BEHAVIORAL ECOLOGY OF YOUNG AMERICAN ALLIGATORS
DAVID CHARLES DEITZ
A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF
THE UNIVERSITY OF FLORIDA
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
It is a pleasure to acknowledge my committee chairman, A. F. Carr,
Jr., and my supervisory committee, W. Auffenberg, J. H. Kaufmann and
D. A. Dewsbury, for their advice, encouragement and patience from the
beginning of this study. Special thanks are due to Tommr Hines for
his constant support, criticism and invaluable companionship in the field.
H. W. Campbell has also contributed many worthwhile ideas and criticisms
throughout the study, for which I am most grateful.
Financial support was provided by a grant from the Division of
Sponsored Researcn of the University of Florida to A. Auffenberg;
technical and logistical help as well as additional financial support
was dcrated by the Florida Game and Fresh Water Fish Commission. The
Florida Department of Natural Resources permitted access to Payne's
Prairie State Preserve, and A. F. Carr, Jr., allowed me to work on his
property. Those who provided field assistance are too numerous to
thank individually, but I owe special appreciation for the efforts oD
R. Ashton, S. Ganci, T. Goodwin, D. Jackson, K. Prestwich, C. A. Ross,
M. Salzburg, D. Simmons, and A. Woodward. P. Murphy generously made
her equipment at the .Savannah River Ecolcgy Laboratory available, and
assisted with my experiments there.
Discussions with T. Joanen, L. McNease and T. Hurphv at the
inception of the study were extremely helofui, and regular exchange
of ideas with H. Hunt, J. and M. Kushlan, and C. A. Ross was stimu-
iat:ng throughout. L. ?. Franz, J. and M. Kushian ana 2. Rodda allowed
me to use their unpublished data. M. Conlon assisted with the data
analysis and E. Belcher prepared the figures. Finally, I thank D.
Gillis for her expert typing and editorial advice, and my wife, Joan
Spiegel, for encouragement and assistance with the manuscript.
TABLE OF CONTENTS
ACKNOWLEDGEMENTS . . .
ABSTRACT . . . .
I INTRODUCTION . . .
II STUDY AREAS . . .
Orange and Lochloosa Lakes. .
Payne's Prairie .
Lake Griffin. . .
Station Pond .
III GROWTH, MORTALITY AND MOVEMENTS OF JUVENILE ALLIGATORS.
Methods . .
Results . .
Discussion. . .
!V SOCIAL BEHAVIOR OF JUVENILE ALLIGATORS ..
introduction . .
Methods . . .
Resu lts . . .
Discussion. . . .
V EXPERIMENTAL ANALYSIS OF THE VOCALIZATIONS OF
JUVENILE ALLIGATORS . .
r.troduction . .. ..
Methods . . .
Discussion. . . .
VI SUMMARY AND CONCLUSIONS . .
LITERATURE CITED. . . .
IOGTRATPHICAL SKECH . ...
i I i I
i i i I I
I I I ( I
Abstract of Dissertation Presented to the Graduate Council
of the University of Florida in Partial Fulfillment of the Requirements
for the Degree of Doctor of Philosoohy
BEHAVIORAL ECOLOGY OF YOUNG AMERICAN ALLIGATORS
David Charles Deitz
Chairman: Archie Carr
Major Department: Zoology
The behavior and ecology of young A.ligator miss..sippirenis were
studied at several north and central Florida Iccalities. Growth and
movement rates were calculated from recaptures of tagged alligators.
Growth rates varied significantly with haoitat, ard were intermediate
between rates reported for south Florida and South Carolina alligators.
There were no significant differences between growth of male ana 'emale
Survivorship of alligators through their first post-hatching year
was .30 for juveniles from lake habitats and .17 for shallow marsh
juveniles. Two-year survivorship was .14 for a sma,! sample of fake
animals. Injuries were significantly more frequent in shallow marsh
than in laKe juveniles, suggesting that increased predation on alligators
in marsh hac'tats w.as responsible ,for the higher mortalities there.
Pods (sibling grous of hatch ing a!ligatcrs) remained esr r'.e
nes: for a mean of days after hatching. Most pods at this time were
found ;7n Lte guard pc:'-: created a"nd used by the adult female alligator
during incubat on. Movement of pods from the nest to the mother's den
where they overwintered included stops at small pools which were
apparently created by the parent. Pod dispersal began in June of the
year following hatching, but after one year most juveniles were still
within 200 m of the den. One to two-year old alligators continued to
disperse, and it appeared that most two-year-olds had lost all contact
with their natal areas. Rates of movement of juveniles greater than 31
cm snout-vent length also varied with locality, and were identical for
males and females.
Hatchling alligators emerged synchronously to bask each morning
about one hour after sunrise. Emergence was accompanied by a marked
increase in vocalization, and resulted in an extremely close aggregation
of all ood members (social bask). After the morning bask hatcnlings
spent the remainder of the day in the water, largely inactive. At
sunset, pods again began to vocalize rapidly as individuals emerged
from cover and dispersed to forage. Average rates of vocalization for
the first hour after sunset were significantly higher than rates observed
during the day. Shortly before sunrise most individuals returned to the
vicinity of their initial emergence point; final reaggregation of pods
took place during the social bask.
Juveniles emitted the juvenile grunt vocalization in most contexts
involving movement by juveniles or by the parent. Grunts were used as
homing signals by juveniles when separated from the pod. The hi;n-inten-
sity grunt, or juvenile distress call, emitted in distress contexts was
not clearly distinct from grunts used in other contexts.
Parental care inviolvng reculr maternal attendance or defense was
observed for 314 of a~l pods. 'uration of care ,as vKrlable: one pod
was defended through June. A history of human disturbance at some
localities was associated with low observed frequencies of pod attendance
and defense. Adult females threatened intruders with a series of threat
displays also employed in other intra- and interspecific agonistic
encounters. Vocalizations of juveniles were important in provoking
defensive behavior by adults.
Playbacks of recorded juvenile grunts attracted adult and subadult
alligators of both sexes. Adult females responded to playbacks more
rapidly and employed the inflated posture more often than adult males.
Hatchlings presented to two females during olaybacks were taken into
the mouth and released unharmed. Juvenile alligators in the field were
initially attracted to playbacks of juvenile grunts, but sought cover
if playbacks were continued. In artificial enclosures, juveniles were
consistently attracted to such playbacks. These experiments suggested
that the juvenile grunt functions to alert other juveniles and adults
to novel stimuli without conveying any information oi their nature.
Few extant reptiles command the awe that has been accorded to
crocodilians. Human fascination with crocodilians is long-standing;
crocodilians are prominent in the mythology of many tropical cultures.
As others have noted, the writings of many early New World naturalists
reflect little reluctance to borrowing from this mythology when describ-
ing crocodilian life histories. While this has made for some fascinating
reading, it has left the credibility of many authors to question. Con-
tradictory descriptions of the behavior and ecology of many species of
crocodilians abound, and it has become common for crocodilian natural
history accounts to begin with a discussion of how crocodiles do not
behave (e.g., Mcilhenny, 1935; Neill, 1971). Scientific evidence
sufficient to resolve some of these controversies has accumulated oily
within the last fifteen years. Many workers familiar with the behavior
of other reptiles have found early descriptions of courtship display or
parental care i: crocodilians impossible to accept (e.. LeBuf 4 1957).
Some of this skepticism is understandable i, light of tne other incredible
tales associated with crocccilians. Certain' ?Poley's (1977) photo-
graphs ard accounts of care.trai care in Ctocedy.-, 3'7.ictous are no
less remarkable than Topse! s discourse on tne Croccdy.ie of the N*lius
The confusion r.g araino man/y pub ished accounts o0 croociian
natural history is augmen:ed by the Oehav;or of the subjects themselves.
Crocodilians are nocturnal, and even by day secretive and difficult to
observe. Many species occupy densely vegetated or remote areas. In
addition, they are behaviorally very sophisticated reptiles. Recent
work has demonstrated that crocodilians possess well-developed sensory
abilities (Bellairs, 1971), display repertoires and social systems
(Modha, 1967; Garrick and Lang, 1977; Garrick et at., 1978), learning
abilities (Northcutt and Heath, 1971) and reproductive behaviors which
include extensive parental care (Hunt, 1975; Pooley, 1977).
Most of the generalities about crocodilians can be applied to the
American alligator, AZZigator mississ'ippianss. Neill (1971) has reviewed
much of the 18th and 19th century alligator lore, and discusses the
practice of applying Old World crocodile fables to American alligators.
Neil decries those writers whom he believes to have been most guilty
of legend-mongering or an unscientific approach. Unfortunately, Neili
himself falls into this category at times, and his bock inadvertently
serves as an example of the phenomenon it seeks to end !see reviews of
Neill, 1971, by Fogarty, 1972, and King, 1972).
More accurate life nistories (in general) of the American alligator
were provided by Reese (i9i5) and Mcilhenny (1935). 3oth of these
were largely narrative and the data presented were of limited value.
Renewed conservation interest in the alligactr beginning in the
1960's has led to some preliminary qjantitative studies on growth (Hines
et at., 1968), feeding (Fogarty and Albury, 1967; Chabreck, i371;
Valentine et al., 1972), movements (Cnabreck, 1965; Joanen and McNease,
1!70, 1972a: McNease and Joanen, 1974) and pcpulation dynamics
(Chabreck, 1966; Joanen and McNease. 1972b). The severely declining
status of many alligator populations at this time has also made new
information on reproductive ecology and behavior vitally important;
in this area especially the speculations and anecdotes of earlier
workers have been supplemented with more extensive data from recent
The reproductive cycle of AZZigator mississippiensis begins in
March, when an increase in bellowing and courtship display by adult
males and females is observed (Joanen and McNease, 1975; Garrick et at.,
1978). Increased movements by adults of both sexes, presumably related
to mating activities, are also observed from March through late May
(Joanen and McNease, 1970, 1972a; Goodwin, 1977). Most actual mating
in the wild in Florida probably occurs in May (Garrick et al., 1978;
pers. observations). Nest construction in north Florida normally
begins in mid-June, possibly depending on air or water temperatures;
the amount of time spent in nest construction may e somewhat longer
in Florida than in Louisiana, but eggs are apparently laid at about
the same time (Joanen, 1969; Deitz and Hines, in press).
