Front Cover
 Back Cover

Group Title: Bulletin of the Florida State Museum
Title: The cottonmouth moccasin on Sea Horse Key, Florida
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00001523/00001
 Material Information
Title: The cottonmouth moccasin on Sea Horse Key, Florida
Series Title: Bulletin of the Florida State Museum
Physical Description: 227-272 p. : illus., maps. ; 23 cm.
Language: English
Creator: Wharton, Charles H
Publisher: University of Florida
Place of Publication: Gainesville
Publication Date: 1969
Subject: Agkistrodon piscivorus   ( lcsh )
Snakes -- Florida -- Seahorse Key   ( lcsh )
Genre: bibliography   ( marcgt )
non-fiction   ( marcgt )
Bibliography: Bibliography: p. 270-272.
General Note: Cover title.
Statement of Responsibility: by Charles H. Wharton.
 Record Information
Bibliographic ID: UF00001523
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: ltqf - AAA0833
notis - ACK3725
alephbibnum - 000443064
oclc - 00590510
lccn - 75632030

Table of Contents
    Front Cover
        Page i
        Page ii
        Page 229
        Page 230
        Page 231
        Page 232
        Page 233
        Page 234
        Page 235
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        Page 237
        Page 238
        Page 239
        Page 240
        Page 241
        Page 242
        Page 243
        Page 244
        Page 245
        Page 246
        Page 247
        Page 248
        Page 249
        Page 250
        Page 251
        Page 252
        Page 253
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        Page 266
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        Page 270
        Page 271
        Page 272
    Back Cover
        Page 275
Full Text








Number 3

Charles H. Wharton




lished at irregular intervals. Volumes contain about 300 pages and are not neces-
sarily completed in any one calendar year.

,; W_;.t IvA-. .


Consultant for this issue:


Communications concerning purchase or exchange of the publication and all
manuscripts should be addressed to the Managing Editor of the Bulletin, Florida
State Museum, Seagle Building, Gainesville, Florida 32601.

Published 31 December 1969

Price for this issue $.80



SYNOPSIS: From 1954 to 1957 the author studied the cottonmouth moccasin
(Agkistrodon piscivorus) population of the islands near Cedar Key, Levy County,
Florida. Sea Horse Key, one of the outer islands, approximately 1 mile long and
7 miles from the mainland, then supported a total population of roughly 600
The cottonmouths aggregate under the breeding colonies of cormorants and
herons on the outer Cedar Keys and scavenge the fish the birds drop accidentally
from their nests. After post-nidal feeding stops in August, they eat birds, rats, and
squirrels. An abundant skink is the principal food of young cottonmouths.
The bird rookeries control distribution and food habits of three-fourths of
the island's snakes, serving snakes up to 150 meters distant. Activity ranges are
remarkably small (males average 0.43 acre, females 0.35 acre). Although the
main ridge lacked rookeries, ranges were similar. No evidence of territoriality
was found. Snake Key rookeries also support a large population of cottonmouths.
Atsena Otie and North Keys have no rookeries and few cottonmouths.
Island snakes den in shallow stump holes and under debris. Frequent warm
winter periods make emergency demands on stored fat, and 77 per cent of Sea
Horse Key snakes are in danger of starvation during winters with a mean tem-
perature of 16.3C, compared to 36 per cent of the fatter snakes on Snake Key.
The fat bodies of snakes apparently function as reserve food during periods of
high temperature. Fat-body weights, length/weight ratios, and feeding behavior
suggest that Sea Horse snakes are at a critical survival level. When removed from
their winter dens, cottonmouths apparently shun all holes for periods of up to 2
years; a persistent site memory is postulated.
At lowest cloacal temperatures (4.00C) cottonmouths are passive; they are
able to strike at 4.50C, crawl at 12.5C, and feed at 14.5C. Variation in ob-
served rates of heating and cooling suggests some physiological control. Up to 36
per cent of cottonmouths showed aggressive behavior at low temperatures con-
trasted to 4.1 per cent at high readings (21C and above).
The major cause of mortality is starvation. Adults have no enemies other
than linguatulid parasites and man. Two healthy and apparently genetically
eyeless snakes indicate the relative importance of olfaction in the island environ-
ment. The ambithermal cottonmouth, with its endogenous biennial sexual cycle,
its vagile nature, and its keen olfaction seems well adapted to preempt the island
niche of a terrestrial carnivore-scavenger.

'The author is Professor of Biology at Georgia State College, Atlanta,
Georgia. He submitted an earlier version of the material presented here to the
University of Florida in partial fulfillment of the Ph.D. degree (1958).

Wharton, Charles H. 1969. The cottonmouth moccasin on Sea Horse Key, Flor-
ida. Bull. Florida State Mus., vol. 14, no. 3, pp. 227-272

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swimming (at Snake Key). Kirk Strawn, who studied marine life
on the flats around Sea Horse Key, never saw a cottonmouth in salt
water. I worked the shore of Sea Horse Key many times on foot and
by boat, both day and night, and I never saw a cottonmouth swim-
ming in the salt water other than when they were provoked by
handling. Nor have I seen any signs of snakes moving to or from the
beach. Sometimes cottonmouths coil at the strandline; presence of
cover, beach-scavenging rats, or an activity range adjoining the beach
may explain these instances. I found no instance of their feeding on
fish that could not be attributed to the nesting, feeding, or roosting of
birds. That these snakes do not directly exploit the plentiful fish life
in the shallow, calm waters of Sea Horse Key is difficult to reconcile
with the habits of the cottonmouth on the mainland.
Only a few notes have been published on marine island cotton-
mouths. Sass (1926) thought that cottonmouths on the Isle of Palms,
South Carolina, rarely, if ever, fed on marine fishes. Wood (1954)
noted mass migration from Virginia's barrier islands to the mainland.
Carr (1936) and Wharton (1958, 1960, 1966) have made the only
previous reports dealing directly with the Cedar Keys cottonmouths.

