ocean from the study areas. A reas for each habitat were calculated using the USA conti guous Albers E qual A rea C onic coordinate system Only daytime point s with estimated accuracy error 100m and reported velocity 4 m/s were retained for analysis of foraging habitat use by the great egrets In addition, daytime locations at known breeding sites were excluded. Points were assigned to the habitat class of the NWI wetland that they were located within, or the closest habitat within their reported margin of error Points not within this proximity of wetland s were classified as terrestrial. Analysis of h abitat selection I compare d composition of home range s to th e proportion s of habitat available within the study area For each individual, I also compared the proportion of egret locations in each wetland type to the compos i tion of the 20 km buffer a round the home range center I first tested for a difference betwee n the selection of the broad categories of constructed and natural wetland s. I f significant differences existed, I tested selection of specific wetland types to understand the pattern. To determine the effect of my classification of riverine/canal habitats I reanalyzed the data including them with constructed habitats. I used c ompositiona l analysis to rank habitats and compare selection between habitat types (Aebischer et al. 1993) Data were analyzed in Program R using the adehabitatHS package (Calenge 20 06) using Wilkes Lambda to test for overall selection and a randomization test with 1000 replicates to compare selection between habitat types ( alpha = 0.05 )
26 Aerial Survey Study I conducted aerial surveys of wading bird habitat use over a landscape of mi xed agricultural wetlands and natural wetlands located outside of the geographic limits of the satellite telemetry study. This area included the southern portion of the cray fish and rice agricultural area in south central LA and an expansive area of natura l emergent wetlands to the south (Figure 2 3 ). On the boundary between the se 2 primary land cover types were several great egret colonies, a situation I viewed as ideal for testing the prediction that great egrets prefer foraging in these highly productive agricultural wetlands I identified 4 colonies from 2008 that c ontain ed >100 great egrets (LNHP 2008) and that were located along the boundary of the agricultural region and southern marshes I placed 30 km buffers around these colonies to delineate the s tudy area boundary. This was typically the maximum distance that foraging great egrets travel from their colony locations to foraging sites ( Custer and Osborn 1978 ; Sm ith 1995 ; Custer and Gali 2002 ) S urvey flight transects were positioned at random distan ces north and south of the geographic center of the study area and oriented in an east west direction The length of e ach transect was also randomly determined but were constrained by the boundary of the study site I counted birds on these transects f rom a Cessna 172 during the 2010 g reat e gret breeding season on 27 March, 21 May, and 25 June. These time periods correspond ed to periods of high food demands by nesting birds. Flights were conducted between 0800 1200 hrs with the same 2 observers and pilot co nducting all 3 surveys from an altitude of 500 feet and a ground speed of 120 145 km / h. Windows and wing struts were marked to delineate a 250m wide strip of ground as viewed out both sides of the plane
27 parallel to flight direction (Norton Griffiths 1978) Within these strips, all foraging egrets and habitat type s w ere recorded H abitat categories were rice paddy, cray fish pond, emergent and other The other category included all terrestrial land cover and forested wetlands An egret was considered forag ing if it was standing in an aquatic habitat or along the adjacent shore. Birds in flight, perched in trees or nesting at colonies were not counted. Photographs were taken of aggregations >10 individuals to confirm number and species. The NWI and NA IP ima gery were used to separate constructed emergent wetlands from natural wetlands Selection ratios (Manly et al. 2002) comparing habitat used by great egrets to habitat available within the survey strips were created in Program R using the adehabitatHS packa ge (Calenge 2006) and compared using Bonferroni confidence intervals. Independent double observer counts (Nichols et al. 2000) were conducted within the study area during travel between transects but not during survey counts. Sightings were categorized by habitat type and size of foraging aggregation. Groups of 3 or more birds were analyzed se parately from foraging pairs and individuals to account for potential differences in the detections of groups and individuals Detection probabilities were estimated b y habitat type, observer, and group size in the software program DOBSERVE and compared using AICc (Hines 2000). Results Satellite T elemetry During the fall and winter of 2010 2011, 41 GPS equipped satellite transmitters were placed on great egrets and >30 daytime location points were gathered for 30 individuals (LA =1 1 SC = 19). The average number of foraging location points collected for each bird was 117.8 12.7 SE Eighty three percent of the points retained for
28 analysis had reported accuracy error < 26m and 9 6 % were collected between 07 00 and 1 1 00 hrs when wading birds are often foraging ( Wiese 1975; Kushlan 1978) The study areas defined by a 20 km radius around all home range centers in L A and S C (Fig 2 1) were 9,932 km 2 and 8,484 km 2 (excluding open ocean), respectively. Study area composition (Table 2 1 and 2 2) differed most between the 2 states in the proportion of terrestrial land cover and emergent wetland area The total proportion of wetland area available to individuals was greater in LA than in SC Constructed wetlands made up a similar percent of total wetland area within the LA (4.31%) and SC (4.47%) st udy area s. Emergent wetlands were the most commonly used habitat in both study areas, followed closely by riverine/canal habitat in L A and construc ted ponds in SC (Figure 2 2). Use of c onstructed w etlands All but two of the tagged egrets from Louisiana were recorded in constructed wetlands at least once Louisiana egrets occupied constructed wetlands at 10.8% 5.2 SE of point locations Constructed e mergent w etlands were used by 6 of 11 egret s in Louisiana, and only 1 egret used construct ed forest/scrub wetlands C onstructed ponds were used by 6 of the 11 egrets but one of these individual s was recorded 146 times (56% of its locations ) in constructed ponds within the New Orleans metropolitan area Egrets in South Carolina used constructed habitats at 41.7 % 8.0 SE of point locations Four of the 19 egrets in SC used constructed wetlands >80% of the time, mostly occupying constructed ponds/lake s. Const ructed emergent wetlands were used by 3 of the 19 SC egrets, and 1 bird made use of constructed forest/scrub wetlands.