There has probably been more controversy surrounding the sub-
sequent reproductive behaviors and parental care by female Alli-ator
nmiissi'pie-;sis than any other aspect of alligator natural history;
the confusion in the literature is certainly long-standing. William
Bartram's description of alligator habits In 1791 includes the state-
ment: ;. .certain it is, that the young are not left to shift
for themselves; for I have had frequent opportunities of seerig he
female aIligator leading about the shores her train of young ones,
just as a nen does her brood of cnickens; and she is ecualiy assiduous
and courageous in defending the young... ." (Bartram, 1791, p. 122).
Unfortunately, many of Bartram's other statements about alligators are
exaggerated or erroneous. Parental care after hatching was also referred
to by Audubon in 1827 and by some of his contemporaries (see Neill,
1971). But beyond these narratives, few scientific investigations of
alligators have reported any after-hatching care. Reese (1915) stated
that the female alligator liberated the young from the nest in response
to their vocalizations, but did not discuss their fate after this.
Kellogg's (1929) review concludes that it is "generally accepted that the
adults do not show any special consideration for the young after they
are hatched," but also allows (with reference to Bartram) that "such may
not always be the case" (Kellogg, 1929, p. 13).
Mcllnenny's (1935) book on alligator natural history described
parental behaviors previously unreported for any crocodilian, or in fact
any reptile. Alligator nest-guarding and nest opening behaviors were
discussed, and Mcllhenny became the first to describe: 1) the movement
of young from the nest to the den site, led by the female; 2) tre
persistence of the aggregation of young alligators, hereafter referred
to as a pod, into the following spring; 3) defense of the pod by the
female through the following spring; 4) growth and 'ood habits of young
alligators; and 5) the eventual dispersal and maturation of juveniles.
As Carr (1976) pointed out, most of Mcllhenny's ocservations were
subsequently proven accurate. His account was, iike its predecessors,
primarily narrative, and until recently there were few quantitative
data available on alligator behavior.
Chabreck (1965) provided additional reports of the movement of
young alligators from nest to Jen, and followed Mcl-henny in implying
that there was a limited amount of protection by the parent. Both
Chabreck (1965) and Mclihenny (1935) worked with Louisiana coastal
marsh alligators, and indicated that in this habitat pod dispersal began
in spring. Fogarty (1974) reported that young alligators in the
Florida Everglades may remain near the female's den for two or three
years after hatching, but denied the existence of any active protection
by the parent. Several large scale studies of alligator nesting ecology,
covering most of the animal's present range, were recently completed;
all of these reported a variable degree of nest attendance by the female
and in most instances opening of the nest by her in order to liberate
the young (Joanen, 1969; Fogarty, 1974; Metzen, 1977; Deitz and Hines.
in press). Of all the accounts since Mcilhenny only one, based on a
single observation, provided any further direct evidence for parental
care of the young after hatching (Kushlan, 1973).
At the inception of this study most other aspects of juvenile
alligator behavior and ecology remained equally obscure. Despite the
wide variety of wetlands habitats occupied by alligators, information
on growth and movements was available only for the Louisiana coastal
marshes and, to some extent, for the Everglades; no data were avail-
able on the influence of habitat on life history parameters. Obser-
vations suggesting that the vocalizations of young alligators were the
principle mechanism by which pod cohesion was maintained were mace oy
Campbell (1973) and Herzog (197'-'), but no experiments had been performed
to test this hypothesis.
The variety of habitats occup~ec Dy 'i.gaTvor mississippiensia
in north ard central Florida provided an opportunity to examine
juvenile behavior in different ecological contexts. I began this
investigation to: 1) obtain information on the growth, mortality, move-
ments and dispersal of juvenile alligators in Florida; 2) determine the
extent and persistence of parental care; 3) examine communication and
social behavior within the pod through field observations and experi-
ments; and 4) determine the influence of habitat on the above by studying
juveniles in different locales. Several excellent accounts of social
behavior and parental care in other species of crocodilians appeared
during the study (e.g., Garrick and Lang, 1977; Pooley, 1977). Conse-
quently, it also became possible to make some preliminary comparisons
between Alligator mississippiensis and other crocodilians with respect
to the ecological and evolutionary significance of parental care and
juvenile social groups.
Orange and Lochloosa Lakes
Orange and Lochloosa Lakes (Alachua County) form a twin-lake
system connected by Cross Creek, which runs from southwest Lochloosa
Lake to northeast Orange Lake (Fig. 2-1). Botn are large mesotrophic
lakes, with extensive marshy areas covering portions of the basin
(Brezonik and Shannon, 1971; Table 2-1). Mcst observations of juveniles
were in these marshy areas, although several groups of juveniles were
located along the marshy fringe around the open water portions of the
lakes. Characteristic of marsh areas of these lakes is a heavy build-
up of peat. Gasses formed by deccmpos;tion bring large chunks of peat
to the surface, resulting in floating islands and floating mats exteno-
ing out from the lake shore. Vegetational composition of these islands
and f ngee a-eas is largely Sagittjia yancif"i, Cfi n j'icerensis,
c-.aoidenta-'is and Deco'cr. ertici.lc..s. B. car erni covers extensive
portions of the open water margins, with i:snornic c assipes, 7i"obi m
spc' and oi.t.l fra.'t-es comtmor in more sheitereJ areas. There ,2
aburdart su-mnerged growth of .Ydi'lZt verc'-iL''aZa.
Seasonal variation in water tmpe-a'. -: a Ornc. Lake is shown
.n Fig. 2-2. P"dctably, shalow water aas in t~e la e frince and
marsh regions showed g.earr d;el fluctuation, heating up rapidy, in
Table 2-1. Study areas.
1. Orange Lake
2. Lochloosa Lake
3. Lake Griffin
4. Station Pond
5. Payne's Prairie
6. Lake Wauberg
7. Biven's Arm
8. Carr property
Trophic State Index
Values for mean depth and trophic state index are from Brezonk and
Shannon (1971) except values from Payne's Prairie which are from
Surface areas taken from U.S. Geological Survey data, or calculated
from aerial photographs via planimetry.
Florida. Uurbers correspond to Taole 2-i. Dashed
< --- ---.10---m
^^/ \ LAKE
Figure 2-1. Locations cf principal study ares in north and central
Florida. Numbers correspond to Taole 2-i. Dashed
portions of areas 1 and 2 indicate the marsh areas of
Orange and Lochloosa Lakes.
(0o) in 3din 0 nZH
r ) 0C.
(00) 3fni'dct3dV31 OZH
the sun and cooling below average lake temperature at night. Water
levels fell gradually throughout the study period until 1977, when
abnormally low rainfall resulted in a 20-year low in the lake level
(Fig. 2-3b). This produced exposed mudbanks around lake shores and
an extension of the fringe vegetation into the center of the lake. The
Orange Lake alligator population at the height of the drought was
estimated at over 2500 individuals based on night census data (Hines,
Payne's Prairie (Aiachua County) is a large solution prairie
typical of Florida wet prairie habitat, except that drainage canals
ana levees have been constructed throughout for flood control. it is
now a portion of Payne's Prairie State Preserve. White (1974) has
presented data on hydrology, vegetation and dynamics o" plant succession
on Payne's Prairie. Alligators are commonly fcurd only in the wetter
portions of the basin. Dcrminant p!-ant species in these areas include
PcintdericE ocrdlatai, Jusazasc peru^sv^ianjr*, T CZha so., SaiZC carolinmnsis,
Panc-i- 'remasr:, Jurcs 2f'fusu, lt"ibc n.r. .c and Hyccctjye
,nce ~ata (Wh':e. 1974). after r levels during the study period are
presented in Fig. 2-3a; drainage of Payne's Prairie has been artificially
contrlied since rnid-1976. Water temperatures show daily fluctuations,
in keeping with the shallow decth hrouchout most of the marsh. Season
temperature chances are presented in Fig. 2-2.
Aeria; nest surveys in 1576-1977 and casual observations at night
indicatedd that Payne's Prairie probate iy supports a,, a!iigator popular ion
comparable to Orange Lake in cenosn.y. but no censuses ,.ere conducted.
IFMIM r A A ON'D F M AM'J J Al S 1ND JF MAM J JA N
'MJJ .AE % ~ j! I J I ~
...'%.. / r
UnAIU~t LAt- ---
j 'F M' M'JJA'SON DIJ'F MAM J A SON D JFMAM' iJ IASON',
1975 1976 1977
Water levels at three study sites, 1975-1977: Payne's
7rairie, top; Orange Lake and Lake Griffin, bottom.
Lake Griffin (Lake County) is the last lake in the Oklawaha Basin
chain of lakes; it drains directly into the Oklawaha River. All
observations in this study were conducted in Picciola Cove, in the south-
western portion of the lake. As in Orange Lake, peace build-up has
produced a floating mat around the fringe of the lake; in Lake Griffin
this forms a dense thicket rather than a floating marsh, composed
principally of woody plants such as Acer rubr'mn, Cephlanth.us ocietais,
Salix carolin-ensis, and Nyssa sylvatica. There are emergent growths
of Sagittaria sp., Nuphar lutem and Panicuan repens. Alligators of all
sizes used trails and holes in this fringe.
Lake Griffin was characterized by Brezonik and Shannon (1971) as
hypereutrophic (Table 2-1). The development of this condition was due
in part to high volumes of citrus cannery and municipal sewage effluent,
and also to artificial stabilization of water levels. Water levei
fluctuations were minimai during the study (Fig. 2-3b). Water tempera-
tures (Fig. 2-2) averaged higher than in Orange Lake, probably as a
result of its more southerly location and greater depth (F:g. 2-1;
Alligator reproduction on Lake Griffin has been explosive in recent
years. This has produced populations which are extremely dense and
composed largely of juveniles less than i50 cm in total length (Hines
unpub. data; pers. observations).
Station Pond (Levy County) is the only study area located in the
Gulf Coast drainage (Fig. 2-1); it forms part of the headwaters of the
Waccasassa River. It is a shallow, sand-bottomed basin, surrounded
mostly by pine flatwoods except at the southwestern end where it grades
into cypress swamp. Principal emergent plant species in the marsh were
Panicum hemnatomon, Nymphaea odorata, Brasenia schreberi, and Ponvederia
cordata. Slightly higher islands in the marsh, referred to as "heads,"
were often associated with alligator holes. Vegetation on these heads
was predominantly Panic wn hematomon, Cephalanthus occidntatis,
Sagittarea Zancifolia, and a variety of undetermined species of ferns
and herbs; some heads also included one or two cypress trees, iaxodium
No monthly water level or temperature data are available for
Station Pond; temperature data available for Payne's Prairie (Fig. 2-2)
are probably a reasonable approximation. Tne water level of Station
Pond appears dependent on regular rainfall, for during periods of low
rainfall it would drop markedly. Station Pond became completely dry in
May 1977, and except for a brief reflooding after rains in September,
remained dry until January 1978. During this drought, the only
surface water available was in alligator holes--depressions which are
deepened and kapt clear of emergent vegetation by the activity of the
resident alligator (see Mcllhenny, 1935,and Craighead, 1968). Prior
to 1977 the all;5ator population on Station Pond was estimated at
5C-120 individuals (Hines, Woodward and Deitz, unpuo. data).