This study was made possible by the cooperation of Kent Myers and other
personnel of the Refuge Division of the U.S. Bureau of Sports Fisheries and
Wildlife. For guidance during the course of this study I am especially in-
debted to the faculty of the Zoology Department, University of Florida, particu-
larly J. C. Dickinson, Jr., and Archie Carr. E. Lowe Pierce, Director of the Sea
Horse Key Marine Biological Laboratory, extended me many courtesies and
transportation through his caretaker, Doyle Folks of Cedar Keys. John N. Ham-
let kindly allowed me the use of his boat for the first half of my study. I ac-
knowledge the secretarial and other assistance of Carol Ruckdeschel and Patricia
Parker provided by the Biology Department of Georgia State College, and
of Taylor Murray of the Georgia State computer center.

Most of the cottonmouths occupied the island's western end. The
thick vegetation made it necessary to cut trails through this area, and
206 trail stations were designated with stamped aluminum tags nailed
on trees at 25 meter intervals (Fig. 3).
Snakes were approached carefully and restrained gently by a
leather noose around the neck. By the use of subcaudal scale-
clipping, (Blanchard and Finster, 1933), 402 cottonmouths were
marked individually. These afforded 510 recaptures, counting dissec-
tions, and a total of 545 individuals were handled. Data recorded on




a keysort card for each capture included length, weight, cloacal tem-
perature, and heart rate (if the specimen was quiet). Nearby soil,
air, and leaf mold temperatures, humidity, body position, behavior

165 .4',- -. 162 0 50 100
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*I 2-'- /8 7 METERS
129 87
125 ..
0 91V30\0 1 0 150
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O INLET '* ';
S 75.2* 200 I / (\
C17 79 ---
S00 / 31006
193 206 LAGOON --
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0 179 9 05> ,x \
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.-- ~e5 ---1 149

4041 149N
FIGURE 3. Sea Horse Key trail system. Points are stations 25 meters apart.
Stations 1-30, high ridge of island. Dashed line, edge of mangroves.

(activity in which the snake was engaged), and demeanor before
noosing were also noted.
For estimating the size of cottonmouths found dead in the field the
largest vertebrae and ribs were compared with a skeletal series of 33
specimens of known size and weight.
Cloacal temperatures were taken with Schultheis rectal thermom-
eter; soil and air temperatures with either the Schultheis instrument
or a standard mercury thermometer. A maximum-minimum ther-
mometer was kept at ground level in the forest of the central ridge
throughout the study. Temperature and humidity in den cavities
and in adjacent microclimates were taken with a battery-operated
Aminco instrument with a temperature-humidity probe.

While records of snake aggregations in the literature apply chiefly


Vol. 14


to denning such as the record by Noble and Clausen (1936), or to
unusual concentrations of snakes caused by factors such as rising
water (Slevin, 1950), one of the most spectacular and seldom docu-
mented aggregations of vertebrate life is that brought about by the
odorous and noisy bird rookery. With the fragility of the nests of
many wading birds and the frequency of dropped eggs, fish, and fallen
nestlings, a variety of scavengers and predators find bird colonies a
happy hunting ground. Host (1955) reports a gathering of alligators
near a large rookery of herons and ibises in the Everglades. Nor is
this food source ignored by mammals, including man. I have a report
that over 20 jaguars aggregated under a great jabiru stork rookery in
central South America in 1955. Austin and Kuroda (1953) describe
the remarkable instance of humans subsisting on salmon dropped by
cormorants and herons nesting around the Suruga Shrine in Aomori
Prefecture, Japan.
The cottonmouth, by virtue of its adaptability to almost any avail-
able food source, dead or alive, becomes a resourceful opportunist
when bird rookeries are nearby. Here it scavenges beneath the nest
trees, apparently attracted by the odor of the excreta and the fish re-
gurgitated by annoyed parent birds or dropped by clumsy nestlings.
Chapman (1908) was one of the first to note what may have been
aggregating cottonmouths under a nesting colony of anhingas and
lieroni near St. Lucia, Florida. In the early 1920's, Sass (1926), on
the Isle of Palms near Charleston, South Carolina, saw scores of cot-
tonmouths gathered under a great blue heron "village" apparently
attracted by dropped fish. Host (1955) noted many cottonmouths
bnci ath a large rookery on the edge of Lake Okeechobee, Florida,
and assumed that they were after the eggs and young. Carr (1936)
was the first to report aggregations of cottonmouths on the islands
of the Cedar Keys group, where he found 11 of 13 captured snakes
coiled beneath nest trees. In May 1942 Mr. and Mrs. Allen D.
Cruickshank (pers. comm.), encountered a concentration of cotton-
mouths and banded water snakes, Natrix fasciata, under a heron and
glossy ibis rookery at King's Bar Reef, Lake Okeechobee, Florida,
where 3 to 10 cottonmouths swam in front of the blind constantly
during the week they were there. This couple also report seeing
from 8 to 12 of these snakes on 20 April 1942 in the vicinity of anhinga
and egret nests near the present Anhinga Trail in Everglades Na-
tional Park, Dade County, Florida. W. T. Neill (pers. comm.) found
cottonmouths very common under nests of about 95 little blue herons
at McKinney's Mill, a small bonnet-choked cypress pond in Emanuel
County, Georgia. Neill had noted that cottonmouths were not nor-




