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Title: Ecology of the Florida sandhill crane
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Title: Ecology of the Florida sandhill crane
Series Title: Nongame technical report - Florida Game and Fresh Water Fish Commission ; 15
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Publication Date: 1997
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Table of Contents
    Copyright
        Copyright
    Front Cover
        Front Cover
    Title Page
        Title Page 1
        Title Page 2
    Table of Contents
        Table of Contents
    Acknowledgement
        Acknowledgement
    Main
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
    Bibliography
        Page 17
        Page 18
        Page 19
        Page 20
    Back Cover
        Page 21
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ECOLOGY OF THE FLORIDA SANDHILLCRANE
N.I.... .rr \\ ii ,[ r TECHNICAL REPORT NO. 15


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ECOLOGY OF THE FLORIDA SANDHILL CRANE


Nongame Wildlife Technical Report No. 15






Beth Stys












Office of Environmental Services
Florida Game and Fresh Water Fish Commission
620 South Meridian Street
Tallahassee, Florida 32399-1600


July 1997


UNIVLKfllI ) i ILko&Uf LAifLlX~t.AL



















SCIENCE
LIBRARy


















Suggested citation:

Stys, B. 1997. Ecology of the Florida sandhill crane. Florida Game
and Fresh Water Fish Commission, Nongame Wildlife Program
Technical Report No. 15. Tallahassee, FL. 20 pp.


Cover photograph taken by Steve Nesbitt






ECOLOGY OF THE FLORIDA SANDHILL CRANE STYS




TABLE OF CONTENTS

ACKNOWLEDGEMENTS ................................. iv

INTRODUCTION ........................................1

LIFE H ISTO RY ........................................ 2

D description .........................................
Range and Habitat ...................................2
Diet ............................. .............. 4
Social Organization ..................................4
Nesting ........................................ 5
Young Birds ........................................6
B behavior ........................................ 7
Response to Disturbance .............................. 7

POPULATION DYNAMICS ................................ 8

Reproduction ....................................... 8
M ortality ........................................ 8
Home Range Size ................. ............... 9

HABITAT REQUIREMENTS ............................ 10

Nesting .............. ......... ...... 10
Foraging .......................................... 11

SURVEYING FOR SANDHILL CRANES .................... 12

MANAGEMENT CONSIDERATIONS ....................... 14

Wetland Habitats .................................. 14
Upland Habitats ................. ..... ............ 14
Response to Disturbance Nesting Season ............... 15
Cranes and People .................................. 15

LITERATURE CITED ................................. 17





NONGAME WILDLIFE PROGRAM TECHNICAL REPORT


ACKNOWLEDGEMENTS


The preparation of this technical report involved the help of many individuals
within and outside of the Florida Game and Fresh Water Fish Commission.
Improvements to the text and information presented in earlier drafts were
made by Brad Hartman, Brian Barnett, Randy Kautz, Mike Allen, Rick
McCann, Mary Ann Poole, Kim Dryden, Brian Millsap, Don Wood, Steve
Nesbitt, Larry Campbell, Marty Folk, David Cobb, Jim Layne, Brian Toland,
Mary Bishop, Peter Merritt, and David Sumpter. Steve Nesbitt and Brian
Toland graciously contributed photographs.






ECOLOGY OF THE FLORIDA SANDHILL CRANE STYS


INTRODUCTION

The Florida sandhill crane (Grus canadenis pratensis) is one of
Florida's most recognizable birds. It stands almost 4 feet tall, and its call is a
unique trumpeting rattle. It uses a mosaic of wetland and prairie habitats in
peninsular Florida south of the Aucilla River, nesting in herbaceous wetlands
and foraging in open prairies, improved pastures, and wetland habitats.

The long-term survival potential of the Florida sandhill crane is at risk
due to the increasing rate of habitat loss or modification, small population size,
and low reproductive potential (i.e., small clutch size, low recruitment rate,
seasonal nesting). Habitat loss from filling or draining of wetlands, degrada-
tion or loss of prairie and range habitats, and fragmentation of remaining habi-
tat into patches too small or too isolated to be suitable for sandhill crane use are
the most serious problems facing Florida's population of sandhill cranes.
Habitat fragmentation and human disturbances may force sandhill cranes to
temporarily or permanently abandon the areas they inhabit, and may reduce the
overall fitness of sandhill crane populations by forcing cranes to travel greater
distances to find foraging and roosting sites. In recognition of these factors,
the Florida Game and Fresh Water Fish Commission listed the Florida sandhill
crane as a threatened species in 1974 (FGFWFC 1996).