Brazonik and Shannon (1971) have presented productivity and water
chemistry data for Watermelon Pond, a marsh which is slightly deeper
but otherwise very similar in appearance to Station Pond. Watermelon
Pond is also in the Waccasassa drainage and is located 2.2 km to the
northeast of Station Pond. The trophic state index for Watermelon Pond
has been used for Station Pond (Table 2-1).
Occasional data were also obtained on alligators in three other
locations, all in Alachua County: Biven's Arm and Lake Wauberg, both
part of the Payne's Prairie drainage system, and a small pond on the
property of A. F. Carr, Jr., near Micanopy, Florida (Fig. 2-1).
Significant features of these study areas are discussed with results
GROWTH, MORTALITY AND MOVEMENTS OF JUVENILE ALLIGATORS
Quantitative ecolog ca.l studies of crQcodil ians have been few, and
with the exception of Cott's (1961) work with Crocodylus niZoticus have
been restricted to populations occupying single habitat types. Most
data on growth and mortality in Alligcat-or ;n'ssissippiznsiis have come
from the Louisiana coastal marshes, where salinity Is the only major
environmental variable affecting populations in different marsh areas
(Joanen and McNease, 1972b; Chabreck, 1965, 1971). Growth rates of
Louisiana and south Florida juvenile alligators are comparable (Mc Ihenr.y,
1935: Hines zv at., 1968) and are both much higher than rates reported
for South Carolina (Bara, 1972; Murphy, 1976), suggesting tnat length
of the active season is important. Data on natural mortality of A.
micsiissppiensis (or of most other species) are non-existent, except
for indirect conclusions based on life tables (Nichols et al., 1976).
Chabreck (1965) described the oost-hattci-.ng movements of .4.
m'issis-L.p.'.ie'sz in Louisiana, and indicate that they were influenced
by vater levels. Similar results were reported from T-he Everglades
(Fogarty. 1974), and formation of pods was apparently typical after
matchingg in bctr areas. The durat'on of these pods, distance moved and
extent oF interaction with the parent w.vere rot clearly defined. Neil 's
(1971) assertiorns that Florida juveniles did not form groups were
entirely urfo-unded, but the extent to which lake habitats in north
and central Florida might cause divergence from marsh movement patterns
was unknown. The implications of Chabreck (1965) and Fogarty (1974)
that pod formation, dispersal and possibly duration of parental care
were affected by water levels and other habitat characteristics indicated
that information on the natural history of Florida juvenile alligators
was basic to any understanding of the significance of social behavior
and parental care.
Alligator nests were located on Orange and Lochloosa Lakes and
Station Pond using aircraft, and on Payne's Prairie by searching levees
on foot. Brushy cover in the fringe areas of Lake Griffin made both
air and ground searches for nests there impractical, and only two were
located. Nests were usually checked semi-weekly and observations on
female behavior were made at this time. Observations of one nesting
female were also made at the Carr property. After hatching, pods were
followed on foot or by canoe on Payne's Prairie and at Carr's, and by
boat on Orange Lake and Lake Griffin.
Most alligators were captured at night--those under 155 cm in
total length by hand or with tongs. Snout-vent length (SVL, taken from
the tip of the snout to the posterior angle cf the vent), total length
(TL), and weight were normally recorded for all alligators captured.
Evidence of injuries was also recorded. Loss of the tail rip, i.e.,
the distal 20% of the tail, was considered to be a minimal disfigurement;
loss of a l;mb or a substantial portion of the tail and signiF cant
scars or wounds on the head or trunk were considered to be severe
injuries. Sex was determined by cloacal examination for specimens
with a TL of 45 cm or greater (Chabreck, 1963). Locations of all
captures and recaptures were plotted to the nearest 100 m using aerial
photographs; even more precise locations were usually possible with this
method. Alligators were marked with monel tags (National Band and Tag
Co., Newport, Ky.) inserted through the webbing between the second and
third toes of the right hind foot and released.
When working with pods of hatchlings, an effort was made to
capture all individuals sighted. I assumed that this resulted in a
relatively equal capture effort for successive captures and used the
Lincoln Index to estimate the number of hatchlings in a pod. Alligators
of all ages became extremely wary when recapture attempts were frequent;
therefore, the interval between successive captures of the same pod
was usually 3 months. Since pods were usually eeli separated, locations
of different pods could be determined without confusion by visual
sightings. Survivorship was calculated by two methods: 1) hatchlings
tagged at the initial encounter witn a pod were taken as a representative
sample, and subsequent recaptures cf these initially tagged individuals
on1y were user to determine survivorship; 2) estimates of the number of
hatchlings present on- a given date were made on the basis of either tne
Lincoln Index or visual census, whichever was greater.
The movements of alllgatcrs on Orange Lake and Payne's Prairie
were tracked by radio celemecry. Transmitters of i50-151 MHz with short
whip antennae were -3ei. 3at'ery sizes and conf;grat ions of the
packages /ariec, btt none of the packages exceeded 5% of the body weight
of the alligator instrumented. Two attachment methods were used: 1)
steel wires molded into a water-proof instrument package were passed
through holes drilled transversely through the nuchal scutes of the
alligator; or, 2) straps of nylon elastic and surgical tubing were
passed around the body anterior and posterior to the forelimbs.
Longitudinal strips dorsal to the forelimbs prevented the transmitter
from sliding ventrally. Instrumented alligators were located at least
once every 72 hours.
All analyses of growth and movement data were done by computer
using standard SAS76 statistical packages (Barr et al., 1976). Growth
races were expressed as increment in snout-vent length (SVL) in cm per
month or in weight in gm per month, calculated by the following formula:
SVL2 (or Weight 2) SVL1 (or Weight 1)
Days from capture i to capture 2
Movement rates were calculated in a similar fashion by substituting
distance moved between captures for growth increment.
In order to examine the effects of increasing body size on growth
rate, alligators were divided into 3 size classes: class I, < 20 cm SVL;
class li, 2i-31 cm SVL and class III, > 31 cm SVL. The rationale for
these divisions was that they appeared to correspond to alligators irom
hatching t:hrourg the beginning of activity the next spring (SVL c'ass i)
juveniles from aocut 0.5 to 1.5 years old (yearlings, SVL class I!) and
larger juveniles (SVL class ll ), 1.5 years old or older wnich had begun
significant dispersals (see beicw). Some variation in crcwth rate
produced by size was also reduced by expressing growth rates as percent
change in initial SVL (or weight) per month.
Observations of winter dormancy in north Florida alligators
indicated that little growth probably occurred during this period;
food consumption was much lower than during other periods (Deitz and
Hines, unpublished data). Recapture intervals of juvenile alligators
from different locales varied considerably, and included different
proportions of winter days. For example, an alligator captured on 1 May
and recaptured on 1 October of the same year had the same recapture
interval (5 months) as an animal captured on 1 November and recaptured
on 1 April of the next year. Growth incrementss of these two alligators
were likely to be quite different. In order to eliminate this variable
when comparing growth rates between locales, the days from 1 April
through 31 October were considered to be "growth days," while days from
I November through 31 March (151 days) vere considered tW be "no-growth
days" and were not counted in the recapture interval. Monthly rates
calculated in this manner and then multiplied by 7 compared favorably
with annual growth rates calculated for long-term recaptures.
Growth rates of juvenile Aligatcr mississippinsis from different
localities varied considerably (Table 3-'). As expected, the rates
decreased at all locales as oody size increased. At all sizes, alligator-
from Orange Lake grew Faster in length and in weight than animals frcm
01% co U
C14 N -N
cn CS4 -T
-ro o L.r co
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.14 C, 4
- 0 0-
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oo a -^ C
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other sites, while growth of alligators !n Lake Griffin was generally
less when compared to all other locales. Growth rates for Station Pond
and Orange Lake were comparable except for size class III; Station Pond
data were based on captures of more large juveniles (SVL 50-70 cm) than
any other areas, which probably biased these rates downward. Growth
rates at Lake Wauberg were generally low, although samples were too
small for valid comparisons. Differences in water temperatures (Fig.
2-2) and water depth (Table 2-1) which might affect the length cf the
active season and/or food abundance, did not satisfactorily explain
differences in growth rates. Stomach contents of juveniles from Orange
Lake and Lake Griffin suggested that in Lake Griffin low availability of
aquatic invertebrate prey was limiting to alligator growth (Deitz and
Hines, unpublished data).
Data from two 1975 cohorts which were regularly recaptured on
Orange Lake (Fig. 3-1) and Lake Griffin (Fig. 3-2) show the actual
growth of juveniles for two years after hatching. These and other
data from long-term individual recaptures compared favorably with the
mean rates calculated from all recaptures within a locale (Tabie 3-1).
Recaptures from October through April supported the assumption that
there was no growth in north Florida juvenile alligators during a
winter dormancy period of roughly five months, from I November to
31 March. This can also be seen in Figs. 3-1 and 3-2.
There were no differences in growth rates between male and female
juveniles when tested either within locales or with pooled data from
several locaces (p > .05, '-tests); thus, data from both sexes were
combined in preparing Table 3-1. The sex ratio for 20 SVL class II
(wuj6) IHO13M 01
l- --i h-^-- i 5
1 I --_ __
0 0 l0
(u3) H19N31 IN3A inONS
(iu5) 1H9i3,, 00o
f t. .
*,^} -'19N31 1N3.A\-ir.ON
alligators was 1.45:1 (males:females); for 443 SVL class III alligators
it was 1.68:1. These ratios were not significantly different (p > .05,
Chi-square test) and the sex ratio for all juveniles combined was 1.59:1,
or 61.3% males and 38.7% females (Table 3-2).
The survivorship of A. mississippiensis frcm hatching through the
end of the first year proved to be surprisingly high for some pods;
both methods of calculation provided similar results (Table 3-3).