29 The rare habitat classification of constructed unconsolidated shore was never occupied in either state. None of the satellite tagged egre ts in either state appeared to use functioning agricultural wetlands. However, these wetlands were mostly absent from the study areas. The historic but dysfunctional rice impoundments along the river floodplains in Georgetown County, SC were used 11 times by a single tagged egret over a 38 day period Selection of c onstructed w etlands In LA I failed to detect overall selection at the home range scale (Wilkes Lambda = 0.6236, P= 0.252), or foraging site scale (Wilkes Lambda = 0.6288, P= 0.271) and constructed wetlands were not selected over natural wetlands at either scale ( P= 0. 943 P= 0.575 respectively). The trial including r iverine habitat within the constructed category produced similar results (Wilkes Lambda = 0.6384, P= 0.156), with constructed wetlands n ot selected over natural wetlands ( P= 0.098). In SC, habitat selection at the home range scale was detected ( Wilkes Lambda = 0. 3475 P= 0. 00 2 ) Constructed wetlands were selected over r iverine habitat (p <0.001 ), but not over natural ( P= 0. 317 ) o r terrestrial ( P= 0.891 ) habitat at the home range scale. Overall selection of foraging sites within 20 km of each home range center was also detected (Wilkes Lambda = 0.0559, P= 0.001) and c onstructed wetlands were selected over natural wetlands, riverine, and terrestria l habitats (p<0.001 ). Further investigation of foraging site selection in SC by comparisons of specific wetland types determined that constructed pond/lake habitat was selected more strongly than all other habitat types (Table 2 3 ; p < 0.001). T here was a si gnificant difference in the selection of each of the 3 constructed habitat types where constructed ponds were selected greater than
30 constructed emergent ( p<0.001), which was selected over constructed forest/shrub wetlands ( P= 0.008) A erial Surveys The area within 30 km of great egret colonies in LA covered 4,974 km 2 (Figure 2 3 ). I surveyed approximately 137.5 km 2 of th is area (2.76%) within the survey transect strips and record ed a total of 1333 foraging great egrets Analysis of great egret detection rates i ndicated that the null model incorporating no effect of observer or habitat was the best model for both group sizes. Competing ~ However, t he differences in detection est imates between these models and the null were considered non biologically significant as estimates were all within 3 9% of each other. Therefore, no adjustments to the count data were made for observer or habitat effects I mpoundments used for cray fish pro duction were the only habitat type consistently selected more than natural emergent wetlands (Figure 2 4 ), and used more than e x pected given the ir availability in every survey The s election of rice fields by great egrets changed over time : flooded rice fi elds were scarcely used in March selected positively in May and used in proportion to their availability in June. I did not detect a significant difference between the selection of natural emergent and constructed emergent wetlands in any month Discussi on Overall, I did not find evidence that great egrets favor constructed habitats over natural wetlands. Rather, the pattern of selection changed between study areas and by wetland type Foraging site selection differed for e ach constru cted wetland type in SC
31 (Table 2 3) C onstructed ponds were highly selected a s foraging sites t here but this pattern was not detected in LA where I did not detect differences between the selection of constructed and natural wetlands ed habitat (Figure 2 2), but this category included aquatic features along a gradient of human control. Many birds foraged frequently along wide, navigable canals that categories. I ran the analyses comparing s election of constructed and natural wetlands again, this time including the riverine habitat class in the constructed category and observed the same results. T he low use of most constructed wetlands during the telemetry study (Figure 2 2) combined with th e fact that these wetlands were generally uncommon (accounting for <5% of available wetland area in both study areas) suggests that most constructed wetlands are currently not very important to great egrets on a national scale. However, two constructed wet land types may be important for local populations: ponds and agricultural wetlands. Ponds as Great Egret Foraging Habitat Constructed ponds wer e abundant in the urbanized regions of both states E grets tagged in South Carolina selected constructed ponds mo re than any other habitat type while i n Louisiana, only the egret tagged within the New Orleans Metropolitan area utilized ponds extensively Since great egrets were captured with net guns fired from a slow moving vehicle, the majority of captures occurre d at roadside canals and constructed ponds. Individuals captured may therefore have been more predisposed to forage in these habitats than a true random sample of the population. The fact that so many egrets used constructed ponds so frequently and through out the duration of the
32 study indicates that constructed ponds provide important foraging opportunities for great egrets, particularly in urban environments. However, conclusions regarding the importance of these habitats for a typical great egret should b e made with caution. M any constructed ponds are deeper (1 15m on golf courses, White 2003) than the maxi mum depth accessible by great egrets ( 28cm, Powell 1987) which limits their foraging to pond edges. E dges may be ideal foraging locations for wading bi rds as prey fish seek shelter from aquatic deepwater predators in shallow water ( Werner et al. 1983 ; Power et al. 198 5 ) despite predation risk by wading birds (C rowder et al. 1997). O ther studies have also found great egrets to be attracted to constructed ponds at golf courses ( White 2003 ) and phosphate mines (Edelson and Collopy 1990) Constructed ponds may allow great egrets to coexist with urban development, although important to note that no birds were found exclusively in ponds. This suggest s that compatibility with development is only likely where there are other habitats for roosting and feeding. Agricultural Wetlands as Great Egret Foraging Habitat This was the first study to quantify habitat selection by wading birds in a cray fish aquaculture s ystem. In cray fish aquaculture, farmers mimic natural ecosystems by providing a community of plants and invertebrates for cray fish to eat. This community, in addition to the stocked cray fish, provides prey for larger predators which attract great egrets F leury (1996) found that crayfish ponds can rival natural wetlands in term s of the number of fish present and that g reat egrets had higher foraging success and took more preferred prey items i n cray fish ponds. Strong s election of cray fish ponds in June was attributed to the draining of ponds. This reduction of water level provides an increasingly shallow environment of concentrate d pre y Du ring these drawdowns, cra y fish ponds ha ve significantly higher cray fish, fish, and total prey densities than natural wet lands
33 (Fl eu ry 1996) This pulse of food availability coincide s with the late nesting period for great egrets a time when nestling death from starvation is usually high, and likely has abundant food likely has a significant impact on local reproductive suc cess. The selection of rice fields changed over the study period, which I attribute to a tradeoff between increasing prey density and decreasing accessibility I n rice fields, wading bird prey r each es maximum abundance during the late summer prior to harve st ( Gonzalez Soliz et al. 1996; Lane and Fujioka 1998; Sizemore 2009 ) R ice fields may offer little prey for great egrets soon after inundation a prediction supported by nominal use of this habitat during March. I nvertebrate densit ies in Louisiana rice fie lds during May (Hohman et al. 1996) are comparable to those of natural emergent wetlands in the state ( Manley et al. 1992) and great egrets selected rice fields over natural wetlands in May. While some f armers in the region do stock to stock rice fields in late May and June with cra y fish for harvest the following spring in rotational practices, they typically wait until rice stalks are large enough to avoid damage from foraging cra y fish provide shade for temperature regulation, and deter predatory birds (M cClain pers. comm. June 2012), therefore, I do not believe th at the stocking of cra y fish was a major factor in attraction of egrets to these rice fields Despite the presumed higher prey densities i n June, selection of rice fields decreased from the May su rvey probably because of the coverage and density of rice stalk s that inhibits access ( Lane and Fujioka 1998; Fujioka et al. 2001 ; Sizemore 2009 ) Rice fields in southern LA do not appear to be as important as rice fields in other parts of the world for gr eat egrets. At my study site, rice fields only provide suitable foraging habitat for a short part of the year (~2 months). Crayfish ponds and emergent
34 wetlands appear to be more important in supporting local great egret populations year round. However, as rice farming is usually an integral part of the crayfish production system, it is not possible to manage these habitats independently from a wildlife perspective. I originally anticipated that egrets tagged in Louisiana would at some point make use of this region of dense agricultural wetlands 200 km to the west of their capture locations. This was not the case and agricultural wetlands were generally absent from the habitat considered available to the tagged birds. While the farthest foraging foray recorded during the study was 22 km, several individuals moved distances many times further than 200 km (Chapter 3 ). Similarly, the area of historic rice impoundments was geographically in the center of the SC study area and within 200 km of any of the tagged birds i n that state, yet only 1 of the 19 egrets utilized these constructed wetlands My observations therefore provide no evidence of attractiveness at a statewide scale by these constructed wetlands I conclude that even when these constructed wetlands are at t heir most seasonally attractive, they are not magnets for egrets at a regional scale and are not responsible for supporting entire regional populations. It is often assumed that a species will select resources that are best able to satisfy its life requir ements, and that high quality resources will be selected over poor quality ones (Manly et al. 2002). However, there are situations in which selection may not reflect the quality of a habitat (Van Horne 1983). The relationship between habitat selection and fitness or reproductive success of great egrets was beyond the scope of this study and I have no evidence that these selected habitats function as ecological
35 traps. Exposure to structural hazards, disease, and toxins may be elevated in ponds and agricultur al areas where pesticides, herbicides, and run off are of concern and can affect wading bird health (Parsons et al. 2010). My findings highlight the importance of future research into the relationship between both agricultural wetlands and constructed ponds to wading bird mortality and reproductive success. Summary I observed strong selection at local scales for constructed pon ds and agricultural wetlands by great egrets in comparison with natural wetlands Selection of constructed ponds in SC coupled with consistent use indicated that the populations in this urbanized area might be supported to some significant extent by these features. In agricultural regions of LA, t he pulse of food during the draining of crayfish ponds coinciding with the nestling period i s likely important to the breeding success of local colonies Rice fields, however, were positively selected during only a short portion of the breeding season. At broader spatial and time scales there was no indication that regional populations were rel iant upon these agricultural wetlands.