Loss of habitat has resulted in an increasing number of cranes using
suburban and urban areas. In addition to their natural habitats, sandhill cranes
can be found in such places as golf courses, airports, suburban subdivisions,
sod farms, beef and dairy cattle farms, and horse farms. Appropriate manage-
ment on the remaining public and private lands where sandhill cranes exist will
enhance their long-term chances of survival in Florida.

This document is intended to provide accurate information on the biol-
ogy and habitat requirements of Florida sandhill cranes. From this information
public land managers and private landowners should be better equipped to
manage their lands for sandhill cranes or to predict how their land use practices
may affect sandhill cranes. This information should prove useful to anyone
who desires to maintain or enhance sandhill crane populations or their habitat.





NONGAME WILDLIFE PROGRAM TECHNICAL REPORT


LIFE HISTORY

Description

The Florida sandhill crane
is a heavy-bodied bird with a char-
acteristic bustle-like arrangement
of tail feathers (Figure 1). It is a
long-necked, long-legged bird,
standing approximately 3.9 ft (1.2
m) tall. Adult sandhill cranes are
uniformly grayish-brown with a
white cheek patch and a red
unfeathered crown. The sexes are
identical in appearance, with the
adult male slightly larger than the
female. At a distance, sandhill
cranes can be mistaken for great
blue herons (Ardea herodias), but
upon closer examination the
crane's reddish crown will distin-
guish it from the great blue heron.
Sandhill cranes fly with both their
neck and legs extended (Figure 2).
The call of the sandhill crane is a
remarkable trumpeting rattle sound Figue 1. Adult Florida sandhill cran. Photo
that can often be heard up to two- by Brian Toland
miles away.



.- Range and Habitat

The Florida sandhill crane
~r anges throughout the Florida penin-
sula from the Okefenokee Swamp,
Georgia, to the Everglades (Figure 3).
However, it is scarce in Monroe and
.:. Dade Counties and is rare west of
Alachua County (Williams 1978).
The Florida sandhill crane is one of
six subspecies of sandhill crane (Grus
Figure 2 Sandhill cranes m flight canadensis). Only one other sub-






ECOLOGY OF THE FLORIDA SANDHILL CRANE


species of sandhill crane
occurs regularly in
Florida. The greater
sandhill crane (G. c. tabi-
da) is a wintering migrant
in Florida, arriving in
north Florida during
October and November
and beginning spring
migration in late February
(Williams and Phillips
1972). While the two
subspecies cannot be dis-
tinguished from one
another in the field, sand-
hill cranes observed in
Florida between May and
September can be
assumed to be the Florida
subspecies. Population
estimates of the Florida Figure 3. Range of the Florida sandhill crane. Data from
sandhill crane range from the Florida Atlas of Breeding Birds.
4,000 to 6,000 individuals
(Tacha et al. 1992).

Florida sandhill cranes are typically found in wide-open prairies
(Walkinshaw 1973). Water depth and seasonal food availability are the prima-
ry factors controlling seasonal shifts in habitat use (Bennett 1992). Large areas
of open water and areas of dense or woody vegetation are not usually consid-
ered suitable sandhill crane nesting or foraging habitat. The majority of sand-
hill cranes in Florida spends much of the year feeding in a variety of upland
habitat types including improved pasture, open pine forests, and agricultural
croplands (Walkinshaw 1949, 1973; Layne 1981, 1983). In south and central
Florida, cranes nest in shallow freshwater marshes and forage on cattle ranch-
es, horse farms, and sod farms. In extreme south Florida, most nests are built
in freshwater marshes near the transition zone between inland marshes and
coastal mangrove swamps (Kushlan 1982).

At night, sandhill cranes roost in shallow herbaceous wetlands. Roost
sites are characterized by standing water 4-12 inches (10-30 cm) deep sur-
rounded by deeper water or large expanses of marsh (Tacha et al. 1992). Roost
site selection is dependent upon seasonal water levels. Roost wetlands can be
limiting in the dry season. During hot weather, sandhill cranes will use forest-


STYS 3






NONGAME WILDLIFE PROGRAM TECHNICAL REPORT


ed edges of forest-pasture transition (Nesbitt and Williams 1990) or emergent
herbaceous wetlands for midday loafing (Bishop 1988).