Roughly half of all hatchlings from Lake Griffin and Orange Lake
survived the winter, and survivorship after one year averaged approxi-
mately .30 (Table 3-3). Mortality for 3 pods in shallow marsh habitats
(Station Pond and Right Arm Marsh, Lochloosa Lake) was greater, although
differences between lake and marsh survivorship were not statistically
significant. Due to the increased dispersal of two-year old animals and,
in some cases their learned avoidance of capture techniques, few data
were obtained on survivorship from the first through second year. On
Orange Lake, survivorship of two pods from 1975-1977 was at least .14
(10/74) based on estimates, or .19 (6/31) based on animals tagged and
recovered. On Station Pond 4 (.10) of an estimated 41 animals from two
pods were alive after 2 years.
Predation on hatchling alligators was never observed. The wide
range of survivorships of different pods suggested that some groups
were less susceptible than others, but there were no clear differences
in microenvironment. behavior of hatchlings or female attendance (see
Chapter 4) between pods with different mortalities. Estimated survivor-
ship of individual pods over 1 year on Orange Lake ranged from 0 to .49;
1 .0 0
4-J co m
('. Nu-- ~
1.. 0 1U.'
-C 3r -3- c0O 3
D r- -3-
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the range on Lake Griffin was .14 to .56. Temporal patterns of
attrition likewise gave no clues to predator identities. All pods
showed a reduction in mortality with age, which could be due to
increased body size, learning, or both. However, initial mortality
was much higher for some pods than for others at the same site. For
pods in all habitats attrition during the winter was also less than
that observed during the active season. At least 67 of an estimated 88
hatchlings from 5 pods alive in October were alive the next March; this
was equivalent to an annual survivorship of .43.
Indirect estimates of mortality from other locales suggested that
survivorship of individual pods was quite variable there also. One
pod of at least 14 hatchlings had vanished from Lake Wauberg by the
following spring, but nrght counts of 5 other pods in 1977 indicated
that 1 year survivorship on Lake Wauberg was probably as high as that
on Lake Griffin. Survivorship of two pods from different years at the
Carr property were less than .10 and probably 0.
Injuries. The most common injury to small .4. ,i's -ssipz's:s'.
was loss of tne tail tip (Fig. 3-3). Tail tip losses had occurred in
5. i of my entire sanale (n = 1685) and accounted for 58. of all injuries.
Loss of nore than 20% of the tail was recorded in 29 alligators (1.7,),
loss of a linb in 2! (1.3%) and severe scarring on head or trunk in 7
(0.4'). The overall injury frequency increased with size of the
ail igator '(Fi 3-2).
There were substantial differences in the o-rcentage of injuries
between localities. j '-,.enile alligators (SVL < 70 cm) from sha'low
marsh habitats (Station Pond and Payne's Prairie; n = 389) had an
SVLII 20CM SVL 21 31CM
SVL ) 31 CM
Frequency of injuries in alligators from
lake and marsh habitats in north and
D1 TAIL TIP MISSING
- SEVERELY INJURED
injury frequency of 15.4%; this was significantly higher (p < .01,
Chi-square test) than the 6.7% injury frequency for all lake habitats
(Orange Lake, Lake Griffin and Lake Wauberg; n = 1096). Injuries to
marsh alligators were also significantly more likely to be severe than
those of lake animals, and the frequency of these severe injuries
increased with size more rapidly in marsh alligators than in lake
Growth rates (SVL and weight increments) and movements (see below)
of alligators missing only their tail tips were not significantly
different from uninjured alligators (p > .05, t-tests within all locales).
Growth rates for a sample of 11 severely disfigured alligators (SVL >
31 cm) from Station Pond were not significantly different from growth
rates of normal alligators.
Movements and Dispersal
The movements of 17 pods in marsh habitat (Payne's Prairie, Station
Pond and parts of Orange and Lochloosa Lakes) and 6 pods in lake fringe
habitat (Lakes Griffin, Wauberg and Orange) were fo!iowed for at least
two weeks and usually longer after hatching. Observations were also
made on movements of 7 additional marsh and i5 additional lake fringe
pods for in;ch the nest locations were unknown. The initial location
of a pod after hatching was usually a pool or wallow near the nest,
referred to as a "guard pool" by Mcllhenny (1935). Females which defended
their nests were almost invariably present in these guard pools during
incubation (De;tz and Hines, in press), but guard pools were also
present at nests which were not reguiarl, attended. On Payne's Prairie
and Orange Lake, 65 of 93 nests (70%) had guard pools located within 3 m
of the base of the nest. Most other nests had guard pools within 10 m
of the base, connected to the nest site by well-defined trails. Both
the presence of freshly smashed vegetation and the increased depth of
these pools when compared to the surrounding marsh suggested that guard
pools were actively created by the nesting female. Some pools also
appeared to have been enlarged by the female just prior to or shortly
after her nest hatched.
All alligator nests examined on Orange and Lochioosa Lakes and on
Payne's Prairie had a characteristic semicircular excavation after hatch-
ing, and it was concluded that all had been opened by the female (Deitz
and Hines, in press). Hatchlings were probably led or carried to the
guard pool by the female during hatching (Kushlan, 1973; Meyer, 1977)
although hatching was never observed. Hatchlings emerging late and/or
without the assistance of the parent probably had little difficulty
finding the pool because of its proximity, and could also use the
vocalizations of other hatchlings as an aid (see Chapter 5). On one
occasion, two natchiings with umbilices still attached were found
halfway down the trail leading from the nest to the guard pool 5 m
away. The remainder of the pod was in the pool, vocalizing regularly.
The presence 3nd distribution of nest guarding pools, wallows and
other sites associated with adult alligator activity were important in
determining the movements of pods after watching. If a guard pool was
present, hatchlings in a!! habitats typically remained in the vicinity
of the nest for several days. For 9 such rests, hatchlings spent a
minimum of 14.3 + 10.5 days (range 6-39 days) within 10 m of the nest.
Two other nests that were closely observed had no guard pools nearby,
although some water was present at the base of the nest. Hatchlings
from these nests spent respectively, maxima of 5 and 7 days near the
nest before moving away. Three additional marsh nests were located
adjacent to large pools which appeared to be the female's alligator
hole or den site; these pods showed no movement from hatching through
the following spring.
After this variable period near the nest, pods began moving away
to their overwintering site. The integrity of the pod was maintained
throughout these movements, which occurred as regularly-spaced journeys
separated by periods during which pods remained in the same pool or
series of pools (Figs. 3-4 and 3-5). Displacementsof up to 40 m in
24 hrs were recorded; after a long shift in position the pod usually
remained stationary for several days. Females were observed moving
with their pods in two instances, once during the day and once at night.
Parental presence during most other movements was inferred from the
fresh trails that connected new locations with the previous ones. Many
of the small poc!s in which pods were found at this time were clearly
created or enlarged by the movements of the female. Stands of PanCio'n
hematoCon, P'ntederia cordata, Sag.ittaria lancifolia and other soft
marsh plants were found smashed down in roughly circular patterns 3 to
5 m across, which created enclosed pockets in the marsh or lake shore.
The dens of three females which nesced on Station Pond in 1975-1977
were adjacent to heaas or peat islands in the marsh. Trails and pools
wound through all of these heads like shallow canyons; hatcnlings from
two successful nests used these pools for the first t-w months after
/ \.--- .
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1 4 4
4e 4' 4b 4 l
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I 44/ 4 44 4i:' I
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hatching and intermittently thereafter. Observations of young alligators
using heads with similar networks cf pools were made at other shallow
marshes near Station Pond. Two heads with adjacent pools were known
to be used by large males. Neither of these had the extensive network
of small pools observed in heads with young; the large pools adjacent
to the heads were wider, and the alligator trails present seemed to be
straighter. These casual observations suggested that long-term occupancy
of a den by a reproductive female alligator might result in permanent
habitat modifications related to care of pods.
Most pods reached the den or overwintering site by mid-November.
This site appeared to be used extensively by the adult female if it was
not actually her den. Total minimum distances moved for 9 marsh pods
which were tracked from nest to den averaged 80 34 m (range 25-120 m).
The exact route taken was probably more circuitous, as illustrated by
the movements of a pod through shallow marsh at the Carr property ;n
1974 (Fig. 3-5). Though the actual distance from nest to den site was
116 m, the minimum path length for the pod was 445 m, and included two
reversals cf direction and four stops at different sites before the
wintering pool was reached.
Pods on Lake Griffin and on the fringe of Orange Lake snowed a
slightly different movement pattern. After leaving nests on the fringe
of Orange Lake, pods moved gradually out to the edge of open 1w.ater,
and remained there until the onset of cold weather in November: at this
point they roved back tz a den site ii the fringe (Fig. 3-6). Only tvwo
nests were located on Lake Sriffin, out both of thepods from these nests
followed a pattern similar to those on the fringe of Orange LaKe. Each
year in mid- to late September many pods became visible on the fringe
6-15 Oct '76
ADULT 10 Nov'76
.,- 30 Aug-14 Sep'76
Figure 3-6. ovem-ents of the .7609 pod, Oranae Lake.
of Lake Griffin. If peak hatching is assumed to be at about the same
time as on Orange Lake (late August to early September), these pods also
must have spent approximately two weeks near the nest before moving away
and did not follow a direct route from nest to den.
Hatchlings moved little throughout the winter and, as already
noted by Chabreck (1965), were largely inactive except on warm, sunny
days. There was some tendency for pods to be extremely closely
aggregated during cold weather, and their location in extremely small
pockets or pools made them difficult to detect. Two pods observed on
Lake Griffin during the winter of 1976-77 were located several meters
ba< < from the open water margins of the brushy fringe. Both occupied
pools less than 150 cm in diameter. One pod observed on Orange Lake
in March 1977 occupied a pool approximately 2 m across. Water tempera-
tures throughout the winter on both Lake Griffin and Orange Lake ranged
from 15-20'C (Fig. 2-2). Hatchlings were sluggish at these temperatures,
but were capable of coordinated movements and vocalized readily when
captured. When disturbed, they dove underneath the floating mats or
vegetation into underwater refuges, some of which appeared to be caves
used by adult alligators. Some basking took place on Orange Lake
during the winter, and hatchlings on Orange and Griffin also fed,
although at reduced rates, as indicated by stomach contents (keitz
and Hines, unpublished iata). Pods not followed closely during the
winter were found in Ma.ch and April where last seen the previous fal.
Dispersal of alligators following their first winter was documented
by periodic recaptures of pods on Orange Lake, Lake Griffin, and Station
Pond, wi:h sucppementary observations of marked and unmarked juveniles
from these and other locales. The mark-recapture phase of the study,
conducted from 1974-77 in conjunction with the Florida Game and Fresh
Water Fish Commission, resulted in 559 recaptures of 382 alligators, from
a total of 1685 alligators tagged; the majority of these were less than
150 cm in total length.