36 Figure 2 1. Study area extent defined by 20 km radii around home range centers for great egrets tagged with satellite transmitters. The rice and crayfish impoundments in Louisiana (A) and abandoned rice plantati ons in South Carolina (B) are identified. A B
37 Table 2 1. Proportions of habitat types available within the study area, home range, and 20 km radius circle used to define available habitat for individuals, and the proportion of satellite locations falling withi n each foraging habitat for great egrets in Louisiana, USA. Habitat Type Scale Study Area Home Range 20 km Radius Point Locations Percent Percent SE Percent SE Percent SE Terrestrial 26.69 38.15 7.34 21.82 5.01 12.98 4.90 Emergent 40.58 35.61 8.28 5 9.82 6.96 31.84 8.77 Woody 29.05 22.72 5.62 13.65 4.07 11.78 3.26 Pond/Lake 0.14 0.05 0.02 0.11 0.03 0.50 0.33 Unconsol idated Shore 0.07 0.06 0.04 0.11 0.04 0.00 0.00 Constructed Emergent 1.47 1.01 0.52 2.18 0.34 3.28 2.35 Constructed Forest/Scr ub 1.58 1.42 0.89 1.94 0.77 2.41 1.62 Constructed Pond/Lake 0.11 0.22 0.09 0.09 0.04 6.69 5.43 Constrcuted Unconsol.Shore 0.01 0.00 0.00 0.01 0.01 0.00 0.00 Riverine /Canal 0.30 0.77 0.28 0.28 0.05 30.51 9.92
38 Table 2 2. Proportions of habitat types available within the study area, home range, and 20 km radius circle used to define available habitat for individuals, and the proportion of satellite locations falling within each foraging habitat for great egrets in South Carolina, USA. Habitat Type Scal e Study Area Home Range 20 km Radius Point Locations Percent Percent SE Percent SE Percent SE Terrestrial 60.64 65.31 3.79 59.91 1.18 4.94 2.18 Emergent 10.34 18.44 3.54 16.13 2.89 40.37 8.22 Forest/Scrub 25.87 10.69 3.58 20.16 2.64 6.31 2.52 Pon d/Lake 0.02 0.01 0.01 0.01 0.00 0.26 0.18 Unconsol idated Shore 1.23 3.43 0.92 2.45 0.45 3.80 1.76 Constructed Emergent 1.28 0.88 0.61 0.55 0.23 3.81 1.51 Constructed Forest/Scrub 0.22 0.09 0.04 0.16 0.02 0.19 0.14 Constructed Pond/Lake 0.26 1.09 0.15 0.32 0.03 39.90 8.15 Constru c ted Unconsol.Shore 0.00 0.01 0.01 0.01 0.00 0.00 0.00 Riverine 0.13 0.06 0.03 0.30 0.08 0.41 0.41
39 Figure 2 2. Average composition of habitat types used by great egrets tagged with satellite transmitters during da ylight hours in Louisiana and South Carolina. Error bars indicate SE.
40 Table 2 3. Results of compositional analysis for the selection of foraging site habitat by great egrets in South Carolina. Rank indicates the relative selection of habitats, with smal ler ranks being more highly selected. The sign indicates how selection of the row habitat differed from selection of column habitat type. Periods indicate no significant difference in selection. Habitat Type Significance of pairwise comparison of selecti on Rank PL*C EM EM*C PL FS US FS*C RI TER Constructed Pond /Lake (PL*C) 1 + + + + + + + + Emergent (EM) 2 + + + + + + Constructed Emergent (EM*C) 3 . + + + Pond / Lake (PL) 4 . + + + Forest / Scrub (FS) 5 . Unconsol idated Shore (US) 6 . Constructed Forest /Scrub ( FS*C) 7 . Riverine (RI) 8 . Terrestrial (TER ) 9 .