Florida sandhill
cranes are increasingly
becoming residents of sub-
urban areas, and even
select areas in urban set-
tings (e.g., golf courses,
airports) (Figure 4). It
appears that sandhill cranes
can become acclimated to
living in close proximity to
people. Types of devel-
oped lands that can provide
suitable habitat for sandhill
cranes include horse farms,
cattle farms, sod farms,
nature trail areas, golf
course roughs, and other
types of development that
retain grasslands and small Figure 4 Pair ofFlorida sandhill cranes nesting in a
herbaceous wetlands. small wtland on a small airport. Photo by Brian Toland

Diet

Sandhill cranes are opportunistic feeders. Their diet includes such
items as aquatic invertebrates and plants, insects, worms, seeds, grass shoots,
grains, bulbs, berries, lichens, small mammals, and birds. Sandhill cranes
scratch with their feet or probe with their bill to unearth underground food
items. In central Florida, sandhill cranes have been observed eating fruit and
tubers from nut grass (Cyperus spp.), blueberry (Vaccinium myrsinites), and
huckleberry (Gaylussacia duniosa) (Walkinshaw 1976), as well as acorns from
live oaks (Quercus virginiana) (Bishop 1988). Additionally, sandhill cranes
will feed on agricultural crops, especially corn and peanuts (Nesbitt 1996).

Social Organization

Sandhill crane populations can be divided into three primary social
units: (1) unpaired subadults and adults, (2) mated pairs, and (3) famihes. They
also are often classified into groups based on their age: juvenile, less than one
year of age; subadult, one to three years of age; and adult, greater than three
years of age (Nesbitt and Williams 1990). Families, which consist of a mated






ECOLOGY OF THE FLORIDA SANDHILL CRANE STYS


pair and juveniles, will often forage in close proximity to other cranes or share
the same roost (Bishop 1988). Juveniles remain with their parents until ten
months of age (Nesbitt 1992). When families break up in the spring, first-year
juveniles join or assemble into non-breeder flocks, usually of two to five
cranes, which remain together for up to one year (Nesbitt and Wenner 1987).
It is in these non-breeder flocks that initial pair bonds are often formed (Nesbitt
and Wenner 1987).

Subadult pairings are often ephemeral, with most birds pairing several
times before establishing a persistent bond. The successful production of
young is usually related to the establishment and duration of a pair bond
(Nesbitt and Wenner 1987, Nesbitt 1989). Established pairs are perennially
monogamous, having a pair bond that is persistent even during the non-breed-
ing season (Walkinshaw 1973, Nesbitt and Wenner 1987). Re-pairing usually
occurs after the death or disappearance of a mate (Nesbitt and Wenner 1987).
An unpaired adult crane without a territory often will join the juvenile/non-
breeder flock, soon thereafter pairing with a new mate.

Nesting

Nest initiation is influenced by the amount of water in nesting ponds,
and the amount and timing of rainfall during the prenesting and nesting seasons
(Walkinshaw 1976, Bishop 1988). Rainfall amounts in January-March can
explain almost all (97%) variation in the number of pairs with young. High
winter rainfall increases productivity by creating suitable water depths for nest-
ing and by improving feeding conditions. On the other hand, high rainfall
amounts in early spring may reduce productivity due to flooding of nest sites
(Layne 1983). Sporadic use of specific nesting areas should be expected due
to the highly variable nature of suitable water conditions for sandhill crane
nesting. Non-use of a wetland site during one or more nesting seasons should
not be interpreted as abandonment of an area.

Nest initiation for Florida sandhill cranes can begin as early as
December, but usually begins in January (Walkinshaw 1973) and can extend
through August (Bent 1926). In south central Florida, average laying dates are
22 to 24 February (Walkinshaw 1982), while 3 March is the average laying
date in north central Florida (Tacha et al. 1992). After the loss of eggs or
chicks, sandhill cranes will renest. Florida sandhill cranes have been docu-
mented-renesting up to three times per year, with 19.5 days the average inter-
val between loss of clutch and laying of new eggs (Nesbitt 1988).

Average clutch size for Florida sandhill cranes ranges between 1.72
and 2.0 eggs (Walkinshaw 1949, 1973, 1976, 1979, 1982; Thompson 1970;






NONGAME WILDLIFE PROGRAM TECHNICAL REPORT


Layne 1983; Nesbitt 1988; Dwyer and Tanner 1992). Clutch size is not affect-
ed by laying date or clutch sequence (Nesbitt 1988). Incubation begins the day
the first egg is laid and is almost continuous until hatching (Walkinshaw 1976).
Incubation lasts 29-31 days, with eggs usually hatching one day apart
(Walkinshaw 1976). Both the male and female incubate the eggs (Walkinshaw
1985, Nesbitt 1988). Length of the nesting season varies by location, with the
Kissimmee Prairie nesting season lasting approximately two months longer
than the nesting season in northern Florida and Okefenokee Swamp (Bishop
1988).