Representative dispersal patterns of pods of alligators marked on
Orange Lake were plotted in Figs. 3-7, 3-8 and 3-9. All three pods
demonstrated a one-dimensional spreading along the lake or marsh fringe;
dispersal distance after one year was similar for 7 additional pods
studied on Orange Lake. Figures 3-7 and 3-8 also illustrate that the center
of dispersal was the overwintering site rather than the nest. Seven pods
followed on Lake Griffin (Fig. 3-10) showed the same pattern of bi-
directional, linear spreading also observed on Orange Lake. However,
one-year dispersals on Griffin appeared to be slightly less than on
Orange Lake; this was possibly related to slower growth of Lake Griffin
juveniles. As expected, dispersal on Station Pond and in marsh areas
of Orange Lake was more two-dimensional, but the time sequence of
progressively greater displacement from the den site during the first
summer was similar.
Pods were still recognizable as discrete aggregations in Jure of
the first year after hatching in both lake fringe and marsh areas of
Orange Lake, but they began to Jose cohesiveness at aoouc this time.
ReaggrecatIon into a single group following a night's feeding (see
Chaoter 4) no oncee occurred, and several cium:ps of siblings scattered
along 100-300 m of shoreline or in aifferen't pools in the marsh were
-; -' mi rsh ) --
Ot,- _-/-_-". -' =--^S
Figure 3-7. Dispersal of the 2177 pod on Orange LaKe, 1975-1977.
Figure 3-8. Dispersal of the 2301 pod on Orange Lake,
I Sep '77
172 Se7 -$V.--' -
r--"-. _-^ -- -'-,
20 June '77
I I mo, 6
*Z Sep- 14Oc'
Figure ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ EThace 3-P ipes(r)"cMug70fa o rne ae 37-37
One capture from
75 LGI pod
Sep '76 Av
75LGI pod- Sep'76
2533 pod- Sep'77
Dispe5sa3 of 7 marked pods along the
shorei ;ne of Lakz Griffin. 1375-1977.
observed. Prior to the onset of cold weather in late October many
one-year old alligators were solitary, although small groups of siblings
were still regularly found.
Some one-year old animals in all habitats demonstrated movement
back towards their first overwintering site at the beginning of the
second winter. This was evident with pod 2172 on Orange Lake in 1976
(Fig. 3-7). By the end of the summer this pod had dispersed over a
shoreline distance of about 330 m. On 27 October 1976, when water
temperature had dropped to 19.5C, 9 individuals from this pod were
found together within an area of about 25 m A return of 1.5 year old
alligators to their den site was also observed in 1977 on Station Pond,
when severe drought eliminated most of the standing water on the marsh.
Recapture data from hatching through the first year indicated that
there was very little migration of alligators from one pod to another,
even in situations where pods were relatively close together. The 2172
and 2301 pods on Crange Lake both hatched in 1975, and probably were
separated initially by no more than 600 m. Movement early the next scoring
reduced this separation to about 300 m (Figs. 3-7 and 3-8). However,
sibling groups remained distinct until September 1976, when one juvenile
from the 2172 pod was captured with the 2301 pod. In October 1976, two
alligators from the 2301 pod joined the 2172 grouo and overwintered 4itn
them. These 3 individuals represented 8.6A of the estimated 35 ailVgators
surviving from the two pods for at least cne year. No shifts were recorded
in 1976-77 for five pods on Orange Lake. Two t-ans'ocations were recorded
on Lake Griffin in 1975-76, represer:ing a total of 6.1% of the estimated
33 one-year survivors from these 5 pods. On Station Pond, I of an
estimated 8 one-year survivors '12.5 ) was from a different pod; this
one animal appeared only after its siblings had vanished, probably
through predation. Thus, even where nest densities were fairly high,
fidelity to pod or den site was sufficient to support the assumption
that aggregations of one-year-old or younger alligators were composed
almost entirely of siblings. For areas with low nest densities, the
probability that alligators in a group were siblings probably approached
Dispersal of juvenile alligators following the second winter appeared
to be a continuation of patterns of first year dispersal, although fewer
data were obtained in support of this. Larger animals dispersed
farther than yearlings, as shown by plots of two-year dispersal on
Orange Lake and Lake Griffin (Figs. 3-7, 3-8 and 3-10).
Close associations .ith the natal area appeared to oe lost by
about the end of the second year on Orange Lake and on Station Pond,
as indicated by recaptures and visual sightings of known-age and similarly-
sized juveniles. Two-year old alligators remained dispersed at the oegin-
ning of their third winter after hatching. Dispersal on Lake Griffin
appeared to be slower, possibly as a consequence of reduced growth, but
captures and sightings of two-year-olds were few. Two 2-year-old alli-
gators recaptured on Lake Griffin had not moved from their first year
ranges. The brushy shoreline and extreme wariness of juveniles from
Lake Griffin made recaptures infrequent, ard probably biased the sample;
dispersal into fringe areas could have occurred, resulting in low
probability of recaptures or visual sightings.
A summary of movement rates calculated from -ecapture data for the
three size classes of juvenile alligators appears in Table 3-4. For size
mE +1 -' +1 o +1
in "!: o -r c -
0C N 4N c c N C -
0 .1) 0 3
SE- E + + + C
>Cz C cC (
-T N O N
v1 1 -J
classes I and II, only data from Orange Lake and Lake Griffin were
sufficient for a useful comparison. Orange Lake alligators moved
slightly more than Lake Griffin animals; this difference was significant
(p < .05, t-test) for size class I. Larger juveniles from both shallow
marsh habitats (Station Pond and Payne's Prairie) had higher rates of
movement than alligators in the three lake habitats; the difference
between Orange Lake and Station Pond was significant (p < .05, t-test).
Extensive movements (over 1000 m between successive captures) by some
juveniles in size class III from all habitats suggested that movement
rates calculated for this size class were substantial underestimates
The extremely low rate of movement obtained from recaptures on Orange
Lake probably reflects some bias in collecting, since not all areas of
the lake were visited equally. Capture efforts on Station Pond were
more evenly distributed. The longest movement recorded in the study
was for alligator 20103, a male 82 cm in TL at initial capture. This
alligator was captured in the southwest corner of Lochloosa Lake on 7
October 1975, and was recaptured on 17 September 1976 on the east
shore of Orange Lake after moving a minimum distance of 5100 m in
346 days (14.7 m/day).
Movements of males and females were not significantly different
at any of the localities studied. This was not unexpected for alligators
in their first year, since these individuals were still in pods. How-
ever, larger, more solitary juveniles also demonstrated no sex-resatad
differences in rates of movement. In the largestt recapture sample
Zrom Station Pond, -ocvement of males and 4emaies was identical (4.5 +
7.3 m/aay vs. 4.5 + 9.7 m/day for 33 male and 18 female recaptures,
respectively). Data for males and females were combined in the above
comparisons of movement rates between locales.
Alligators tracked by radio telemetry moved very little, with one
significant exception (Table 3-5). However, instrumentation periods
were too short for valid comparisons with mark-recapture data. Movements
of alligator 20337 on Orange Lake (Fig. 3-11) suggested that two year
old alligators may sometimes travel extensively, and that movement
rates calculated from recaptures were low estimates of actual travel.
Number 20337 was probably beginning its third year; the distance it moved
in 20 days exceeded the maximum dispersal through the first 2 years for
all members of the 2172 or 2301 pods on Orange Lake (Figs. 3-7 and 3-8).
Two instrumented alligators were subsequently recaptured after
their transmitters had failed. The sites of both recaptures suggested
that the data obtained during telemetry were representative of the later
movements of these individuals. Alligator 20145 was largely sedentary on
Payne's Prairie from 23 April to 21 May 1976. It was recaptured on 14
July 1976 approximately 200 m from its last contact, having moved an
average of 3.7 m/day in the interim. its weight had increased 210 gm
!26% initial) from 19 April to 14 July, indicating that food was readily
available and that the transmitter package (which was still attached)
had not interfered with feeding. Contact with alligator 20089 was lost
on Orange Lake on 21 October 1376, and regained when the individual was
recaptured 60 m from its lat krown location on 16 March !977. Weight
loss in the interval was 7. which was consistent with winter weight
losses recorded for juveniles of similar size, and the recapture location
suggested that little movement had occurred over the winter.
0 0 0
< S -0
CN NC Lft
Co N Co
CO O 0 O
The effects of habitat on growth rates of juvenile A. mississippiensis
are presumably related to food availability. Prey of small A. missis-
sippiensis consists largely of macroinvertebrates and fish (Fogarty
and Albury, 1967; Chabreck, 1971; Deitz and Hines, unpublished data).
The abundances and availability of these items must vary considerably
with water temperature, water depth and trophic state of the habitat.
Captive studies of young A. mnississippiensis have documented the relation-
ship between food availability and quality (measured via protein con-
version rates) and growth rate (Coulson et al., 1973; Joanen and
McNease, 1974). Food consumption by young alligators from brackish
marshes is less than that of alligators from fresh marshes, probably
leading to slower growth (Chabreck, 1971).
Growth rates of juveniles from other portions of the range of A.
mississippiensis are compared with those from north and central Fiorida
in Table 3-6. The high rates observed 'or souch Florida aliigators
presumably result from a reduction in or eliimination of the winter
dormancy period (Hines et aZ., 1968). Orange Lake alligators growing
for 12 monthss at the same rates observed for the 7 mcnth active season
would have an annual increment in total length of approximately 36 cm--
roughly the same growth as Everglades animals. Seasonal inf'ljences on
growth are also illustrate by Murphy's (;976) data from South Carolina,
where juveniles grew faster in artificiaiy heated portions of a lake
than in unheated parts (Table 3-6). Prey availability is undoubtedly
quite variable both within and between locales, as wei as seasonally.
Ln c In In ( I
S I0 .
S 1 3- >- >- >- > -
I- -0 .0 > >0 r
lU 0 -a C 3 : .C: OC
(o C L C a .
q) ) C 36n
-- C Z 3
* *^ U CU
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| *-' -1 2 Z 2 './ (^ v:
Growth rates for most other crocodiians have not been determined.
Growth rates (converted to increment in total length)of Crocodyius
vorosus in northern Australia averaged about 36 cm/yr for males and
33 cm/yr for females (Webb and Messel, unpublished data). Seasonal
variations were not as pronounced as in A. mississippiensis. Rates for
C. niloticus from east Africa reported by Cott (1961) from various
sources were slightly below the 31.7 cm/yr increase in total length
determined for captives. Other data for C. niloticus from Graham (1968)
suggest that sub-optimal habitat reduces growth considerably.