mally abundant there, and believes they came from other nearby
ponds, drawn by the odor of the fish and excreta. John N. Hamlet
(pers. comm.) saw many large cottonmouths in an active anhinga
and heron rookery near Pritchardville, South Carolina, from 1951 to
On the Florida mainland cottonmouths occur most commonly in
shallow ponds, marshes, and swamps. When water levels drop the
life concentrated in them provides a considerable food supply for the
cottonmouths. Allen and Swindell (1948) report cottonmouth ag-
gregations at pools left in drying marshes. Henry P. Bennett (pers.
comm.) encountered cottonmouth concentrations in 1955 in drying
sloughs and ponds in the Corkscrew Swamp sanctuary, Collier
County, Florida. When such ponds dry completely the cottonmouths
apparently seek out deeper ponds or subsist on dry land until the
water table rises again.
Walter Auffenberg (pers. comm.) collected reptiles from 1949 to
1951 between DeLand and New Smyrna, Volusia County, Florida.
He noted that when water levels fell, aggregations of cottonmouths
fed ravenously on the abundant life concentrated in the remaining
pools of roadside ditches, consuming fish, frogs, rodents, and reptiles.
Sometimes they ingested inanimate objects as well, for the stomachs
of two specimens dissected after death were packed with mud and
some with sticks up to 12 mm in diameter and 75 mm long. Burkett
(1966) remarks on the ingestion of plant material by midwestern
Sometimes cottonmouths move considerable distances. Hamilton
and Pollack (1955) record a cottonmouth killed 1 mile from the
nearest water at Fort Benning, Georgia. Probably such overland
journeys are aided by a keen olfactory sense. Noble and Clausen
(1936) have shown that the sense of smell is very important in some
snakes. Fish odor apparently attracts cottonmouths, for Neill (pers.
comm.) noted cottonmouths drawn to a fish-cleaning platform 50 m
from a lakeshore.
I conducted several tests to verify the cottonmouths' scenting
ability on Sea Horse Key. A crushed sardine and oil trail was ineffec-
tive in February. In early March 1967 near Gardner's Point I placed
a known number of pieces of cut mullet at points where no snakes
were present within a radius of 30 m. The next morning three pieces
were missing and I found two snakes in dense cover about 20 m
away; one, a male, contained one piece of mullet; the other, a female,
two. At another locality I caught two snakes, including a 356-mm
juvenile, in a small funnel trap baited with mullet.


Vol. 14



* AA












56 57

AND 1957

FIGURE 4. Location of nest trees on Sea Horse Key used by birds (principally
cormorants). Symbols show years occupied.










In early April I placed five piles of 10 chunks of mullet on the
ground at 2100 between Stations 95 and 115 and visited them re-
peatedly until 2300. A light breeze blew from the east. Shortly
after 2100 near Station 115, a snake was seen to eat one piece and
crawl away; another snake was discovered swallowing one piece 30
minutes later, and a third snake ate two pieces of fish 1 hour and 20
minutes later. As the last two individuals were spattered with avian
excreta, they were presumably drawn a minimum distance of 35 m
from the nearest nest tree. It is puzzling that the snakes ate only
one or two pieces of cut fish each instead of gorging themselves as
they might have.

Spring aggregations of cottonmouths beneath nest trees are com-
prised of individuals arriving from varying distances (Fig. 4). Thirty
snakes captured during the previous non-nesting period, 1 September-
28 February, and found beneath active nest trees had moved an aver-
age of 62 m. Only two had presumably arrived from distances ex-
ceeding 150 m., only five from over 100 m. During the rookery season
16 snakes did not move to a nest tree; the closest point of their ac-
tivity ranges to an active nest tree averaged 139 m. These data sug-
gest that Sea Horse Key cottonmouths are seldom lured by scent to a
nest tree further than 150 m.
Table 1 summarizes the distances between points of capture for
483 snakes and large annually active nest trees (six or more nests per
tree). Except for two osprey nests, all trees were cormorant rook-
eries. Two-thirds of the cottonmouths taken in the nesting season
were found within 32 m of an active nest tree, and evidently more
than half of the snakes remain with in 32 m of these trees during fall
and winter months.

Distance from nest tree Nesting Season Non-Nesting season
(in meters) April 1-August 31 Sept. 1-March 31
0- 16 42 56
17- 32 54 147
32-150 42 142
TOTAL 138 345

Of 402 original captures, 234 snakes were taken on the low penin-
sula during the nesting season (1 March-31 August). Of these 121


Vol. 14




I 0
a^ 0







0 0 0 0

o o


00 0

FIGURE 5. Midpoints of cottonmouth activity ranges on the low peninsula of
Sea Horse Key.