Young Birds

Sandhill cranes are precocial; the young can run and swim when one
day old. Within the first week the young accompany the adults up to 0.25 miles
(0.4 km) from the nest site into drier pasture habitat to forage (Walkinshaw
1976, Layne 1981), and by 1.5 months old the young are traveling up to 0.30
miles (0.5 km) from the nest site to forage (Layne 1981) (Figure 5). Adults
feed the young until the
young reach approxi-
mately three to four
months of age (Layne
1981). Adult cranes often
construct accessory nests
that are used as rest sites I
by the young during the
day and for brooding the
young at night (Layne
1981). Most accessory
nests are located within -
160 ft (50 m) of the origi-
nal nest, varying with Figur 5. Family of Florida sndill andhill cranes traveling to
proximity of adjacent uplandforaging habitat. Photo by BrSan Toland
suitable habitat.

The young are capable of extended flight at 80-108 days of age
(Walkinshaw 1976, Layne 1981, Nesbitt 1992). Juvenile cranes become indc-
pendent at eight to ten months of age (248-321 days of age, mean 295) (Nesbitt
1992). At 10-14 months of age, the juveniles have an adult-like appearance
(Lewis 1979). First nesting attempts have been recorded for two-year old
males and three-year old females, however, the earliest age of first production
(i.e., fledgling of young) occurs at three years of age for both sexes (Nesbitt
1992). The mean age of first production is 5.2 years of age for both sexes
(Nesbitt 1992).






ECOLOGY OF THE FLORIDA SANDHILL CRANE -STYS


Behavior

Sandhill cranes are very social and often territorial birds, and thus have
many postures and movements that communicate aggression, submissiveness,
and courtship (Tacha 1988). Behavioral displays can provide clues to the
social status and reproductive stage of sandhill cranes. Additionally, several
behaviors are exhibited when a crane is aware of possible disturbance factors.
When alarmed, sandhill cranes will stand rigidly erect with the body nearly
vertical and the head elevated. This position appears to deliver the message
that danger is near. Tacha (1988) described two alert behaviors; seven agonis-
tic behaviors, four of which were aggressive displays; and eight courtship dis-
plays, three of which were limited to pairs, and the remainder of which were
exhibited by all social classes. Many of the behaviors are also described by
Vos (1977), and Nesbitt and Archibald (1981), with perhaps slightly different
names.

Response to Disturbance

Although cranes will tolerate some human activity, even becoming rel-
atively tame in some instances, they prefer large, open spaces with minimal
disturbance (Bishop 1992). In particular, disturbances in and around wetlands
with a nest can have a great impact because breeding pairs usually remain in
the vicinity of the nest wetland during both the nesting and pre-fledgling peri-
od (Bishop 1992). Nesting by sandhill cranes can be deterred or interrupted
due to disturbance. If sandhill cranes feel that the source of disturbance is a
potential threat, they may leave the area. Nesting cranes flush when people
approach within 10 to 250 ft (3 to 75 m) of the nest, and, once flushed, the birds
remain off the nest for 15 minutes to three hours (Dwyer and Tanner 1992).
Each pair of sandhill cranes and each nesting occurrence is unique, and indi-
vidual cranes may react to disturbance differently. Such disturbances may not
be severe enough to cause nest abandonment, but they may interrupt and thus
extend incubation activity (Toland 1991, 1993). Incubation periods extended
for even two days can lower hatchability or nestling survival rates. Success
rates and recruitment levels of Florida sandhill cranes nesting in some devel-
oped areas may be below the level needed to compensate for natural and unnat-
ural mortality (Toland 1991, 1993). However, if a source of disturbance is in
place when sandhill cranes move into the area, the cranes may accept the dis-
turbance as part of their nesting environment and remain throughout the nest-
ing season.





NONGAME WILDLIFE PROGRAM TECHNICAL REPORT


POPULATION DYNAMICS

Reproduction

Hatching success rates range from 39 to 88 percent (Thompson 1970,
Walkinshaw 1982, Nesbitt 1988, Bennett and Bennett 1992, Dwyer and Tanner
1992). Average brood size ranges from 1.14 to 1.59 chicks (Layne 1983,
Bishop 1988). The probabilities of survival from hatching to fledgling, hatch-
ing to independence, and fledgling to independence are 0.65, 0.57, and 0.87,
respectively (Nesbitt 1992). The percentage of juveniles in the population
ranges between 6.0 and 11.1 percent (Bishop 1988, Bennett and Bennett 1990,
McMillen et at. 1992, Nesbitt 1992). Lifetime reproduction is estimated at
1.86 young for any adult (Nesbitt 1992) and 2.70 young for an established
breeder (i.e., an adult that has reproduced successfully at least once) (Tacha et
al. 1992).