41 Figure 2 3. Flight transects and land cover map of area surveyed for grea t egrets in Louisiana, USA.
42 Figure 2 4. Selection ratios (+/ 95% CI) for habitat type s used by foraging great egrets observed during aerial survey s near breeding colonies A ratio >1 indicates habitats were selected more than expected given their avail ability. Note that
43 CHAPTER 3 L OCAL AND LONG DISTANCE MOVEMENT PA TTERNS OF TWO GREAT EGRETS POPULATIONS Background Understanding movement patterns at various scales is essential for understanding of the ecology, life history, behavior, and conservation of most animals (Rubenstein and Hobson 2004). Few taxa possess the capacity for undertaking broad scale movements as far and rapid as birds and no group of birds demonstrate this capa bility better than waterbirds : b ar tailed godwits ( Limosa lapponica ) fly non stop a cross the Pacific (Gill et al. 2005) bar headed geese ( Anser indicus ( Scott et al. 2009 ) and ar c tic terns ( Sterna paradisaea ) trav el from pole to pole twice each year ( Hatch 2002 ) Waterbirds evolved the ability to make su ch movements because the aquatic habitats they depend upon are highly dynamic Particularly, food resources are patchily distributed in space and time, being i nflue nced by global climate patterns ocean currents, and local factors including hydrology, rainfall, and temperature ( Kushlan and Hafner 2000 ) Thus, waterbird movements are primarily undertaken in response to foraging conditions (Pineau 2000 ; Dodman and Diag na 2007 ) T here are three general movement strategies used by birds for meeting their needs Birds may be 1) migratory: conducting regular back and forth movements betwe en two or more seasonal ranges 2) nomadic: conducting irregular and unpredictable move ments often in response to resources that are spatially and temporally unpredictable, or 3) sedentary : neither of the above ( White and Garrott 1990 ; Dodman and Diagana 2007 ; Boyd et al. 2008 ) While th ese definitions are mutually exclusive most specie s u se of them is not and subpopulations of the same species
44 may utilize different strategies (Boyd et al. 2008). In addition, dispersal is the movement of an individual away from the place of birth or population centers (Koford et at. 1994) and can describe c ertain movements of individuals that utilize any of the above strategies. Wading birds (hereafter used in reference to the long legged waders including herons egret bitterns, storks, spoonbills, and ibises) are a group of waterbirds dependent upon shallo w wetland s for foraging F ew other habitat type s are as spatially and temporally dynamic resulting in ephemeral food patches which are widely distributed (Hoffman et al. 1994) Wading birds are sensitive to prey availability ( Kushlan and Hafner 2000 ; Croz ier and Gawlik 2003 ; Frederick et al. 2009) which appears to be the primary driver of their breeding success (Frederick and Collopy 1988; Maddock and Baxter 1991 ; Hafner et al. 1993 ) and over winter survival ( Butler 1994; Cezilly 1997 ) Therefore, they ar e dependent upon their ability to locate and exploit patches of prey year round (Frederick and Spalding 1994), and their movement strategies have evolved to cope with this challenge ( Kushlan 1986; Frederick and Ogden 199 7 ) However, many d etails regarding the annual movements remain unknown because we have lacked a way to study movements across broad scales. The g reat egret ( Ardea alba ) is a widespread species, common throughout many temperate and tropical regions of the world They are w ide ranging wetland generalist s able to exploit a variety of wetland types ( Chapman and Howard 1984 ; McCrimmon et al. 2011 ) Great egrets breed along both Pacific and Atlantic coasts from Washington and Maine south to Argentina and Chile, and also utiliz e scattered interior locations in the U.S., particularly within the Mississippi River B asin ( Mc C rimmon et al. 2011). The
45 local movements of great egrets have been well studied during the breeding season. Studies of unmarked breeding individuals followed by plane have been usef ul in answering questions regarding local foraging flight distances, flight speed s and habitat selection (Custer and Gali 1978, 2002 ; Thompson 1978; Smith 1995; Custer et al. 2004) Band recovery studies have provided much of the current information regar ding larger scale movement s in North America (Coffey 1943; Coffey 1948 ; Byrd 1978 ; Mikuska et al. 1998 ; Melvin et al. 1999). Great egrets are considered migratory through much of North America, but some populations may be resident or disperse locally (Micc rimmon et al. 2011). However, l arge average dispersal distances (908 km) from natal sites to subsequent breeding sites, and a relatively low philopatry (24%) may indicate a more nomadic strategy (Melvin et al. 1999) Important wintering areas of U.S. bree ders include Florida and coasts of the Mid Atlantic States, Gulf of Mexico, Central America, Bahamas, and Greater Antilles al though some move as far as Colombia (Mikuska et al. 1998). East west movements are apparently unco mmon, and populations breeding i n Atlantic States appear to stay within the Atlantic Coast, Florida, and Caribbean, while banded birds from the M ississippi R iver Basin have been recovered mostly along the northern Gulf into Mexico, Central America, and western Cuba (Byrd 1978 ; Melvin et al. 1999). Banding data has provided information on the distances of movements over large periods of time (months or years) but have not provide d details into the timing or frequency of these movements
46 The a nnual pattern types of movements, and number of movements made by great egret s is interesting from and ecological standpoint, as it provides previously unknown information about a common and widespread species. L ittle is known about this specie s wintering movements and space use despite the critical r ole winter survival plays in driving wading bird population dynamics (Butler 1994 ; Cezilly 1997). Elucidating these details will allow for better interpretations of studies using wading birds as indicators of environmental change ( Kushlan 1993 ; Erwin and C uster 2000 ) and increase our understanding of the interconnectedness of wading bird populations for the management and conserv ation of wading birds ( Boyd et al. 2008 ). This is the first broad scale study of any Ardeid using a robust sample of individuals t racked across seasons. My objective is to identify the movement strategies employed by great egret populations in the southeastern U.S. I provide details regarding long distance movements, particularly the duration timing, and speed of these flights. I al so describe local movements and space use and make comparisons between winter and breeding season ranges Methods Capture and Tagging I used satellite telemetry to study movements individually marked great egrets. T he coastal regions of Louisiana and South Carolina were selected as capture sites These regions are important area s for both winteri ng (Mikuska et al. 1998) and breeding populations. From September 2010 through February 2011, great egrets were captured at daytime foraging and loafing locations u sing a pneumatic net gun fired from a moving automobile ( Meyer et al. in prep ). Birds were aged by tail feather and scapular shape (Pyle 2008). Solar powered ARGOS platform transmitter terminals ( Northstar Science
47 and Technology ) were placed only on after hatch year birds (hereafter, adults) using a Teflon ribbon backpack style harness. Two styles of transmitters were used including ones equip ped with a global positioning system ( Model 22GPS: hereafter GPS ) and traditional transmitters ( Model 12GS: her e afte r PTT) that collected lo cations by measuring the Doppler effect which is the change in transmission frequency emitted by the PTT as detected by the moving satellite (Argos 2011). Total attachment weight was kept to with a mass too low (<875 g) to carry the 35 g GPS package were fitted with the PTT package (26 g) but s o me birds that could have carried a GPS were given a PTT based on availability of transmitters Great egrets were released at their site of capture after a total processing time <60 min. The GPS transmitters were programed to collect 2 locations per 24 h r s : 1 a t 0800 0900 local time and a s e c o n d f r o m 0200 0300 h r s PTT units were duty cycled to collect data over an 8 hour period each day which shifted by a few hours each cycle allow ing operational hours to rotate through a 24 h r clock PTT locations are less accurate ( 1000m) than GPS points ( m) so results from PTT egrets were excluded from fine scale analysis. Data collected from capture through August 15, 2011 was included in the analysis (maximum period of data collection of 11.5 months for any individual). Eigh ty two adult great egrets were fitted with satellite transmitters. LA transmitters (n=41) were deployed in Sep and Oct 2010, followed by SC (n=41) from December 2010 to February 2011. An equal number of GPS and PTT transmitters were deployed (41 each), but more GPS transmitters were deployed in SC than LA (23 vs. 15) due to the delivery schedule from the supplier