were taken under, or had been under (bore avian excreta) active
nests; 172 (73.5%) captures were within 32 m of the nest trees.
The midpoints of snake activity ranges (Fig. 5) plotted on a map
of the low peninsula show that the bulk of the population is concen-
trated between Stations 68 and 77 on the west side of the peninsula,
and from Station 92 west around the entire Gardner's Point area. A
60-m circle (mean distance moved) drawn around each active nest
tree excludes only 15 per cent of range midpoints; 8 per cent of the
range midpoints are more than 100 m from active nest trees. Evi-
dently most individuals live within the mean distance at which the
majority are attracted to nest trees.
Thus the location of rookery trees appears to control the distribu-
tion and food habits of almost three-fourths of the Sea Horse Key
cottonmouths. With the snakes so dependent on the birds, obviously
their nesting habits must effect the welfare of the cottonmouth popu-
Well developed olfaction is one facet of a generalized behavior
pattern enabling cottonmouths to adapt to the environment of Sea
Horse Key. Were it not for their ability to locate the principle food
sources of the island from a considerable distance, these snakes would
doubtless be far less abundant, and the density (22.27 per acre)
would more nearly approach that of the main ridge (1.85 per acre).
On the ridge the reptiles apparently feed chiefly on rodents.
During hot summer days cottonmouths are seldom found in the
open rookery areas. At these times they remain tightly coiled in the
nearest heavy cover, crawling to the nest trees at dusk. Of 232 night
captures, 141 were taken under active nest trees, 47 in 1955, 42 in
1956, 52 in 1957, distributed monthly as follows: March 2, April 26,
May 43, June 55, July 2. This coincides roughly with the availability
of dropped fish.
I have watched 17 different snakes in the act of feeding on fish
or fish remains. During April 1955 and May 1956 snakes aggregated
under the nest trees about 15 minutes after dark, gliding about,
searching and feeding. I have seen their reactions to dropped fish
several times. A falling fish instantly alerts them. With the head
raised about 125 mm they glide quickly near to where the fish landed,
then lower the head and try to locate it, apparently by use of the
tongue. The snakes generally find and swallow a fish within 5 to 10
minutes after it falls.
While feeding beneath nest trees cottonmouths are quite active
and easily disturbed by the flashlight beam, moving quickly for the
nearest cover. By working carefully it is possible to move among a


Vol. 14


feeding aggregation, and I have captured as many as 9 individuals
beneath a single tree. When beneath active nest trees the snakes
are quick to investigate any commotion in the leaves. Sometimes
they may be lured by throwing sticks or other objects to simulate fall-
ing fish. I once tapped my catch stick on the ground and a snake
came forward with upraised head and struck at it.
Young cormorants occasionally fall to the ground. Fallen fledg-
lings I placed near searching cottonmouths were never eaten, though
I once found a snake that had swallowed a cormorant leg and another
that had ingested a wing, both probably scavenged from a decaying
carcass. The remains of many well feathered nestlings are found
on the ground where it is apparently difficult or impossible for parent
cormorants to feed their young. Carr (1936) reports a portion of an
eggshell in a cottonmouth on Snake Key. It is extremely rare to find
an unbroken egg on the ground. Fallen nestlings and eggs are un-
doubtedly insignificant food sources.
The small size of some dropped fish does not deter feeding cotton-
mouths. Carr (1936) found several tiny fish in a sizable cottonmouth
from Snake Key. I once saw a 1422-mm male swallow two fish 50
mm long.
Small cottonmouths may attempt to swallow fish heavier than
themselves. I found a 711-mm snake weighing 269 grams attempting
to swallow a 305-mm, 354-gram serranid dropped by an osprey. Some-
times parts of fish skeletons are eaten. One small cottonmouth had
about 25 mm of the skull of a catfish, Bagre marinus, protruding from
its body about 100 mm behind the head. A 559-mm male was seen
eating the skull of another fish.
Large cottonmouths sometimes eat small and unusual prey. Carr
(1936) reported that a 1473-mm specimen from Snake Key had eaten
a skink. A 1016-mm specimen from Snake Key that I took had eaten
a caterpillar and a 1295-mm snake from North Key had eaten a ter-
restrial snail about 3 inches long. Burkett (1966) notes that cotton-
mouths feed on both insects and gastropods. Cottonmouths are oc-
casionally ophiophagous. In the fall of 1955 I saw two water snakes
(Natrix sipedon ssp.) at Station 160, at Gardner's Point and caught
one; a few days later I took a cottonmouth containing a Natrix from
the same area.
Cottonmouths may compete for food under nest trees. Two snakes
were once found engaged in a violent tug-of-war over a 125-mm dog-
fish, (Opsanus sp.). On another occasion I found two large male
snakes, both over 1270 mm, struggling over a fledgling crow.
Small cottonmouths are uncommon beneath nest trees and no