Mortality

Causes of nest failure include predation, flooding, abandonment, and
egg infertility and addling (Dwyer and Tanner 1992). Flooding is the major
cause of egg loss in north central Florida (McMillen et al. 1992). Egg and nest
predators include raccoons (Procyon lotor) and fish crows (Corvus ossifragus)
(Dwyer and Tanner 1992). Occasionally, eggs or chicks are lost to feral hogs
(Sus scrofa), river otters (Lutra canadensis), red-tailed hawks (Buteojamaicen-
sis), great-homed owls (Bubo virginianus), and American alligators (Alligator
mississippiensis) (Dwyer and Tanner 1992). Although predation by coyotes
(Canis latrans) is minimal, they may become an important predator as their
population expands in Florida (Nesbitt and Badger 1995).

Sandhill cranes are normally long-lived, up to 20+ years (Tacha et al.
1992). Adults have few natural enemies, occasionally falling prey to bobcats
(Felis rufis) or bald eagles (Haliaeetus leuccocephalus) (Nesbitt 1996). Avian
botulism (Clostridium botulinum), avian cholera (Pasteurella spp.), and avian
tuberculosis (Mycobacterium avium) have been reported in sandhill cranes in
Arizona, Nebraska, and Colorado (Windingstad 1988). Moldy corn and waste
peanuts have been the suspected sources of mycotoxins in several sandhill
crane die-offs in Texas (Windingstad 1988). Lead poisoning has been respon-
sible for several sandhill crane deaths in Colorado and Nebraska (Windingstad
1988).

Sandhill cranes are vulnerable to man-made hazards such as power
lines and fences. In most power line mortality cases, death is caused by colli-
sion with the power line, resulting in broken necks, wings, and legs, and mul-






ECOLOGY OF THE FLORIDA SANDHILL CRANE -STYS


tiple fractures (Windingstad 1988). Fences in areas of suitable foraging habi-
tat pose a great danger if cranes cannot walk under or pass through the fence.
Cranes may sometimes misjudge the distance to a fence or the height of a fence
and may collide with it when attempting to land, often resulting in broken
bones and death (Nesbitt 1996). Free-ranging dogs and cats can cause reduced
reproductive success by preying on eggs and young, as well as by lowering
crane use of an area. Sandhill cranes may avoid areas where free-ranging dogs
or cats are present (Nesbitt 1996).

Cranes with pre-
fledged young run a
higher risk of being
struck by a vehicle.
Adults with pre-fledged
young will walk across
roadways rather than fly,
increasing their chances
of being struck by a vehi-
cle (Figure 6). Several
cranes in south Florida
have been killed or
injured due to collisions
with vehicles or airplanes
when foragg in areas Figure 6 Fail ofFlorida sandhill cranes walking across
adjacent to highways and a road Photo by Brian Toland
runways (K. Dryden,
personal communica-
tion).

Home Range Size

Home range size varies seasonally and regionally. In north central
Florida, sandhill cranes had home range sizes of 625 acres (253 ha), 445 acres
(180 ha), and 306 acres (124 ha) during the prenesting, nesting, and postnest-
ing seasons, respectively (Nesbitt and Williams 1990). Paired adults on the
Kissimmee Prairie had a mean annual home range size of 452 acres (183 ha)
(Bishop 1988). Although home range size varies seasonally, there is much
overlap in habitat use during the different seasons. Florida sandhill cranes do
not have distinct winter, spring, or summer home ranges, but rather exhibit a
slight shifting in home range size based on their current needs and location of
suitable habitat. Subadult home range size averages 4 to 10 times larger than
adults (Bishop 1988, Bennett 1989a, Nesbitt and Williams 1990).






NONGAME WILDLIFE PROGRAM TECHNICAL REPORT


Sandhill cranes in Florida defend nest sites and adjoining wetland
habitats during the breeding season (Walkinshaw 1973); however, they may
abandon their territories in late summer and become social (Walkinshaw 1973,
Layne 1981, Nesbitt 1996). In central Florida, some pairs tend to remain social
year-round, often with several pairs nesting in a single wetland as small as 13.5
acres (5.46 ha) (Bishop 1988). Social behavior may be important to cranes that
follow a daily pattern of commuting between wetlands and uplands for feed-
ing, and to populations that occupy small or ephemeral wetlands that cannot
support cranes throughout the year (Nesbitt and Williams 1990).