Males grow faster than females in Crocodylus porosus (Webb and
Messel, unpublished data), C. ni-otcius (Graham, 1968) and A. missis-
sippiensis (Mcllhenny, 1935). Differences in growth rates of Louisiana
A. osississipisnss are probably not significant until juveniles -each
at least 60 cm SVL (Nichols et at., 1976). My data suggest similar
conclusions for Florida alligators. Juvenile alligators are sometimes
difficult to sex; Hines et al. (1968) have reported 80% males in their
south Florida sample, a figure which they believed to result from
sexing errors. The sex ratio determined for north Florida juveniles
(1.59:1) is in excellent agreement with the sex ratios of Louisiana
adults (1.51:1- Chabreck, 1966).
Survivorship of juvenile crocodilians is unknown, but has been
widely assumed to be low. Popular and semi-technical accounts of A.
'mi;ssissFpn,,sis report mortality to be 30% or more for the first year
(Neill, 197!); tre few data available indicate that it may be signif-
icantly lower. My estimates probably represent ~ninimum figures for
survivorship, since many juveniles which .were known to be alive
(subsequently captured) were not captured or seen on some visits to
their pods. The two-year survival of 2 pods in South Carolina was
approximately .16 (Murphy, 1976), which is comparable to my figures.
Nichols et ai. (1976) estimated one-year survivorship of Louisiana
alligators to be .35 and two-year survivorship to be .21, although
no supporting data were provided for these estimates. The survivor-
ship of one Louisiana pod marked in 1921 was apparently at least .66
through 1927 (Mcllhenny, 1935). Quantitative data on survivorship in
other crocodilians are available only for Crocodylus porosus in northern
Australia, where the one-year survivorship of one cohort of 58 hatchlings
was at least .40 (Webb, 1977). Observations by Graham (1968) for C.
niloticus indicate that where habitat is unsuitable for juveniles (bare
shoreline) mortality may be nearly 100%.
While not statistically significant, the differences in survivor-
ship between habitats suggested differences in predation. This is
supported by the frequency of injuries, which, like mortality, was
highest in shallow marsh habitats. This pattern implies that wading
birds are an important predator; their access to small alligators is
probably much better in shallow marshes than in deep water areas.
Wading birds are known predators of other juvenile crocodilians such
as C .-ccdyItus niZoticus (Cott, 1961) and C. raZustrjis (Dharmakumarsinhi,
1947), and have been observed preying on juvenile alligators at the
Carr pond (Carr, pers. comm.). Droughts are more likely to increase
morality of marsh alligators aoove that of lake alligators (Nichols
et a.., i176); tnis could be by desiccation or result from increased
access oy predators. Drought mortality of subadults on Station Pond
in 1977 was severe (Hines, Woodward, and Deitz, unpublished data), and
Staton and Dixon (1975) attributed low survivorship of some Caiman
crocodilus in Venezuela to drought.
An age-related increase in the natural incidence of injuries
similar to that observed for A. mississippir~-~s appears to be typical
for other juvenile crocodilians as well. injuries to hatchlings and
juveniles less than about 1 m in total length have been assumed to
represent predation, while injuries to larger juveniles and adults
are attributed to social interactions and, possibly. attempted cannibalism
(Webb and Messel, 1977; Staton and Dixon, 1975). Fluctuating water
levels concentrate Caiman crocodilus populations and increase social
conflict (Staton and Dixon, 1975, 1977); this could account for the
higher frequency of injuries in marsh-dwelling A. mississipiensi-s.
However, alligator population densities on Orange Lake and Lake Griffin
were as high or higher than on Station Pond (Hines, Woodward and Ce;tz,
unpublished data), and the high incidence of injuries on Station Pond
was recorded prior to the 1977 drought. Evidence for significant
cannibalism in A. mississippiensis is likewise poor, as will be
discussed below (Chapter 5).
The movements of juvenile A. mississirpiensis in north Florida
correspond closely to those of Louisiana alligators with respect to
movement from nest to den, overwintering, and the initiation of dispersal
the Following spring 'Mcllhenny, 1935; Chabreck, 1965). Chabreck (1965)
has also described reduced movement of pods when nests are located
adjacent to dens, as well as the movement of pods to open water when
nests are situated nearby (similar to my lake fringe nests).
The importance of the female's guard pool or wallow in determining
post-hatching movements has not previously been emphasized. In addition
to possibly providing deeper (and cooler) water for the adult during
attendance of nests and young, the wallows may be important in providing
a small but locatable refuge in which young can assemble after hatching.
Pools created by females during movements of the pod to the den may
similarly aid in assembly, and function to minimize losses of stragglers.
While these pools could increase the chances of predator detection,
particularly by wading birds, this may be offset by the increased
visibility of young which they provide the attending parent. Smashed
vegetation provides basking sites for the hatchlings; in some areas
of marsh these are not readily available. Hatchlings in pools are
also able to disperse more during nocturnal feeding without entering
dense vegetation (see Chapter 4); this may facilitate foraging by in-
creasing range and also by improving access to insects which would
otherwise be unobtainable on plant stems above the water.
Dispersal of juvenile alligators during their first summer, followed
by returns to the den during the second winter or during droughts, has
also been reported by Chabreck (1965) for Louisiana and by Fogarty
(1974) for the Everglades. From comparisons of Lake Griffin and Orange
Lake, I suspect that pod dispersal is related to size in all habitats
and occurs more slowly if growth is retarded. However, mean movement
rates computed for individual recaptures (Table 3-4) did not correlate
well with growth rates. Movement rates of size class Iil juveniles
indicated that alligators of this size have lost permanent contact w;th
their natal areas.
Movement of immature alligators in Louisiana decreases from spring
through fall, with males exhibiting slight preferences for open water
areas and females for marsh (McNease and Joanen, 1974; Taylor et al.,
1976). Both sexes show wide variation in daily movement, and occasional
long movements (1 km) are regularly observed. My observations of
juvenile movements based on recapture data from Florida are consistent
with these patterns. Sex-related differences are not evident in
small juveniles in Florida; the juveniles tracked by McNease and Joanen
(1974) were larger (mean SVL 73 cm), which is probably significant.
Wallows or guard pools are also used by nesting female Crocodylus
pcrosus; the photograph by bb et a-. (1977) of a nest in northern
Australia shows wallows which appear identical to those used by A.
mississippiensis on Orange Lake. Small pools are also reportedly used
by adult C. pa ustris (Dharmakumarsinjhi, 1947) and C. niloio-Us
(Cott, 1961) in caring for their young. For C. nilcticus, use of these
pools may require overland movements of female and young from river
bank nests to suitable inland sloughs (Cott, 1961). The semi-permanent
habitat alterations produced by A. ississzippinsis in making dens
and trails (Mcilhenny, 1935; Craighead, 1968) have not been reported
for other crocodilians, although C. ni'lozti-us and azi7:an crccodyius
will deepen pools in response to drought (Cott, 1961; Staton and
Dixon, 1975). Parental care is sufficiently widespread in crocodilians
(see Chapter 4) that permanent nursery areas such as those used by
Station Pond a;llgators may be formed by the reproductive activities of
other marsh-dweli;ng species.
Australian Crocodylus porosus form creches (= pods) after hatching,
and in some cases these are moved or accompanied by an adult (presumed
parent) for several weeks (Webb et at., 1977). Subsequent dispersal of
C. porosus hatchlings occurs earlier than in A. rississippiensis, and
distances moved by one- and two-year old juveniles are much greater
(Webb and Messel, 1978). Tidal currents in the rivers where these groups
were studied are evidently significant, since there is some tendency for
animals to disperse downstream (Webb anc Messel, 1978). Medem (1971a,
b) has suggested that Paleosuchus palpebrcsus hatchlings, which generally
occupy swift streams, also disperse rapidly without forming large pods.
Occasional long distance movements similar to those observed in individual
A. misssissippiensis also occur in juvenile C. porosus, and these have
been postulated to represent excursions which are followed by returns to
a core area (Webb and Messel, 1978). Juvenile A. isssissippiensis
apparently possess homing abilities sufficient to allow such returns
(ChabrecK, 1965; P. Murphy, 1978; G. Rodda, unpublished data).
SOCIAL BEHAVIOR OF JUVENILE ALLIGATORS
The recent world-wide interest in crocodilian conservation has
resulted in many new observations of crocodilian behavior. Enough infor-
mation on adult social behavior has accumulated for 3 species (.4Aigator
miss ssippiensis, Crocodylus acutus, and C. nitotiv-us to support valid
interspecific comparisons (Garrick and Lang, 1977), although compre-
hensive field studies of adult behavior such as Modha's on C. nitoticus
(1967) are still lacking. Attempts to breed most crocodilians in
captivity have produced surprising new data on nesting and parental care
(e.g., Alvarez del Toro, 1974; Hunt, 1975; Pooley, 1977) and suggest
that recently discovered behaviors such as parental transport o: young
in the mouth may be a consistent feature of the order.
Descriptions of juvenile social behavior ir. :rocodil:3ns usually
have been confined to observations that the young of most species remain
in groups for some period after hatching. Vocalizat:ins have been
presumed to be important in maintaining chese groups (Campbeli, 1973),
but the actual maintenance behaviors and duration of groups have not been
systematical 1 studied. While some parental care of groups of ycurg
has been regularly observed in captivity, the consistency, durration ard
significance of oarentai care 'n wild croccdilians are !argely unknown.
Parental care for 5 weeks after hatching has been reported for Ccrccdylz..
acutus by Alvarez del Toro (1974); Cott (1971) has observed 12 weeks of
post-hatching care in C. niloticus.
Mcllhenny's (1935) observations of 4. mississippiensis indicated
that pods persisted until the following spring, suggesting that they
were actively maintained, and were protected by the parent female through-
out this period. These observations were impugned by Neill (1971).
However, both Chabreck (1965) and Fogarty (1974) also reported pod
persistence for one year, and Kushlan (1973) provided unequivocal
evidence for maternal protection of the young. The objectives of this
portion of the study were to obtain additional data on the social behavior
of pods and the frequency of parental care and, by examining pods in
different locales, to determine the extent to which these might vary
with habitat. The significance of vocalizations in maintaining pods
and mediating parental care was also investigated.
General locations of pods were determined as in Chapter III.