newborn snakes were found there. Of 101 original captures taken
beneath these trees, only 4 snakes were under 610 mm, and all con-
tained fish or were feeding when captured; 22 others ranged between
610 and 914 mm, 64 between 914 and 1219 mm, and 11 above 1219
I think that undisturbed snakes must return to the same nest trees
repeatedly, but my experience suggests that snakes may leave tempo-
rarily the vicinity of capture, very likely because of the shock of the
experience. Both males and females sometimes make a "shock" or
escape run following release. In 9 instances this straight line escape
behavior of large male snakes carried them out into salt water for
about 30 m before each turned back to shore; I never saw a female
enter the sea. On 6 June I captured 4 snakes at Station 92; on the
following night I found 5 different individuals there. I believe that
my handling of the previous night caused the first 4 snakes to leave the
immediate area of the tree
Normally snakes wait for darkness to move into exposed places
under isolated nest trees, although on hot July days they begin to
gather beneath egret and night heron nests in dense canopy by 1700.
Occasionally they feed under nests in the daytime. On 5 April I
watched a 1041-mm female crawl several meters to a dropped fish at
1400. During daylight hours I once slid a white 6-foot carpenter's
rule through the leaves to within 250 mm of a large male snake, which
struck it viciously, perhaps a feeding reaction.
After young cormorants leave the nest tree, they frequently return
to it to be fed by the parents. In late July I took 8 snakes scavenging
at night at Station 120 where young cormorants still perched in their
nest trees. Later (mid-July to early September), these cormorants
leave their nest tree and congregate in certain roost trees. The
snakes seem to leave the nest tree as soon as the cormorants depart.
On 27 June I noted snakes beneath the Station 91 cormorant nest tree
(still occupied by young birds), whereas the Station 86 nest tree had
neither birds or snakes. By 19 July only a few snakes remained in
the area of the nest trees, but I caught two under new roosting trees.
While ospreys are not plentiful enough on Sea Horse Key to be
principal provisioners for snakes living there, they are important as
they start carrying fish before other birds begin nesting. On Snake
Key 24 February, I collected a 350-mm, 681-g mullet one of a pair of
ospreys dropped. Courtship maneuvers of ospreys often involve
carrying fish, which are sometimes dropped from the feeding perch.
One night a perched osprey dropped a 681-g serranid at Station
110, indicating they may go to roost holding a fish. Most osprey-


Vol. 14


caught fish were either trout, Cynoscion sp., serranids, or mullet,
Mugil sp. and large enough for a substantial meal. On Snake Key, as
on Sea Horse Key, cormorants provide most of the food. Herons
and egrets are minor contributors. Ibises, because they feed on small
crabs and crayfish, probably contribute little. In 1966 and 1968 a
large rookery of white ibis occupied most of the main ridge of Sea
Horse, but no increase of cottonmouths was noted beneath the nests
while at the same time snakes were markedly numerous beneath
small rookeries of the brown pelican, Pelecanus occidentalis, a species
that had not nested on the island during the initial study.
To ascertain how long individual snakes attended nest trees in
consecutive years, 218 captures from Sea Horse Key were plotted by
year, month, and capture point. Of 3 individuals captured during 3
consecutive feeding seasons, 1 was taken at the same tree each
year and 2 had moved to other trees. Of 15 snakes captured in 2
successive feeding seasons, 7 returned to the same nest trees. Of the
other 8, 3 left probably because nesting stopped in the old tree, 4
changed to other nest trees (about 50 m away) even though the
original tree was still active, and 1 moved 190 m for no apparent
Station 76 functioned as an active nest tree for 3 consecutive
years. Four snakes taken there in the winter of 1954-55 were found
there again in the summer of 1955, 1 remained until the winter of
1955-56, and 2 until the summer of 1956. Of 3 more taken initially
in the summer of 1955, 3 remained through the following winter, 2
persisted until the summer of 1956, and 1 stayed for the winter of
1956-57. During the same 3 years 16 snakes arrived from other nest
trees. The small size of activity ranges seems to preclude a con-
tinuous nomadic wandering from tree to tree, although the cotton-
mouths usually move widely enough to include several active nest
trees within their activity ranges.
I conclude that while some snakes may remain at or near a nest
tree for 3 consecutive years, the bulk of the population seems divided
between those individuals that remain about 2 years at a nest tree
and those that move to another site. If disturbance by crows and
ospreys should make cormorants regurgitate heavily in a certain area,
or if younger birds drop fish more often in certain trees, snakes
might be drawn by scent from one nest tree to another. Also a snake
on its escape run after the traumatic experience of being handled
may approach within smelling range of a different rookery tree.
Fish dropped by birds provide a continuous source of food through
the warmer months when reptile metabolism is highest. I believe




the very small number of cottonmouths I encountered on several
trips to both Atsena Otie and North Keys can be explained by the
absence of large rookeries. Rats and the few fish dropped by the 6
or 8 pairs of ospreys seem to constitute the only food for the cotton-
mouths on Atsena Otie.
As the welfare of most cottonmouths on Sea Horse and Snake Keys
is dependent on the rookeries, the snake population has undoubtedly
fluctuated over the years, along with the nesting bird populations.
The interrelationship is not entirely one-sided. The legend that the
islands swarm with venomous snakes normally protects the rookeries
from invasion by man. The presence of snakes near nest trees may
also discourage the roof rats that might otherwise prey upon the eggs
and nestlings. In 1958, unfortunately, an estimated 400 snakes were
removed for venom research at the University of Florida Medical


As cottonmouths on the Florida mainland are chiefly found in
aquatic habitats where their normal sphere of activity is influenced
by a body of fresh water, it is interesting to examine the movements
of cottonmouths in the terrestrial, insular surroundings of Sea Horse
Key. Whether they wander at random or favor a circumscribed area
has an important bearing on the ability of this limited environment
to support a large number of reptiles. Activity range and movement
was studied by plotting points where each snake was captured. Pro-
vided they were captured more than twice, the area enclosed by
lines connecting these points is regarded as an activity range as de-
fined by Carpenter (1952).
The activity ranges established in this study are based on marked
and recaptured snakes. Individuals were marked and released at the
point of capture. Of these 107 were captured 3 or more times, pro-
viding usable (three-dimensional) data. Six snakes were taken 5 to
6 times each, six 7 times, and two 8 times. The mean number of cap-
tures, including the initial capture, was 3.8 per snake, and the mean
elapsed time between initial capture and the last recapture for each
of 107 snakes was 18.6 months. Thirty-five snakes were taken 2
years or more after the initial capture, and one was retaken after 39
Capture-points were plotted on scale maps of the island using
compass bearings from the nearest station and station to snake dis-
tances. Straight lines connecting the outermost points of capture