HABITAT REQUIREMENTS

Nesting

Nest habitat selection is
strongly influenced by water
regimes and habitat availability,
both of which are highly vari-
able over time. Due to this vari-
ability, sandhill crane nesting
habitat and nest site location
often change from year to year.
Nesting habitat used by Florida
sandhill cranes also varies
regionally. In north central,
central, and south west Florida,
sandhill cranes typically nest in
mixed persistent and nonpersis-
tent freshwater herbaceous
wetlands with maidencane
(Panicum hemitomon), pick-
erelweed (Pontedaria cordata),
smartweeds (Polygonum spp.),
and rushes (Scirpus spp) as the
dominant wetland vegetation
(Walkinshaw 1976, Nesbitt and
Williams 1990, Depkin et al. Figure 7 Florida sandhill crane nesting m herba-
1994) (Figure 7). In south ceous wetland vegetation. Photo by Brian Toland
Florida, cranes typically nest in
open slough areas of wet prairies and in freshwater marshes (Thompson 1970,
Kushlan 1982). At 65% of the south Florida nest sites there was little to no
vegetation. The remaining nests were located in areas dominated by maiden-






ECOLOGY OF THE FLORIDA SANDHILL CRANE STYS


cane and pickerelweed (Thompson
1970) (Figure 8).

Mean water depth at nest
sites ranges from 5.3 to 12.8 inches
(13.5 cm to 32.6 cm); although
water depth at the nest site is highly
variable, depending on weather
conditions during the nesting period
(Thompson 1970, Walkinshaw
1976, Dwyer 1990, Bennett 1992).
Nesting of sandhill cranes on dry
prairies has been noted by Holt
(1930), Walkmshaw (1976), and Figure 8. Florda sandhll crane nest in south-
Layne (1982) and has been ern Flortda. Note the sparse vegetaton sur-
observed on a golf course (B. wounding the nest Photo hy Brian Toland
Toland, personal communication).
Nests are usually 15.7 to 57.1 inches (40 to 145 cm) in diameter (Bennett 1992)
and are usually 4 to 6.3 inches (10-16 cm) above the water surface (Tacha et al.
1992). Distance between simultaneously active nests of two different pairs
ranges from 236 ft (72 m) to several miles, and the average distance between
same-season renestings is 600 ft (183 m) (Dwyer 1990). There are often mul-
tiple simultaneous nestmgs with wetlands, with up to six pairs recorded in a
212-acre (86 ha) wetland (Dwyer 1990). Although the cryptic coloration of
sandhill cranes makes them difficult to observe, their nests are usually large
and conspicuous and can be located during aerial surveys (Bishop and Collopy
1987, Bishop 1988, Bishop et al. 1991).

Foraging

Throughout central Florida, resident sandhill cranes spend much of
their time foraging in uplands consisting of improved pasture interspersed with
cabbage palm (Sabal palmetto), pines or oaks; live oak hammocks (Quercus
virginianus); open pine forests; herbaceous wetlands; and agricultural crop-
lands (Walkinshaw 1949; Layne 1981, 1983; Bishop 1988). Improved pasture
is the most frequently used daytime habitat, followed by herbaceous emergent
wetlands. Croplands and plowed pastures are used seasonally (Bishop 1988).
On the Kissimmee Prairie, much of the best sandhill crane foraging habitat is
located on large, privately owned cattle ranches (Layne 1981). Suitable upland
habitat for sandhill crane foraging needs to have a majority, or can be managed
to have a majority, of the vegetative cover in the area equal to or less than 20
inches (0.5 m) in height. During the pre-fledgling period, herbaceous emergent
wetlands are one of the most commonly used foraging habitats (McMillen et






NONGAME WILDLIFE PROGRAM TECHNICAL REPORT


al. 1992). However, sandhill crane use of wetland habitats for foraging is lim-
ited by water depth, with cranes rarely foraging in water that is greater than
hock-deep (S.A. Nesbitt, personal communication). In north central and cen-
tral Florida, some of the important habitats used by sandhill crane families dur-
ing the pre-fledgling period are improved pasture supporting Cynodon dacty-
lon or Paspalum notatum; herbaceous emergent wetlands dominated by sedges
(Carex spp), pickerelweed, maiden-cane, and beggar-ticks (Bidens spp.); and
marsh/pasture transition zones vegetated by maiden-cane, rushes (Juncus spp.),
and spikerush (Eleocharis spp.) (McMillen et al. 1992).


SURVEYING FOR SANDHILL CRANES

Before implementing any type of management actions for sandhill
cranes, several questions should be answered. First, are cranes using the area
in question? If so, what types of areas and specific locations are they using,
and what part of their life history needs (i.e., reproduction, foraging, roosting)
are being met on site? A general knowledge of the area's habitat types will
make answering these questions quicker and easier. The time of year cranes
are observed, the number of cranes observed, and the habitat types the cranes
are observed in can be used to help determine the extent of crane use of the sur-
veyed area. A pair of cranes observed in close proximity to wetland habitat
during the breeding season is most likely using the area for nesting and forag-
ing. Additionally, a lone crane observed during the nesting season should be
assumed to be nesting and its mate is on the nest (M. Folk, personal commu-
nication). A group of cranes observed during any time of the year is most like-
ly using the area for foraging. Cranes observed entering a wetland area in the
evening and leaving the area in the morning are most likely roosting within the
wetland.