48 Home Ranges and Flight Distances I calculated h ome ranges and foraging flight distances of g reat egret s carrying GPS transmitters which report ed 30 daytime locations (Seaman et al. 1999). L ocation s were entered into a g eographic i nformation s ystem ( Arc GIS 9.3 ESRI, Redlands, California ). I used the ABODE extension (Laver 2005) to calculate 90% contours from fixed kernel densities of locations of each individual using a bandwidth determined by least squares cross validation (Worton 1989) I f ound that long, one way movements resulted in an over smoothed kernel and home range size s that w ere not biologically sensible. To remedy this, separate kernel s were calculated for individual s that moved >50 km from its previous location during the study and generated >30 location points This distance was s elected as it was >2 times as far as any egret had flown in a foraging foray Foraging flight distances wer e determined by calculating straight line distance from the night location to the foraging location collected the following day. Distances <30m were excluded as I assumed the egret was attending the roost or breeding colony and not foraging. When comparin g flight distances and home ranges between seasons winter was defined as Sept 1 Mar and the breeding season as 15 Apr 15 Aug. I omitted data collected between 1 March and 15 April when the populations were transitioning from winter to breeding season act ivities I have no independent confirmation of breeding status for any egret so breeding season simply applies to the period when great egret movements are most likely to have been influenced by breeding activity. Both PTT and GPS locations were used to i dentify long distance movements I defined movements > 100 km based on geodesic distances as long distance movements Tr ip speeds ( km/d ) were recorded by comparing distance covered between
49 the last point before a movement and the first point transmitted fr om the apparent destination. Flight s peeds ( km/h ) were estimated for each movement step. Both of these speeds are minimum estimates base d on direct paths between points. Local wind speed and direction was averaged over the time between locations fro m NOAA weather stations located near the origin of the flight path, unless otherwise noted. Statistical Analyses I tested for a difference between average winter foraging flight distances and test. I tes ted for a relationship between the number of locations collected and range size using a linear regression. I compared overall test, and conducted a paired t test to test for an effect of season on home range size for 11 great egrets tracked with GPS transmitters over both winter and breeding season. Results Capture and Telemetry Data Summary Adequate samples for computing home range s and daily flight distances (>30 daytime locations) were collec ted for 30 GPS tagged great egrets. Eighty three percent of the points retained for analysis had reported accuracy error < 26m. N o minimum sampling period was needed to describe long distance movements, but d ata from 14 transmitters w ere received for <14 da ys and are excluded from the following results. On average, the remaining bird s were tracked over 172 days 10.8 SE with locations transmitted on 76.9% of days. Local Movements I measure d the distance from roosts to 2 540 sub sequent foraging locations for 30 GPS tagged great egret s. The longest distance between roost and foraging site
50 recorded by an egret that then returned to the same roost (i.e. was not en route to a new roost) was 22.1 km For birds tagged in LA, birds foraged closer to roosts in winter ( 1 .6 km) than in th e breeding season ( 3.8 km, P= 0.0 0 5 ; Figure 3 1) but there was no difference for the birds tagged in SC ( P= 0.102). H ome range s averaged 53 6 km 2 12 3 SE (range = 0.67 225 1 km 2 ) and did not differ between LA and SC, t ( 28 )= 1.86 P= 0. 073 Wh en broken down by season ( Figure 3 2) variation was high, with the exception of the winter population in LA (n=11) which showed consistently small home ranges averaging 7.9 km 2 2.6 SE. Seasonal ranges were generated from 140 11 SE location points. The 3 s mallest seasonal ranges (<1 km 2 ) were of 2 egrets wintering in LA which appeared to forage almost exclusively along a stretch of canal, and of a sedentary egret in SC during the breeding season which foraged along a tidal creek in an estuary and occasionall y nearby constructed ponds The 2 largest seasonal ranges (>200 km 2 ) were for egrets during the breeding season One in North Carolina in the northern bays of the Albemarle Sound traveled over broad areas of open water between locations. The other was a wi ntering egret in SC which utilized 3 dis crete activity centers 10 20 km apart and a 4 th after a long distance movement south I could construct home ranges in both seasons f or a total of 11 individuals from either state but found no pattern in size change between seasons and no overall difference t (10)=1.35, P= 0.206 T here was no t a significant relationship between home range size and the number of points collected R 2 = 0 005, F ( 32 ) = 0.162 P= 0 69 Long Distance M ovement s I combined GPS and PTT tagged gr eat egret data to identify long distance mo vements by individuals. Within the non breeding season (Sept Feb) data was
51 collected for 63 great egrets for at least 2 weeks, with 41individuals transmitting data on 30 days. Six individuals conducted movements >100 km : 4 birds moved to southern locations while 2 moved inland. Two egrets from LA traveled south to Honduras (Figure 3 2). PTT#100097 was in LA on the afternoon of 4 Nov but 26h 20m later was 925 km south on the Yucatan Peni nsula I received no locations over the Gulf, but the travel time was too short to allow for the >2700 km circum gulf route (e.g. an unrealistic minimum flight speed of >103 km/h ) Average winds (4 4 km/h NNW ) at a weather station in the cent ral Gulf supported the direct flight. The egret continued south and was recorded both over the Caribbean S ea in f avorable winds ( 24 km/h NNW), and in Honduras at 6 Nov 2205 h r s It remained in Honduras until its last transmission on 13 Nov. For t he second egret, GPS#100022, an unusually long 30 day period without transmissions occurred from 23 Nov 22 Dec, during which the bird moved from LA to the La Miskitia region of Caribbean coastal Honduras where it transmitted for 3 more days. GPS#100237 (Figure 3 2) spent 7 27 Dec in SC before a location 360 km to the south and 77 km offshore over the Atlantic Ocean received at 0301 h r s on 28 Dec A weather buoy reported NW crosswinds ( 3 2 k m /h The bird was recorded at Cape Canaveral F l orida the n ext morning through 8 Jan. The 4 th southward movement was of GPS#100235 which moved 10 4 km down the SC coast on 21 Jan, where it stayed 8 days before continuing another 50 km. Two birds mov ed >100 km inland during the winter. PTT#100104 remaine d in SC until 28 Dec By 30 Dec it moved 70km to the southwest where it stayed >8.5 hrs before it continued 150 km, stopping in the interior coastal plain of Georgia by 1 Jan