Vol. 14


were then drawn on the map. The areas of these triangles and poly-
gons were measured in acres with a planimeter.
Activity ranges for Sea Horse Key cottonmouths vary from less
than 0.11 acre to more than 3 acres. Males seem to have slightly
larger ranges than females (M 31 =0.43 acre, M 58 9 =0.35
Over 18 per cent (15 9, 5 S $ ) have activity range of less than
0.11 acre. With two exceptions these captures spanned a 7 to 33-
month period. Four snakes remained in almost the identical spot
for well over 2 years. Small activity ranges were often associated
with the presence of nearby winter dens and food, sources; half of
20 snakes with limited range lived very near both a den and a food
source (usually a rookery tree). Others were reasonably near a den
and about 50 meters from a possible food source. Only one snake was
not near a den or a food source.
In 16.8% (n=18) the activity range is greater than one acre; 16
of these were excluded from the calculation of mean range, for most
of these longer movements could be accounted for by travels, pre-
sumably to wintering areas. Six of the ranges were greatly extended
by travel to large palmetto patches, while five of these movements
were by snakes that wintered on the wind-shielded east side of the
low peninsula with its thicker vegetation. One large male was cap-
tured 2 successive summers at the nest tree of Station 76; each year
it traveled 295 meters to a wintering area near Station 34. Three
other large activity ranges can be explained by the abandonment of
Station 92 as a nesting site. Any cessation of nesting at a given site
may also cause permanent changes of range.
An example of the complete desertion of a rookery and its effect
on the cottonmouths is afforded by the area near Station 36. John
D. Kilby (pers. comm.) recalls that around 1934 a large rookery of
white wading birds occupied this vicinity. In 1954 the cherry-laurel
and bay trees contained old nests probably used for the last time in
1953. During the 3 years following 1954 snakes became progressively
less numerous in the vicinity; seven emigrations were noted. It seems
reasonable to suppose that the abandonment of the rookery caused
these snakes to leave. Most evidently migrated to active nest trees
elsewhere; several skeletons attested the fact that some died. The
number of individuals remaining approximated that of the normal
ridge population where no birds nest.
As the main ridge supports far fewer snakes than the rookery-
bearing peninsula, the size of the activity ranges in both habitats
might be compared. Only two snakes from the main ridge were




captured three times; one had a range of 0.40 acre, the other 0.11
acre. Ten additional snakes from the main ridge were captured only
twice. By measuring the distance between the capture points of

.0 .W .

0 50

*A \Y
iI 7 4.
IC I 4 \ / ^.4



N %

P -]:I




these and a sample of 33 from the peninsula, rough comparisons can
be made. The mean distance between capture points for the ridge
snakes was 60 m; the peninsular snakes, 71 m. The average number
of months covered by the ridge captures was 9.8; for the peninsular
snakes, 12.8. If one may draw a conclusion from only 12 captures,
the ridge-inhabiting snakes apparently have activity ranges of ap-
proximately the same area as those of snakes in the low peninsula.
Figure 6 plots the activity ranges of 16 cottonmouths on Sea Horse
Key and shows their proximity to active nest trees, dens, and winter-
ing areas such as saw palmetto patches. The activity ranges B, M,
N, and 0, are noteworthy for their extremely small size; the snakes
apparently remained in a tiny area for nearly 3 years. The activity
range of N shows initial escape behavior to point R following capture
and exact homing return, a common occurrence among large male
snakes. Specimen A illustrates usual behavior; in February 1955 this
snake was taken in a den, but spent the next 2 winters in the Palmetto
patch at Station 95; in the summer of 1956 it was taken under a
nesting tree at Station 92, and it returned to this vicinity in the
spring of 1957 though the tree was inactive. Specimens G and F
wintered in nearby palmetto patches. Snake Q wintered in the deep
leaves about several hickory trees at Station 32. One of these trees
formerly had an osprey nest, but it was not in use, and the snake then
journeyed to the active osprey nest at Station 107, where it was taken
As stated above, movement to a wintering area greatly increases
areal range. Snake 121 fed in the area between Stations 88 and 115
but wintered in the palmettos at Station 95, a movement of 160
meters. Snake 269 wintered in 1955 and 1958 at Station 95, then
moved 180 meters to feed at the nest trees of Station 76. Snake 323,
originally captured at Station 92, apparently traveled to winter in the
palmettos at Station 107, a distance of 300 meters.

FIGURE 6. Activity ranges of 16 cottonmouths on the low peninsula of Sea
Horse Key. I, captures under active nest trees; II, captures at or
near dens or wintering areas. Each point indicates a single capture.
The data below are arranged in the following sequence: Letter
designating home range, snake number, sex, activity range in acres
(in parenthesis), and number of months over which range was de-
termined. A 26 9 (0.66) 25; B 42 9 (0.11) 34; C 28 9 (0.55)
27; D 261 9 (0.66) 7; E 171 9 (0.22) 19; F 17 $ (0.22) 25;
G 280 9 (0.24) 27; H 78 9 (0.40) 22; J 8 $ (0.77) 18; K 227 9
(0.15) 29; L 212 9 (0.16) 30; M 135 9 (0.10) 13; N 293 $
(0.11) 10; O 2349 (0.11) 29; P 76 S (0.11) 27; Q 87 9 (0.22)
19; Point R is discussed in the text.