Surveys can be conducted to determine if cranes are using the area and
where they are, and possibly which of their needs are being met. Surveys
should be conducted in areas of suitable sandhill crane habitat. The following
habitat types (Florida Dept. of Transportation 1985) are considered suitable for
sandhill cranes with the italicized types representing those which are most fre-
quently used for nesting: cropland, fallow cropland, pastureland, sod farms,
horse farms, herbaceous rangeland, mixed rangeland, shrub and brushland,
hydric pine flatwoods (cypress-pine-cabbage palm), shorelines, inland ponds
and sloughs, freshwater marshes, wet prairies, emergent aquatic vegetation,
and intermittent ponds. Suitable upland habitat is dominated by vegetation
equal to or less than 20 inches (0.5 m) in height. Dense, brushy vegetation is
not considered suitable. Suitable wetland areas are relatively shallow, with
normal water depths ranging from 0 to 32 inches (0 to 80 cm). Large areas of







ECOLOGY OF THE FLORIDA SANDHILL CRANE STYS


open water and areas dominated by dense vegetation are usually not suitable
for sandhill crane nesting.

If the amount of suitable sandhill crane habitat is small, ground sur-
veys are probably the best survey method. Due to the often elusive nature of
sandhill cranes, surveyors may want to initially approach the site quietly and
scan the area from as far away as possible. Surveys on small areas can be con-
ducted by selecting an observation point from which the area can be viewed
completely. An observation point will reduce the chance of disturbing the
birds, if they are present on the area. If the area is large (i.e., cannot be viewed
from one observation point) surveys can be conducted by vehicle, boat, foot,
or horseback. For best possible coverage, transect surveys should provide as
close to 100% coverage of all suitable sandhill crane habitat as possible. The
distance between transects should be spaced according to the limits on visibil-
ity imposed by vegetation and terrain. Ground surveys and nest searches con-
ducted during the active nesting season should be done during the cool part of
the day (dawn 1000 hr, and 1600 hr dark) to avoid flushing the cranes from
the nest and leaving the eggs exposed during the hot part of the day (S.A.
Nesbitt, personal communication).

For large areas containing suitable sandhill crane habitat, surveys are
often completed by conducting aerial transects. Although the cryptic col-
oration of sandhill cranes makes them difficult to observe during aerial sur-
veys, their nests are usually large and conspicuous from the air (Bishop and
Collopy 1987, Bishop 1988, Bishop et al. 1991). Aerial surveys are normally
conducted during the breeding season (January-June). Nesting activity is best
determined based on several surveys spaced several weeks apart throughout the
breeding season. However, if only a single or a limited number of surveys is
feasible, then it is recommended that surveys be performed later in the breed-
ing season. Either a fixed-wing aircraft or helicopter may be used to conduct
aerial surveys of a site. Fixed-wing airplanes have been successfully used for
sandhill crane surveys when flown at an altitude of 165-500 ft (50-150 m) with
a flight speed of approximately 90 mph (145 km/hr) (Dwyer 1990, Bishop et
al. 1991). Helicopter surveys should be flown at an altitude of 115-300 ft (35-
90 m) (Bennett 1989b, Dwyer 1990). It is best to conduct aerial surveys on
calm, clear days, when visibility will be best. Although aerial surveys may be
the most effective method, they are often too costly to be used in many man-
agement situations.

In addition to surveys, a thorough search for documented historical
sandhill crane nesting activity on an area and adjacent property can be con-
ducted to determine possible past use of the area by sandhill cranes. Both the
Florida Game and Fresh Water Fish Commission and the Florida Natural Areas





NONGAME WILDLIFE PROGRAM TECHNICAL REPORT


Inventory maintain databases of recorded locations of wildlife species. In
addition, local chapters of the Audubon Society may be able to provide infor-
mation about a specific area. If sandhill cranes used an area for nesting during
past years, that area may contain potential nesting habitat, often depending on
current water levels and recent rainfall patterns. It is also possible that appro-
priate management on such an area could return overgrown or degraded areas
to suitable nesting habitat.


MANAGEMENT CONSIDERATIONS

Wetland Habitats

A management plan for sandhill cranes should include some provi-
sions for maintenance of suitable wetland habitat. The pickerelweed/maiden-
cane wetlands that are important crane habitat may become unsuitable for
sandhill crane use without appropriate management. If possible, the wetland
habitat should be maintained as a herbaceous natural system. It may be impor-
tant to maintain the quality and quantity of incoming or outgoing water to
avoid succession to a cattail/willow (Typha spp./Salix spp.) community or a
community of other woody plants. If an area managed for sandhill cranes
becomes degraded in this manner, cattail control or water level manipulation
could be used to restore the area to suitable sandhill crane habitat.