52 P TT#100070 moved from coastal LA on ~17 Jan to the Atchafalaya Basin. It moved up and down the basin over the next 16 days, traveling up to 155 km from its prior location on the coast. Forty one great egrets ( LA = 13, SC = 28) were followed from the winter into the breeding season. Most of t hese individuals stayed within 4 0 km of their w inter locations (Figure 3 3 ). However, 12 egrets (1 i n LA 11 in SC) relocated >100 km between the winter and breeding season There movements were c o nducted 12 Mar 24 Apr ( mean departure date = 26 Mar ) GPS#100015 from LA traveled 127.9 km on 8 Apr to a l ocation in the Atchafalaya Basin. Most of the 11 long distance migrants from SC moved to locations on the Atlantic coast (Figure 3 4), with the exception of 2: PTT#100317 moved 134 km to North Carolina where it settled 132 km from the coast; GPS#100240 whic h traveled 15 74 km to Michigan (Figure 3 5) GPS#100240 was unique for many reasons : it traveled in an indirect route, made 2 prolonged stopovers ( 5 and 6 days ) crossed the Appalachian Mountains in Pennsylvania, and spent a night on the South Shore of Lake Ontario before initiating a daytime flight westward across Southern Ontario to Michigan. Upon departure, w inds on this westward leg were favorable (24 km/h NNE), but it likely faced headwinds during the second half (18 km/h SW) In addition, 2 egrets cond ucted long distance flights early in the breeding season but quickly returned to their winter locations where they remained into the spring. GPS#100242 departed SC on 29 Mar and traveled over land 3 80 km to St. August ine, FL, transmitting several moving poi nts at night. It stayed no more than 40 hrs but visited a known active breeding colony before returning to SC by 2 Apr PTT#10073 traveled
53 128 km from coastal LA on 2 7 Feb to a forested swamp on the banks of the Mississippi River where it remained for 1 to 3 .8 days. Both birds returned to the same roost area they had used before their trips. Minimum speeds estimated for long distance movements indicated that great egrets at times were traveling at ground speeds >79.9 km/h (Table 3 1). Most migrations were comp leted in under 2 days exemplified by GPS#100250 and 100 236 which traveled >700 km in < 24 hrs. GPS#100240 and 100 248, each made stops totaling 12 & 15 days, respectively. For egrets traveling >300 km, trip speeds averaged 405 km/d 66 SE. Of the 12 birds that conduct ed long distance movements between seasons, 2 individuals returned to their previous winter ranges before the end of the study. GPS#100015 returned on 1 Jun and GPS#100252 returned by 21 Jun The remaining 10 were still on in the vicinity of their breeding season ranges as of 15 Aug. Movement Strategies Individuals from both LA and SC utilized migratory, nomadic, and sedentary movement strategies over the course of the study (Table 3 2) Of the 41 individuals tracked from winter into the breeding season, 19 (46.3%) displayed sedentary behavior maintaining overlapping seasonal ranges in a relatively small area 14 of these individuals were never recorded moving outside of a 15 km radius. Thirteen (31.7%) were migratory, and 9 ( 21.9 %) were nomadic moving betw een multiple distant, non overlapping areas of activity within a season. This included 2 individuals described above (GPS#100242, PTT#100073) which made long distance, exploratory movement s at the onset of the breeding season but r eturned to their prior locations within 5 days.
54 Discussion Local M ovements I found average foraging flight distances during the breeding season (~4 km) that were within the range of those reported at breeding colonies ( 2.8 km 13 .5 km; Thompson 1978; Smith 1995; Custer and Gali 2002 ; Custer et al. 2004 ) Flight distances in the winter in LA were shorter than breeding season This could be explained by breeding egrets being more place bound in terms of roost site as they would have to travel further to foraging sites, rather than move roost location s in response to changing foraging conditions. I know of no other study which has calculated individual ranges for great egrets in any season. Most previous methods of addressing space use for colonial wading birds have relied on flight distances to determine the area of foraging habitat required by colonies, as opposed to individuals (Gibbs et al. 1987 ; Custer et al. 2004). My seasonal range estimates were highly variable, but overall surprisingly small (0.67 220.2 km 2 ). The large varia nces in my size estimates reflect differences in the underlying movement patters utilized (see below). Large seasonal ranges were indicative of nomadic behavior associated with occasional shifts of activity centers within a season. Several birds relied up on a few adjacent wetland features, indicating that some habitats may provide stable resources within a season. I could not identify a difference range between seasons, and across wading bird s pecies there appears to be no consistent trend. S easonal ranges for Black storks in France were similar between breeding and non breeding adults (540 km 2 Jiguet and Villarubias 2004), while great bitterns in Brittan had larger home ranges in winter (0.33 km 2 ) than during breeding season (0.15 km 2 ; Gilbert et al. 2005 ).
55 Egrets wintering in LA had surprisingly small home ranges and foraging flight distances and generally did not make long distance migrations between season s This suggests that the quality of habitat i s high in LA These birds were in an area of abundan t wetlands which accounted for >70% of lan d cover in the region (Chapter 2 Ta ble 2 1), providing a variety of wetland habitat s within a short distance. As t emperature s in the region are rarely below freezing this area can provide potential foraging year round (Frederick and Loftus 1993) Long Distance Movements Great egrets traveled up to 15 00 km from their capture locations. While the capa city for such long distance movement has been known from band recovery programs ( max = 3125 km; Melvin et al. 1999 ) the speed and directionality of flight was poorly understood. Generally, long distance movements were rapid, both in terms of the overall journey and ground speeds. Most flights were direct with locations received during travel in line with origin and des tination, and b ased on time between departure and apparent arrival I infer tha t there were few instances of prolonged stop overs Flights were usually occ urred at night and sometimes ove r great expanses of open water. Herons and egrets use flapping flight for long distance migr ations (Liechti & Schaller 1999; Kushlan and Hafner 2000). When ground speeds could be estimated, I determined velocities as high as >79 km/h based on time between locations (Table 3 1). Average flight speeds of great egrets over shor t distance s have been recorded between 3 5 8 and 38.8 km/h with a maximum of 45.1 km/h ( Custer and Osborn 1978 ; Stolen et al. 2007 ). My reported trip speeds are indicative of assistance from tailwinds Surface winds recorded during flights were typically favora ble but the altitude at which these
56 great egrets were flying wa s unknown. S imilar flight speeds were reported for purple herons (max 80.0 km/h) w hich migrated on average at 700m altitude ( van der Winden et al. 2010). Altitudes reported during the migration of medium sized herons in Israel found use of high altitude winds ( >5000 m ) to maximize travel speed (Liechti & Schaller 1999). My speed estimates could have been reached with the support of surface wind s but these minimum estimates are based on straight line distances and I suspect that maximum speeds were much greater for portions of the flight s. Great egret flight speeds have been shown to be influenced strongly by relative wind direction when compared with other wading birds (Maccarone et al. 2008) so selection of departure day based on wind direction would be advantageous. Long distance movements were direct in terms of flight path suggesting that the birds may ha ve been there before or were traveling with others who had Great egrets may migrate in dividually or in small groups which have been confirmed departing colonial roosts together (C. Weseloh, cited in Miccrimmon et al. 2011). The prolonged stopovers en route to breeding ranges made by 2 individuals (GPS#100240, GPS#100236) may have been visit s to potential breeding sites or refueling stops. Minimum t rip speeds including stop over time averaged >400 km/d for movements >300 km Due to long intervals between locations determining when birds arrived or departed was often not possible within less than a 16 hr window and th erefore trip speed s are certainly underestimated for many individuals. These speeds are impressive when compared to other wading birds. Wood storks in Florida and Georgia moved between season al ranges at an average daily rate of 5 3 km/d (max 184 km/d; Hylton 2004) and s torks migrating from LA to southern Mexico use d a