Diurnal observations of pods were usually nade with binoculars from
within 10 m; small alligators could be observed successfully without a
blind from this distance if observer movements were reduced to a
minimum. Temporary blinds were occasionally used, but frequent:
position shifts by pods made their regular use impossible. Juveniles
were also successfully observed from na airboat seat; it appeared that
movements made high (2 m) abcve the water surface were not easily
detected. Detailed observations of nocturnal behavior proved impossible.
Passive night vision equipment (starlight scope) was used on several
occasions, but resolution and image intensity were both too poor to
distinguish juvenile alligators from emergent vegetation. General
movements and behavior of juveniles after dark were recorded by flashing
a headlamp beam at regular (usually 15 minute) intervals and noting
positions and any other activity of alligators visible. Eyeshines
(reflections from the tapetum lucidum) were helpful in locating alligators
in dense cover. Flashes of 15 seconds or less appeared to have little
effect on movements or rates of vocalizations; longer flashes seemed to
produce some avoidance and cover-seeking behavior and were avoided.
Some nocturnal observations were made by covering a headlamp with a
red filter (auto taillight cover). This light had limited range and
produced dim eyeshines at best, but it was also far less disturbing.
Many individuals appeared entirely unaffected and continued to move and
feed in an apparently normal fashion while the red light was on.
Positions of individual juvenile alligators during the day were
recorded at regular intervals. Each animal was scored as: 1) moving or
stationary; 2) on land or in the water; 3) in the sun or shade; and 4)
under cover or in the open, i.e., relatively exposed when viewed from
above. Verbal descriptions of important physical features as well as
field sketches were made to assist in plotting movements. Individual
recognition was possible for some juveniles that had anomalies ;n their
The vocalizations produced by hatchling alligators have been
referred to as grunts by Campbel; (1973) and Herzog and Burghardt (;977'.
These grunts were quite audible at most distances from wrich I observed
pods. Grunts frequently occurred in bursts of one or more single grunts
produced in rapid succession by one individual; following Herzog and
Burghardt (1977) each of these groups of grunts was counted as a single
series. The number of vocal series produced during each 10 or 15 minute
period was tabulated; if the individual vocalizing was seen, context
was also recorded. Each pod received a score for number of vocal
series/alligator-hour (VAH) for each period, calculated in the following
#VH = vocal series during the observation period
(# juveniles known to be present)(period length in hours)
Differences in frequency, intensity and location between vocalizations of
different individuals were such that scoring was difficult only if a
large number of individuals were vocalizing simultaneously. Tape
recordings of vocalizations were made with an AKG 451E directional
microphone and a Nagra 1113 or Tandberg Model 11 tape recorder, and
analyzed with a Kay Sonagraph (Model 7029A).
At sunrise, small alligators were in the water, usually in dense
cover such as emergent Cla~im or Pontede-ia stands. Little activity
was evident at this time: those alligators which were visible remained
motioniess and seldom vocalized. Emergence from cover tegan about one
hour after sunrise (Figs. 4-lb and 4-2b), and appeared to depend on
illumination by the rising sun of portions of the small coves where
hatcn!;ngs were located. Prior to emergence, a few juveniles would
begin to swim abouz and emit low intensity juvenile grunts. The number
16 SEPT. i977
SUNRISE AT 0714
18 ANIMALS OBSERVED
| basO 1 move to shade
SMorning emergence by ha:chling alligators in
S \/ \
So inH .
23 SEPT. 1975
75 CDI POD
l i I I I
Morning emergence by hatching alligators
on Payne's Prairie.
of grunts by seen and unseen hatchlings rose rapidly at this point
(Figs. 4-la and 4-2a). As most alligators in a group began to vocalize
sporadically, the first few individuals emerged from cover and climbed
out of the water onto tussocks or clumps of vegetation in the sun,
grunting regularly as they did so. The rest of the pod followed
immediately, climbing out into the sun while grunting. Most of these
hatchlings used the same tussock or clump of weeds as the first
individuals to emerge. Alligators ceased vocalizing once they had climbed
out of the water and moved onto a suitable basking spot. At the time of
emergence, site air temperatures were almost always equal to or greater
than water temperatures.
The movement of the group from aquatic cover to terrestrial
basking sites usually took less than 30 minutes and was often completed
in 15 minutes (Figs. 4-1 and 4-2). As indicated above, alligators
oriented to basking spots already occupied by other pod members, even
though there were often many other apparently suitable sites nearby.
This resulted either in one large aggregation of basking alligators
within an area sometimes as small as I m or if small clumps of emergent
vegetation were being used, in two or three smaller groups adjacent to
each other. Hatchlings that remained in the nursery pool by the nest
Frequently basked on the base of the nest; those which had moved into
other pools used vegetation which had been flattened down by the
female's body. If the female was present and remained stationary ;n
Che sun, hatchiings sometimes used her head and oack as basking sites.
Cloudy skies or cool temperatures delayed or inhibited this
coordinated morning emergence. I made no systematic observations of
pods in mid-winter but hatchlings which were observed basking at this
time of year were as tightly bunched as on other occasions.
Following morning emergence, juvenile alligators basked for varying
periods; the duration of those was probably dependent on individual
thermoregulation. For most hatchlings, the period on land lasted about
2-2.5 hours, and included movements between sun and shade (Figs. 4-lb
and 4-3). Little movement and few vocalizations were evident in the
group during this period; VAH for 8 pods observed on 14 sunny days
averaged 2.3 + 1.7. Alligators were quite tolerant of being stepped on
or jostled by other juveniles while basking, and it was not uncommon to
see individuals basking with the heads or tails of others lying across
their backs. Some hatchlings appeared almost comatose, and were observed
to lie motionless and fully exposed to the sun for 30 minutes cr more
with their eyes closed. Hatchlings would also occasionally climb up
the stems of emergent vegetation, especially Cladium j~eaioensiz, while
basking, and observed some that had climbed more than 30 cm above the
After basking, hatchlings moved into shady areas on land or in the
water (Fig. 4-4). These movements were accompanied by sporadic vocal-
izations. Whiie movements off of the basking platforms were not as
concerted as emergence, most alligators left within about 1 hour of
one another; this usually took place from 4 to 5 hours after sunrise
(see Figs. 4-3 and 4-4). Overheating may nave been the principal
stimulus for these movements, since the alligators selected cooler
areas and air temperatures at this time often exceeded 30'C. However,
I rarely observed obvious behavioral therroragi!atory responses, such
* *" (
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as postural adjustments, that would support this supposition; gaping
was only rarely observed. Some hatchlings and larger juveniles yawned
briefly once or twice before entering the water, but this also was
During warm weather, young alligators spent most of the remainder
of the day in the water, generally remaining under the cover of floating
or emergent vegetation and moving occasionally. As noted above, basking
was prolonged in cooler weather. Throughout the afternoon some alligators
climbed out of the water to bask briefly or to lie in the shade, but
there appeared to be no group coordination to these movements and most
pod members remained in the water (Fig. 4-3). Short movements by
individuals gradually dispersed the pod as the day progressed, and the
hatchlings were never as densely aggregated as during the morning basking
period. Vocalizations were few; VAH for the midday sunset period
averaged 2.4 + 1.3. Although alligators were relatively inactive, chey
responded readily to potential prey and feeding strikes were regularly
observed at all hours. By sundown, all individuals in a pod were
normally in the water, under cover and largely motionless.
Immediately after sundown there was an increase in activity which
duplicated the morning emergence in its rapid, synchronous onset. The
number of alligators moving and grunting rose steeply over a 15 minute
period, and as these juveniles began swimming around they also emerged
fro- cover. Figs. 4-5 and 4-6 are representative temporal plots of the
rate of vocalization by the pod (VAH) and number of alligators visible
to me. In Fig. 4-5 grunting peaked before most of the pod became
3181SIA 'ON 1!VIOl
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318ISIA d38JvnN -1VI01
visible--it appeared on this occasion and others that hatchlings began
swimming about while vocalizing and then emerged from cover. An
increase in feeding strikes was also associated with these increased
movements and feeding continued as the pod rapidly dispersed. Alligators
vocalized as they moved, and for the first hour after sunset mean VAH
was 8.8 + 6.9, significantly higher than mean VAH observed for the morning
or afternoon (p < .01, t-test). Thereafter, vocalizations declined; this
was coincident with a decrease in feeding activity and swimming move-
Figures 4-7 and 4-8 are representative plots of the positions of
most of the members of one pod on Orange Lake during nocturnal emergency
The rapid dispersal following emergence is evident. The limits of
dispersal were approximated by the end of the first hour after sunset,
although some individuals continued to move away from the center of
the group for the next few hours. By 0030 hours feeding activity had
ended, and alligators had moved into or adjacent to vegetation along
the nearest shoreline (mostly Hydrocotyle umbellata in Fig. 4-7).
Little additional activity was seen until 0445 hours when the hatchlings
began returning to their initial emergence point, disappearing into the
vegetation when they arrived. In contrast to most other movements,
these were not accompanied by an increase in vocalizations. By C615
the distribution of the pod had contracted to a 20 m strict of shoreline
and a small cove (Fig. 4-8); this was a normal scatter for hatchlings
in the morning prior to emergence.
On subsequent nights, the pod depicted in Figs. 4-7 and 4-8
deployed over approximately the sarime area each evening, and regrouped
SUNSET at 2026
S12 VISIBLE 15 VISIBLE
S16 VISIBLE 18 VISIBLE
ax 0 7 x\ k
Figure 4-7. Evening deployment of foraging juvenile alligators
on Orange Lake (continued on Fig. 4-8).
LE 14 VISIBLE
.E 6 VISIBLE
Return of foraging juvenile alligators to their initial
emergence point on Orange Lake (continuation of Fig. 4-7).
in the same refuge the next morning. Concurrent observations of 3
other pods on Orange Lake indicated that this was a typical pattern.
Observations on Lake Griffin were not as detailed; however, pods there
did show the same sort of expansion early in the morning followed by a
retreat under cover and, still later, a contraction in area covered by
0200 hours. Small alligators on Lake Griffin did not venture as far
from shore as similarly-sized animals on Orange Lake, possibly because
weedy cover was not as abundant.
Water depths at the site of Fig. 4-7 and 4-8 and in marshy areas
where other pods were located were usually 60 cm or less. These shallow
areas cooled rapidly at night, and were often below 25C before mid-
night. This drop in water temperature was probably one factor influenc-
ing the reduction in feeding activity of small alligators. However,
reduced feeding activity after midnight was also observed in pods
located in deeper water areas of Orange Lake and Lake Griffin, where
water temperatures remained above 280C throughout most of the night
during the summer months.