Precautions should be taken to ensure that hydrology is not altered due
to the placement of impermeable surfaces (e.g., roads) adjacent to the managed
wetland. Ponds (e.g., livestock pond) that are created in areas used by sandhill
cranes can be constructed in such a way as to provide additional nesting, for-
aging, and roosting habitat for cranes. A shallow end or shelf that is created
and vegetated with native wetland species will provide a potential nesting site
for cranes. To be suitable for sandhill crane use, wetland areas are typically
composed of relatively shallow areas, with normal water depths ranging from
0 to 31.5 inches (0 to 80 cm). For this to be successful, livestock will need to
be kept off of that portion of the pond. Livestock use tends to reduce the
amount of vegetation within and at the edge of wetlands and ponds.

Upland Habitats

Management for maintaining or creating suitable sandhill crane forag-
ing habitat should include activities that would keep the area in herbaceous
vegetation. Sandhill cranes prefer foraging in vegetation, particularly grasses,
less than 20 inches (0.5 m) in height. Several possible management options
include burning, mowing, or grazing. Frequency of burning would depend on






ECOLOGY OF THE FLORIDA SANDHILL CRANE -STYS


the type and density of vegetation on a site. Time of year should be considered
when planning a controlled burn. It is best to conduct burning or mowing out-
side of the nesting season and after young are capable of sustained flight.
Grazing can be an appropriate management tool as long as an area is not over-
grazed. Generally, grazing at rates or densities recommended for livestock pro-
duction and pasture health appears to provide satisfactory crane habitat.
Agricultural extension agents may be consulted for information regarding
appropriate livestock stocking rates based on the area and vegetation types pre-
sent. The Natural Resources Conservation Service may be contacted for infor-
mation on restoration of native grassland.

Sandhill crane management is compatible with many agricultural uses
of land. However, there are a few adjustments that may make an area more
suitable and less hazardous for cranes. If fencing is used in an area that is to
be also managed for cranes, a three-strand fence with the bottom strand 18
inches (46 cm) from the ground is easier for cranes to crouch down and walk
under and is thus less dangerous than a four- or five-strand fence (Nesbitt
1996). Additionally, a framed walk-through (24 inches high x 18 inches wide)
placed periodically (every 0.3 miles) in a woven wire fence would allow cranes
to walk through the fence but still restrain livestock (Nesbitt 1996).

Response to Disturbance Nesting Season

Management plans for sandhill cranes subject to disturbance during
the breeding season should include provisions for nest site protection buffers.
Buffers should be designed to keep disturbance activities at a sufficient dis-
tance to prevent crane nesting from being interrupted. A buffer zone extend-
ing approximately 400 ft (125 m) from the nest would include reported flush-
ing distances (250 ft, 75 m) and also allow for an awareness zone (150 ft, 50
m). Cranes may be aware of a disturbance factor without necessarily respond-
ing in an obvious manner, such as flushing, as long as the disturbance factor
remains within the awareness zone. Disturbances within the awareness zone
can interrupt the nesting pair and may even cause abandonment of the area.
The size and configuration of a nest site buffer will depend on site conditions
and the individual pair of cranes. Observations of crane responses can be used
to modify the boundaries to protect the nesting pair while reducing the impact
on desired human activities.

Cranes and People

If providing for the needs of sandhill cranes within a semi-developed
area is a goal of a landowner or land manager, some time should be spent
reviewing management practices that would be beneficial to sandhill cranes.






16 NONGAME WILDLIFE PROGRAM TECHNICAL REPORT




Land use practices that directly or indirectly cause sickness, reduced reproduc-
tive ability, reduced prey availability, or death (e.g., pesticide use) should be
avoided in areas managed or set aside for sandhill cranes.

When cranes are in close proximity to people, there are some precau-
tions that should be taken. Potential crane-human conflicts may be avoided if
people remember to treat sandhill cranes as wild animals and maintain a safe
distance. Many rural and suburban residents regularly offer food to local sand-
hill cranes. Cranes may appear to become tame, even eating out of peoples'
hands; however, 'tame' sandhill cranes can quickly and easily become a nui-
sance. During the breeding and nesting season they can become territorial and
quite aggressive, considering people and pets as potential adversaries.
Reflective surfaces and windows that cranes can easily approach can result in
the crane reacting aggressively (S. A. Nesbitt, personal communication).
Caution should be used when cranes are in close proximity to reflective sur-
faces, especially during the breeding season. Planting a visual buffer in front
of the reflective surface or fencing the area off may eliminate or reduce this
problem.






ECOLOGY OF THE FLORIDA SANDHILL CRANE STYS


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