57 circum gulf route through coastal Mexico over a period of several weeks (Bryan et al. 2008). Similar migration speeds are used by white storks ( Ciconia ciconia ) in Eu rope and Asia ( Van der Bossche et al. 2002 ; Pierre and Higuchi 2004), which took up to 2 months to complete their route. Storks are much heavier than egrets and use thermals to glide during migration and thus would be unlikely to migrate at night or over open water (Kirby et al. 2008) and would be more dependent on weather conditions Pilot studies of purple herons ( Ardea purpurea ) from Europe showed a rapid migration of individuals averaging >600 km/day ( van der Winden 2010). T hese migra n t s crossed vast a reas of inhospitable habitat in the Sahara, so the potential for making stopovers did not exist. In fact, many birds perished along the route in sandstorms suggesting a proximate pressure for the adaption of rapid flight over the area. However, my great e grets traveled at a comparable rate over vast areas of suitable wetland habitat Many herons migrate at night (Liechti a nd Schaller 1999 ; del Hoyo et al. 1992; van der Winden 2010 ), but published reports of migrating great egrets are scarce. They had been considered diurnal migrants (Miccrimmon et al. 2011), though nocturnal migrations were also reported (C. Weseloh, cited in Miccrimmon et al. 2011). In this study, long distance flights were typically conducted at night, but may have continued into the foll owing morning, and segments were occasionally initiated during day (GPS#100240). G reat egrets were known to fly across open ocean based on band recoveries of continental birds on Caribbean islands ( Coffey 1948; Mikuska et al. 1998 ; Melvin et al. 1999 ), and it was hypothesized that the birds may be arriving in the Caribbean via the circum gulf route and shorter open water distance from the Yucatan (Coffey 1948 ; Mc C rimmon et al. 2011). This study confirmed at least one incident of a great egret
58 crossing the c entral Gulf of Mexico (>925 km). A second great egret was confirmed over the Atlantic making a direct flight between SC and Florida cutting across 480 km of open ocean. Movements by great egrets and other Ardeids over open ocean are not unusual off the Flo rida c oast based on incidental sightings made from vessels 6 0 to 1 6 0 km off shore (M. Brothers, personal communication, May 2012) While this does not clarify the route taken to reach Caribbean islands, it certainly increases o ur understanding of the navigatio nal and flight capabilities of this species Different b ird specie s are believed to navigate through a variety of methods including landmark orientation magnetic compass solar compa s s, and celestial aids ( Berthold 2001 ) Reliance on one me thod c ould rest rict m igration capabilities For example, some nocturnal migrants use celestial navigational to migrate ( Emlen 1967 ), which inh ibits their ability to migrate during the day. B oth nocturnal and diurnal migrants may use landmarks for navigation (Berthold 200 1 ) but very few migratory birds appear to transition between nocturnal and diurnal migration ( Liechti and Schaller 1999 ). An open water crossing of the Gulf of Mexico would exclude reliance upon visua l landmarks while a solar compass could not guide noct urnal flights. Coupled with the ability of great egrets to continue to navigate and even begin long distance flights in the day may suggest that the birds are guided by a magnetic compass or are not reliant on a single navigational aid Variety in Movement Strategies Migratory, sedentary, and nomadic individuals existed within the tagged population. Despite the impressive flight capabilities I described above, many of the birds (46.3%) displayed sedentary behavior and remained within the same general locati on over the duration of the study Most of the birds were not tracked long enough
59 to confirm whether the long distance movements observed were regular and round trip and thus migrations However, 6 great egrets did return to their prior winter range s befo re 15 Aug s uggesting that these movements at the onset of the breeding season a re likely migrations. While southward migration of this species has typically been considered a response to lowering temperatures (Miccrimmon et al. 2011) these s outhward retur ns during the warmest months of the year suggest that other motivations are involved. Nomadic behaviors, in this case indicated by movements between separate areas within a season, also suggest alternative factors motivating movement. Most of the captures were conducted within a relatively small geographic area and many egrets used similar habitat types (Chapter 2 ). Why individuals within popul ations responded differently to local conditions is unknown. Individual vari ability in movement strategies in respo nse to the same resources challenges the idea that movement patterns s ( Roshier 2008 ). One explanation could be that b ehavioral differences likely exist between non breeders and breeders within seasons in my populations I could not verify breeding status to confirm this but based on roost locations it appeared that breeding attempts were not limited to birds using a single strategy. I observed a striking difference between LA and SC egrets in terms of the distance traveled between winter and breeding season ranges. Even though migratory ind ividuals existed within both populations, the distance traveled by LA birds was generally short. The farthest distance measured between winter and breeding sites for an egret in LA was ~130 km while 39% of the birds in SC moved over 1 00 km and traveled up to 1574 km en route to breeding season locations. My study area in LA
60 contain ed a higher proportion of wetland habitat than SC and its coastal wetlands comprise one of the most biologically productive ecosystems in the United States (Templet and Meyer Ar endt 1988). Coupled with a lower latitude and slightly warmer climate, LA could support a higher percentage of great egrets as year round residents than SC, as its wetlands may be more predictably higher quality. In addition m y observations may partly be explained by a bias towards capturing non migratory residents in LA produced by a difference in capture dates between LA and SC. S outhward fall mig ration can continue as late as November December in northern states (Miccrimmon et al. 2011) and in LA, great egret numbers increase substantially from November to February (Martin 1985). By Oct 1, 31 of the LA transmitters (75%) were deployed essentially prior to arrival of winter migrants. In contrast, SC captures were conducted Dec Feb t hus exposing many mor e migrants to capture than in LA. Likewise, some birds from the breeding population in SC may have already departed for southe rn locations prior to trapping. Therefore it is difficult to make generalizations about the proportions of these populations util izing different movement strategies from my results Nesting populations of great egret can fluctuate between years by orders of magnitude in regions of the southeast U.S. (Frederick 1995). These changes are too rapid to be explained by local birth and dea th rates and thus emigration and immigration are likely responsible, but how wading birds gain information about conditions at distant patterns to predict conditions els ewhere, or may move solely by chance once local conditions deteriorate. However, this study provides evidence that great egrets can
61 quickly scout distance sites to gain first hand knowledge to inform breeding decision. GPS#100242 traveled to north Florida and visited a known colony before returning to SC; a 4.25 day round trip of 759 km. Similarly, PTT#100073 made a round trip of 256 km up the Mississippi River and back. Summary My findings illustrate the variety of spatial and temporal dynamics of movement behavior s utilized by a common and widespread A rdeid. I confirm ed that g reat egrets ca n move great distances and do so rapidly. Flights were usually direct, timed with local wind conditions, and conducted at night O pen water did not appear to dictate mov ement path s. Great egrets can apparently explore distant locations rapidly al low ing them to make decisions about where to breed and winter based on empirical local information. D espite these capabilities, not all great egrets need to make long distance mo vements and r elatively small areas of high quality habitat can support egrets year round.
62 Figure 3 1. Average distance from nightly roost to subsequent foraging site for great egrets tagged with GPS transmitters in LA or SC. Winter distances were measured during Sep Feb and breeding season from Apr Jun. Error bars represent 95% CI.