Alligators did not exhibit nocturnal dispersal for the first
few weeks following hatching, but did spread out at night once they
reached larger pools in the marsh or lake shoreline. Pods expanded more
at night as individual body size increased. Hatchlings in October
following hatching, SVL 14-17 cm, were rarely found more than 10 m
from cover and the maximum spread of a pod at night did not exceed
20 m of shoreline. Pods appeared to disperse more each night as air
and water temperatures increased in the spring, and by June dispersals
such as that shown in Fig. 4-7 and 4-8 were typical. Most juveniles ;n
all habitats measured 19-23 cm SVL at that time (see Chapter ill).
Pod cohesion began to disappear in mid to late June of the year
following hatching, although this was a gradual phenomenon (see Chapter
III). There were no consistent individual associations in the sub-groups
formed at this time. Some social basking in the morning was observed, but
not all individuals basked in the same small area, and vocalizations
during emergence were much reduced; the latter was also true for nocturnal
emergence. Distributions of juveniles in all localities following their
second winter suggested solitary behavior, although these alligators
were much warier and harder to observe during the day than younger
juveniles. The activity of these larger juveniles appeared to be about
the same as that of hatchlings, without the same level of group co-
ordination; juveniles emerged from cover in the morning to bask, returned
to the water and moved little throughout the day, and finally emerged
at sundown to feed.
Juvenile grunts were emitted by hatchlings in a variety of contexts.
As discussed above, increases in the average number of vocalizations by
individuals in a pod were associated with morning and evening emergences
from cover. While these synchronous emergences produced the most
striking changes in rates of vocalization, grunting increased in almost
every situation which involved increased movement by and/or disturbances
to the pod. Such situations included: the arrival, departure or move-
ment of an adult alligator through the pod; increased movements
associated with feeding; separation of individuals from the pod; and
artificial disturbances created by my observations or manipulations.
Context for many grunts was not recorded because it was frequently
difficult to determine which of several alligators in a small aggregation
had vocalized. The association of grunting with movement was pronounced.
Of 589 vocal series produced by undisturbed pods, 67 (11.4%) were given
by stationary hatchlings, 273 (46.3%) were given by moving alligators,
and 249 (42.3%) were given by alligators which were either moving or
adjacent to moving animals (i.e., the identity of the vocalizing individual
in this last category was uncertain, but the vocalization was associated
with movement by a juvenile alligator). Hatchlings on land rarely
vocalized except when emerging from or entering the water, and VAH
during daylight hours was positively correlated with the proportion of
alligators in the water (r = .43, p < .01, n = 55 observation periods).
The increases in VAH observed during both morning and evening
emergences were associated with increased swimming activity and other
movements by individual hatchlings in the pod. The vocalizations pro-
duced during morning emergence appeared to attract pod members to a
single area where a synchronous emergence followed by basking took
place (social bask). Basking individuals were stationary, and vocalized
During evening emergence, individuals grunted frequently as they
dispersed and continued to grunt irregularly as they foraged. Single
grunts rather than vocal series of two or more grunts were often emitted
by ttese foraging juveniles; there was a significant difference in the
number of grunts per series between alligators vocalizing during the day
and chose vocalizing at night (Fig. 4-9).
Hatchlings that made feeding strikes during the day would also
grunt while foraging. Foraging movements and grunting by these alligators
n = 230 series
! 2 3 4 5 >5
n = 365 series
i grunts/series = 2.0
3 4 5 )5
Number of grunts/series emitted by juvenile
alligators during the day and at night.
were sometimes followed by similar behavior in nearby juveniles. One
hatchling which had captured a large sphinx moth (Sphingidae) larva was
pursued for more than 5 minutes by two other juveniles that grunted
repeatedly. One of the purusers succeeded in obtaining a piece of the
larva. During the chase 10 additional hatchlings emerged from cover;
most of these individuals began foraging as they emerged.
There was one significant exception to the generalization that
juvenile alligators increased their rate of vocalization while moving.
During reaggregation just before dawn following the previous night's
dispersal (Fig. 4-8), juveniles returned to their emergence point in
silence. Some juveniles also responded to disturbances after dark by
moving silently under cover; these movements were also directed toward
the initial emergence point, and nocturnal disturbance of a dispersed
pod generally resulted in a net reduction in the area occupied by the
pod as members all returned to the same area.
During the daily movements of the pod, hatchlings often became
separated from the main group, sometimes by as much as 10 m. !n the
dense cover occupied by most pods, this resulted in loss of visual
contact. Vocalizations by isolated juveniles 4ould often be answered
by one or more alligators in the main group. If answered, isolated
individuals lifted their heads and oriented them toward the response.
They would then begin to move toward the rest of the pod, grunting as
they moved; their vocalizations usually received answering grunts.
Isoalted hatchiings continued moving and grunting until they had
rejoined the pod. To test this ability to locate pods under field
conditions, 1 released three hatchlings (on separate occasions) 10-15 m
away from non-sibling pods in locations unfamiliar to the released
juveniles. All three hatchlings correctly oriented to grunts produced
by members of the pods and moved directly toward them, vocalizing as they
did so. Dense emergent vegetation in all three areas made visual contact
by individuals more than 2 m apart extremely unlikely, and vocalizations
appeared to be the only clue used by the transplants in locating the new
pods. After joining the pods, at least 2 of the 3 released juveniles
remained with them, for a minimum of 2 weeks and 9 months, respectively.
The arrival of what appeared to be the parent female alligator also
resulted in brief increases in grunting by the pod, and I was frequently
alerted to the presence of an adult alligator by the grunting of the
juveniles. Movements of the female while with the pod also provoked
grunts. During my only daylight observation of a female moving with
her pod, the hatchlings were vocalizing regularly as they followed her.
Pods that detected my approach during the day responded by grunt-
ing rapidly and retreating into nearby cover, often submerging as they
swam away. Response to predators was assumed to be similar. No group
coordination was evident, and the pod normally became scattered as a
result of such disturbances. Continued disturbance of pods after dark
also resulted in scattering of individuals. Juveniles normally re-
emerged from cover 15-30 minutes after the disturbance had ceased.
These emergences were very similar to those of morning and evening,
in thac decreased grunting preceded the actual movement of individuals
out of weedy cover. Hatchlings continued to grunt as they emerged,
and responded to vocal or visual contact with siblings by moving
toward them; this resulted in a reaggregation of the scattered pod.
If basking had been interrupted by the disturbance, most juveniles
returned to land.
Various stimuli increased the intensity and rate of grunting by
individual juveniles. Individuals which were swimming slowly about or
foraging emitted soft, infrequent grunts such as those represented in
Fig. 4-10, while hatchlings responding to my approach or the approach
of an adult alligator produced louder grunts, such as those in Fig. 4-11,
at a more rapid rate. These variations between grunts in different
contexts were continuous, and as noted by Herzog and Burghardt (1977)
the grunt appears to be a graded signal. A difference in frequencies is
also evident from a comparison of Figs. 4-10 and 4-11. Grunts emitted
at greater intensities began at higher frequencies before a rapid down-
sweep, and harmonics were more evident. The most intense and most
rapidly repeated grunts were those emitted in "distress" contexts
(Fig. 4-12; see also Herzog and Burghardt, 1977, Fig. 2). This "juvenile
distress call' has been referred to as distinct from the grunt by
several authors (&.g., Neill, 1971; Herzog and Burghardt, 1977, Staton,
1978). However, I was unable to detect consistent differences between
sonagrams of grunts recorded in distress contexts and grunts recorded
in other contexts, including those produced prior to hatching (Fig.
4-13); furthermore, experimental evidence (see below) indicated that
juvenile alligators had similar difficulties. For convenience, these
high-Intensity, rapidly repeated grunts were referred to as distress
calls by virtue of the context in which they were often emitted--not
because of any unique characteristics of the signal (see Campbell,
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Distress calls were emitted in rapid succession when juveniles
were alarmed by my approach and when they were captured. In some
instances, they resulted in the approach of adult alligators, assumed
to be the female parents (see below). The behavior of other juveniles
upon hearing calls emitted in these contexts was quite variable; my
observations were complicated by the fact that it was often impossible
to determine whether the alligators were responding to the distress calls
or to the original disturbance. Many juveniles, whatever their sub-
sequent behavior, vocalized in response to distress calls (as did many
in response to juvenile grunts). Some juveniles appeared to be alarmed,
and responded by submerging or by swimming or running into cover.
Others responded by moving toward the source of the calls. This last
response was so consistent that it was sometimes useful in capturing
juvenile alligators. Distress calls of captives could be elicited by
squeezing them or by agitating the bag in which they were being kept;
many of the remaining pod members would then emerge from vegetation
and approach. Older juveniles could also be attracted in this fashion,
although not as regularly as hatchlings. Submerged hatchlings surfaced
in response to calls of hand-held siblings, indicating that the calls
were audible underwater.
Although vocalization appeared to be of great importance in main-
taining pod cohesion, visual contact was clearly an important close
range signal. Moving hatchlings 4ere often followed closely by other
hatchlings. As noted above, the first hatchlings to emerge from cover
in the morning were followed by the remainder of the pod. Juveniles
normally swam with only a small portion of their back exposed; they
were never observed to inflate sufficiently to expose more than this.
The distal half of the tail was allowed to protrude, so that both the
head and tail of hatchlings which were swimming or resting in the water
were visible above the surface. This posture was identical to the
head-emergent tail-arched posture described by Garrick et ai. (1978)
for adult A. mississippiensis. In hatchlings, the posture was probably
used to increase visibility of individuals to other pod members or to
the parent; it appeared to have no other social significance. The tail
was submerged and only the head was visible when hatchlings were alarmed
or concealed under cover.
No structured social organization was evident in pods. Those which
emerged first to bask were different individuals from day to day. Hatch-
lings were extremely tolerant of close contact. An individual would
occasionally grunt if stepped on, but more frequently would either
ignore the disturbance or move over.
By July of their first year pods of juvenile alligators were much
warier of my approach and more difficult to observe as a group following
dispersal. Consequently I have no quantitative data on rates of grunt-
ing in different social contexts by animals older than 1 year. Yearlings
and older juveniles which were observed feeding at night vocalized
rarely; this was markedly different from what was observed for hatch-
lings. Yearlings were heard grunting during emergence from the water
to bask, when approaching or approached by an adult alligator, and when
startled by my appearance. They also grunted while swimming with small
groups of other yearlings; vocalizations in this context appeared to be
used to maintain contact since these individuals answered each other's