Behavorial ecology of young American alligators


Material Information

Behavorial ecology of young American alligators
Physical Description:
vii, 152 leaves : ill. ; 28 cm.
Deitz, David Charles, 1951-
Publication Date:


Subjects / Keywords:
Alligators -- Behavior   ( lcsh )
Alligators -- Florida   ( lcsh )
bibliography   ( marcgt )
theses   ( marcgt )
non-fiction   ( marcgt )


Thesis--University of Florida.
Includes bibliographical references (leaves 144-151).
Statement of Responsibility:
by David Charles Deitz.
General Note:
General Note:

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Source Institution:
University of Florida
Rights Management:
All applicable rights reserved by the source institution and holding location.
Resource Identifier:
aleph - 000090202
notis - AAK5592
oclc - 05780726
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Full Text








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me to use their unpublished data.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.



ABSTRACT . . . .




Orange and Lochloosa Lakes. .
Payne's Prairie .
Lake Griffin. . .
Station Pond .


Introduction. .
Methods . .
Results . .
Discussion. . .


introduction . .
Methods . . .
Resu lts . . .
Discussion. . . .


r.troduction . .. ..
Methods . . .

Discussion. . . .


BISGRAPICAL SKET'CH....................

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



David Charles Deitz

June, 1979

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 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 of the N*lius

in 1608.

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

field studies.

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. 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

Depth (m)



< 1

0.4 0.9



> 1

Area (ha)







ca 5

Trophic State Index
4.3 Mesotrophic

5.2 Mesotropnic

13.7 Hypereutrophic

(3.6 Mesotrophic)

7.4 Eutrophic

14.7 Hypereutrophic

Values for mean depth and trophic state index are from Brezonk and
Shannon (1971) except values from Payne's Prairie which are from
White (1974).

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

1 3
^^/ \ 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.



U- t








rs E








(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,

unpub. data).

Payne's Prairie

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.


17.6 7


S17.4 -
172 -
> 17.0-
S16.6 -

, 16.4
-J 16.2-
J 16.0-

1 I5.8-


'MJJ .AE % ~ j! I J I ~





...'%.. / r

UnAIU~t LAt- ---



1975 1976 1977

Figure 2-3.

Water levels at three study sites, 1975-1977: Payne's
7rairie, top; Orange Lake and Lake Griffin, bottom.

' I
\ I


18.0 1


6 17.64

- 16.4-






Lake Griffin

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, 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;

Table 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

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

as appropriate.



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 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.

Data Analysis

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


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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

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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;

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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


SVL ) 31 CM

Frequency of injuries in alligators from
lake and marsh habitats in north and
central Florida.



figure 3-3.

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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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


I Sap

. '"--DEN

Small pool
.,- 30 Aug-14 Sep'76

24-30 Aug'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 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

100 m


2172 POD
hatch Sept'75
72 recaptures


-; -' mi rsh ) --

IV *P'!
Ot,- _-/-_-". -' =--^S
-a- 2

May '77


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--"-. _-^ -- -'-,

17,28 Sep'-767

20 June '77

2 Nov'77



I I mo, 6




NEThtce 7Ag7

*Z Sep- 14Oc'
..7# Apr4.7

8-1 Ma'

'a-a- /
. -

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Figure ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ EThace 3-P ipes(r)"cMug70fa o rne ae 37-37

2539 pod


200 M

One capture from
75 LGI pod
Sep '76 Av

Sep '77

One year
75LGI pod- Sep'76
2533 pod- Sep'77

Figure 3-!0.

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

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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.

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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.


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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).



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

banding patterns.

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).


Activity Cycle

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




I emergence

Figure 4-1

| basO 1 move to shade

SMorning emergence by ha:chling alligators in
Orange Lake.



S \/ \

\I \
\/ X
no. visible

So inH .


23 SEPT. 1975

l i I I I

Sno. visible

0900 1000


Figure 4-2.

Morning emergence by hatching alligators
on Payne's Prairie.

0 75

Z 50

0 25

S20 LL


!0 0


c, -


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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

water surface.

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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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

JUNE 5,1977
SUNSET at 2026
2045 2!2055

x I

2130 2215


ax 0 7 x\ k


\ 3

Figure 4-7. Evening deployment of foraging juvenile alligators
on Orange Lake (continued on Fig. 4-8).

Figure 4-3.

JUNE 6,1977

S 0245

x x



0600 -0615



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
7 grunts/series=2.3

! 2 3 4 5 >5

1 2

Figure 4-9.

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