63 Figure 3 2. Comparison of 90% kernel ranges between seasons and capture location of great egrets tagged with GPS transmitters. Error bars repre sent 95% CL. Winter includes points collected Sep Feb and breeding season from Apr Jun.
64 Figure 3 3 Southward long distance movements of 3 great egrets during the 2010 2011 winter. Dashed line represents hypothetical route during 1 month period of missi ng data.
65 Figure 3 4. Distances between winter season and breeding season ranges for 41 great egrets tagged during winter in LA (n=13) and SC (n=28). Connecting lines are shortest distance paths, not flight paths.
66 Figure 3 5. Long distance northward movements between winter and breeding season by three great egrets.
67 Table 3 1. Distance and speeds for long distance flights (>300 km) of satellite tagged great egrets. Flights missing >1 day of data excluded. Travel Time is maximum duration of trip includ ing stopovers, while speeds and distances are minimum estimates based on shortest geodesic distance between points. Segment Speed is the greatest speed calculated for movement steps on each trip, and winds data is for the same segment (NOAA). Note #100242 & 100252 conducted round trips. Bird ID Departure Travel Time (days) Travel Distance (km) Trip Speed ( km/d ) Segment Speed (km/h) Wind Speed (km/h) Relative Wind Type PTT#100097 11/4/2010 2.34 1586.8 677.9 79.9 24.0 Tailwind GPS#100240 3/29/2011 14.64 15 74.3 107.5 50.6 24.2 Tailwind GPS#100250 4/4/2011 0.94 876.8 876.8 64.5 32.2 Tailwind GPS#100236 4/3/2011 0.52 708.9 708.9 61.2 7.6 Tailwind PTT#100099 4/11/2011 1.11 685.3 614.8 25.6 16.4 Tailwind GPS#100251 4/11/2011 2.04 612.5 299.8 43.3 20.3 Tailwi nd PTT#100308 4/23/2011 1.17 503.5 431.5 18.0 11.4 Tailwind GPS#100246 3/21/2011 3.14 476.9 152.1 19.5 15.1 Tailwind GPS#100237 12/27/2010 0.85 474.2 474.2 25.9 34.8 Crosswind GPS#100252 3/12/2011 0.30 427.3 427.3 59.5 13.2 Tailwind GPS#100248 3/17/20 11 17.98 423.8 23.6 30.7 2.4 Crosswind GPS#100252 6/20/2011 0.54 383.6 383.6 29.4 7.4 Crosswind GPS#100242 3/31/2010 2.00 379.7 189.8 56.0 3.2 Tailwind GPS#100242 3/29/2011 1.25 379.1 303.2 44.6 17.7 Tailwind
68 Table 3 2. Movement strategies employed b y great egrets followed over both the winter and breeding season and the proportion of the population utilizing each strategy. Strategy Definition Observation Prevalence (n) Example Sedentary Remaining in a single area year round Overlapping seasonal ran ges n ever mov ed outside of a 30 km radius 46.3 % (19) Migratory Conducting regular, round trip movements between seasonal ranges Conducted round trip movements between 2 seasonal ranges 31.7 % (13) Nomadic Conducting irregular and unpredicta ble movements Mov ed between non overlapping, separate areas within a season 21.9 % (9)
69 CHAPTER 4 C ONCLUSION In this study, I successfully followed individually marked great egrets using satellite tracking. This study demonstrated that satellite t elemetry backpacks can be used on great egrets, and that this method is likely the only logistically feasible way to track this species throughout its annual movements given the distances traveled by some individuals. In Chapter 2 I found that some great egret population s were selectin g constructed pon ds and agricultural wetlands over natural habitat at local scales These populations may be supported to a significant extent by these features, particularly in agricultural regions of LA where t he pulse of food during the draining of crayfish ponds coincid e d with the nestling period Current trends in land cover change will ultimately lead to more constructed wetlands and fewer functional natural wetlands My findings in addition to data from current popula tions of wading birds which persist in areas where natural wetlands have nearly all been lost ( Fasola and Ruiz 1 996 ; Fasola et al. 1996 ), indicate that some constructed wetlands can become important habitat and should be considered in future management pla nning. However, e xposure to structural hazards, disease, and toxins may be elevated in ponds and agricultural areas as pesticides, herbicides, and run off can affect wading bird health (Parsons et al. 2010). The seriousness of these risks will vary dependin g upon land use and agricultural practices which can vary from region to region and farm to farm. This study indicates that t here is a need for future research into the relationship between both agricultural wetlands and constructed ponds to wading bird mo rtality and reproductive success in the southeastern U.S.
70 There was no indication that nation al populations were currently reliant upon these constructed wetlands. Broad scale movements of satellite tagged birds did not appear to be influenced by the pres ence or absence of constructed habitats. Dense areas of agricultural wetlands exist not only in Louisiana, but in Florida, Texas, Arkansas, and to a lesser extent in other southeastern states, but these areas were not incorporated into the annual movements of any of the tracked egrets. In C hapter 3 I identified larg e variation among individual movement strategies. Great egrets from the same wintering population appeared to utilize migratory, nomadic, and sedentary strategies. Great egrets proved capable of making extremely fast and direct flights of hundreds of kilometers both within and between winter and breeding seasons. On several instances, egrets returned to prior locations after traveling hundreds of km. Great egrets appear the have the ability not o nly to orient themselves for long distance flights but possess true navigational capabilities to arrive at predetermined destinations. Flights crossing the Gulf of Mexico and out over the Gulf Stream indicated that the birds were navigating in a manner oth er than landmark recognition. Despite this capacity for long distance flight m any individuals remained within surprisingly small areas of habitat throughout the study This suggest s that relatively small areas of high quality habitat can support great egr ets year round. The different responses to similar conditions suggest that great egret may be conducting some long distance movements for proximate reasons other than food availability. Some great egrets likely leave suitable habitat at the onset of the br eeding season to find suitable nesting sites or mates. Movements conducted during the winter may have
71 been in response to density dependent factors related to the arrival of egrets from northern regions resulting in increased competition. These findings no t only increase our understanding of the ecology of this species, but they provide some of the only detailed movement and habitat selection information for any heron or egret species at broad spatial and temporal scale s It provides us with knowledge regar ding the range of movement strategies incorporated by a single species and should thus be informative for study designs an d conservation actions focused on Ardeid populations.
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82 BIOGRAPHICAL SKETCH Jason C. Fidorra was born in Erie, Pennsylvania. He received his B.S. from Allegheny College in e nvironmental s cience and then began pursuing a career in vertebrate conservation and research. He worked with a variety of endangered taxa including wood warblers, shri kes, sea turtles, and honeycreepers before applying for an advanced degree at the University of Florida He was awarded a teaching assistantship through the Department of Wildlife Ecology and Conservation, as well as the Jennings Scholarship for academic p erformance and professional potential. He is expected to receive his Master of Science degree in August 2012.