Six snakes showed remarkably long movements, which I can not
explain. A 1321-mm male, number 50, traveled 320 meters from
Station 103 to Station 120 in 27 months. A 635-mm female, number
161, traveled 380 meters in 6 months. Female 270 traveled 450
meters from Station 34 to Station 124 across (or around) the man-
grove inlet, and female 332 in 4 months traveled 498 meters from
Station 32 to Station 116. Female 237 is unique in ranging for at
least 8 months on one side of the mangrove inlet at Station 129, then
crossing or circumnavigating the mangroves to establish a new range
on the other side.
More remarkably a 1448-mm male, number 238, not only ventured
from Gardner's Point to the vicinity of the laboratory on the main
ridge, but did it twice, perhaps illustrating a homing tendency. First
captured in October 1955 at Station 125, it was taken 12 months later
by Doyle Folks at the boat landing; 830 m distant. In July 1957, 11
months later, the snake was retaken 60 m from its original point
of capture 2 years before. In February 1958 I was astounded to en-
counter this snake again coiled near the dock, having in 8 months
made its way back 732 m to the vicinity of the laboratory.
A large bi-directional snake trap with drift fences 2 feet high was
installed across the entire island from shore to shore at Station 16.
No appreciable movement of snakes was noted, for the trap appar-
ently took only those individuals within whose activity range it was
Klauber (1956) reviewed marking and recapture studies on
crotalid snakes. Fitch (1949) concluded that the Pacific rattlesnake,
Crotalus viridis oreganus, shows no evidence of a home base and that
the ranges of males might be as large as nearly 30 acres, females 16
acres. Fitch (1960) calculated the home range for Agkistrodon
mokeson males to be 24.4 acres, for females 8.5 acres. Carpenter
(1952) found that garter and ribbon snakes, Thamnophis sp., have a
tendency to remain in a limited area, and he recaptured 42 that had
moved an average distance of 81 meters, 85 that moved an average
distance of 60 meters. These distances approximate distances moved
by cottonmouths at Sea Horse Key. Carpenter gives the maximum
activity ranges of Thamnophis s. sirtalis as 4.15 acres, the average as
2.07 acres. The average Sea Horse Key cottonmouth has an activity
range of less than half an acre, limited indeed, compared to Agkistro-
don mokeson, Crotalus, and Thamnophis. This may be partly due to
the birds that bring them food and because rats and lizards are abun-
dant in this environment. I strongly suspect that when food is plenti-
ful cottonmouths are quite sedentary.


Vol. 14



The activity ranges of Sea Horse Key cottonmouths are not littoral,
nor do they provide an access corridor to the sea. Thus salt water is
apparently not a significant factor in their lives. Their ranges for the
most part are inland, and their small size enables the low peninsula
to support a high population of snakes in a limited area. Snakes do
not gather at the trees where nesting begins, but tend to be at-
tracted to the nest tree nearest their range. Thus the available food
supply is apportioned more evenly among the total population.
The close proximity of large male cottonmouths may precipitate
combat. One actual fight I watched occurred in foxtail grass (Chae-
tochloa macrosperma) in the rookery area of Gardner's Point, at 2230
on 24 June 1956 between two males that measured 1333 mm (2098g)
and 1384 mm (1489g). The participants at first eyed each other,
heads held 15 cm high, then hooked necks and threw each other to
the ground. Combat ended 4 minutes later when one snake suddenly
glided directly toward me while the other traveled 2 meters in the
opposite direction. The thinner but longer snake was unharmed; its
opponent had been bitten in the side at mid-length. A moist, slightly
swollen spot was oozing blood, otherwise the snake behaved normally.
Possibly I interrupted a battle on 6 April 1957 when I found 2 males
of equal size lying across each other, with a female within 0.75 meters.
All 3 crawled off after 5 minutes, probably disturbed by my approach.
Jousts between males are a remarkable characteristic of North
American crotalids. Ramsey (1948) noted them in Agkistrodon pis-
civorous leucostoma, and Allen and Swindell (1948) watched a
"dance" between two captive 4-foot moccasins of the eastern sub-
species in September that lasted 4 hours. Shaw (1948) describes
the combat dance in the copperhead Agkistrodon mokasen laticinctus.
Lowe (1948) states that the dance of male North American crotalids,
which he calls territorial fights, occurs in both fall and spring in
captivity and in the field, and that biting during them is rare.
The first instance of combat (above) on Sea Horse Key seems
late in the year to be associated with mating. No female was found
nearby. Territoriality is an unsatisfactory explanation when snakes
aggregate in rookery areas. This particular fight may have been ini-
tiated by an accidental bite. The absence of bites on other cotton-
mouths seems to support this assumption.

If one generalization can be applied to the cottonmouth, it is that
this snake apparently eats whatever animal food is available, from a



decomposing frog in a roadside ditch to a full-grown American egret.
This is undoubtedly a highly important factor in allowing the cotton-
mouth to survive in an island environment such as Sea Horse Key.
Burkett (1966) lists food he examined from 46 cottonmouths
from Arkansas, Louisiana, and Texas and summarizes food reported
by 17 other authors. Other lists of foods eaten by the adult cotton-
mouth may be found in Strecker (1926), Alien and Neill (1950), and
Wood (1954). In the stomachs of 20 specimens taken in Louisiana
Amy (1948) found mammals in 5, reptiles in 9, a caterpillar in 1,
and unidentifiable masses in 7.
Schwartz (1952) reports that in the Florida Keys a 12-inch speci-
men had eaten a shrew, Blarina brevicauda, and a rice rat Oryzomys
palustris, while a 41/-foot snake had consumed a half-grown marsh
rabbit, Sylvilagus palustris. O'Neil (1949) lists the cottonmouth as
seventh ranking predator on the muskrat in Louisiana coastal marshes.
Parker (1937) records a juvenile containing a skink, Eumeces fascia-
tus. Peterson, Garrett, and Lantz (1952) captured two cottonmouths
on Key Vaca, Monroe County, Florida that in company with several
Natrix sipedon compressicauda, were apparently feeding on a brackish
water breeding aggregation of the giant tree frog, Hyla septentrionalis.
Birds and bird eggs are reported eaten by cottonmouths less often
than mammals and reptiles. Adams (1955) reported cottonmouths
in Louisiana eating a sora rail, Porzena carolina, and a seaside sparrow,
Amnospiza maritime. Leavitt (1956) noted a Pied-billed Grebe,
Podilymbus podiceps, eaten in the Gulf Hammock area of Florida.
Mrs. Allen D. Cruickshank (pers. comm.) reports that at King's Bar
Reef, Lake Okeechobee, the cottonmouth swallows the eggs of ibis
and other birds whole with the shell intact; in May 1942 she killed a
2803-mm specimen there that contained a glossy ibis egg, three Loui-
siana heron eggs, a full-grown immature American egret, and an
adult glossy ibis. She also noted that when cottonmouths approached
the nests, the ibises leaned over and struck at them; a number of dead
birds found with peculiar blood clots about the head suggested the
snakes may have struck back.
Rhea Warren, who has collected cottonmouths in the Everglades
for 12 years, told me (pers. comm.) that on a half dozen occasions
he has seen these snakes at night scavenging snakes and frogs killed
by automobiles on the black-top pavement of the Tamiami Trail west
of Miami. That cottonmouths readily feed on other snakes is well
established. A number of authors, Conant (1934), Penn (1943),
Allen and Swindell (1948), Smith and List (1955), and Burkett
(1966) have reported cottonmouths eating their own kind, both


Vol. 14



Food Items Number Snakes


Roof rat, Rattus rattus 24
Gray squirrel, Sciurus carolinensis 4


Mourning dove, Zenaidura macroura 1
Fish crow (fledgling), Corvus ossifragus 1
Towhee, Pipilo erythrophthalmus 1
Cormorant (parts), Phalacrocorax auritus 3
Unidentified small birds 2


Little brown skink, Lygosoma laterale 1
Florida five-lined skink, Eumeces inexpectatus 4
Anole, Anolis carolinensis 1
Salt water snake, Natrix sipedon 1
Marine Fish' 48


Caterpillar (unidentified) 1
Spider (unidentified) 1
Carapaces of spider crab1 2
Remains of shrimp1 2


Carnivorous land snail, En iJldiJa rosacea 1
Conch (unidentified)' 1


Chicken and turtle bones (discarded refuse) 1

'Dropped by nesting birds

young and adult. If Sea Horse Key snakes are indeed at a subopti-
mum food level, it is surprising that no instance of cannibalism was
observed during this study.
The only previous information on the food of the Cedar Key cot-






Month Food Mass Number of Per cent
Identified Unidentified1 snakes examined with
Jan. 2R, 2S 2 71 8.4
Feb. 1B, IF 0 78 2.5
Mar. 1B, 1E, 7F, 5R 7 108 18.5
Apr. 11F, 2SH, 1R, 1S 6 115 18.2
May 7F, 1R 10 62 29.0
June 2B, 2CO, 2F, 1R
1SC 12 77 25.9
July 1CH, 1CO, 1E, 11F
1R, 1S 2 81 22.2
Aug. 1A, 1C, 1E, 4F
1R 0 26 30.7
Sept. 3 125 2.4
Oct. IF 3 57 7.0
Nov. 1B, 2F, 1L, IN
3R 0 46 17.3
Dec. 1CR, IE, 4R 1 86 8.1

Key: A-Anolis, B-Small Bird, C-Crab, CH-Conch, CR-Caterpillar, CO-Cormorant
(Body parts only), E-Eumeces, F-Fish, L-Lygosoma, N-Natrix, R-Rat,
S-Squirrel, SH-Shrimp, SC-Refuse.
1Probably fish

tonmouths is by Carr (1936), who found food remains in the stomachs
of 6 of 13 moccasins from Snake Key. Two of these contained skinks,
Eumeces inexpectatus, two had ingested heron feathers (probably
accidentally), and two contained bird bones of a single limb. Carr
discussed the food sources available to the Snake Key cottonmouths
and concluded that neither the heron rookery, reptiles present, nor
the salt water fish offered adequate nourishment.
The majority (89.5 per cent) of the stomachs of Sea Horse Key
cottonmouths I examined were empty, which suggests that the island
snakes feed less frequently than those on the mainland. Barbour
(1956) found that 25 per cent of the cottonmouths in a Kentucky
pond contained food. Hamilton and Pollack (1955) found food in all


Vol. 14




Original captures
Number % with food

Number % with food

Jan 29 10 42 7
Feb. 43 2 35 0
Mar. 52 21 56 16
Apr. 56 31 59 8
May 31 29 31 23
June 31 39 46 8
July 35 17 46 5
Aug. 11 18 15 0
Sept. 62 5 63 0
Oct. 29 7 28 4


Dec. 39 12 47 2

9 of the snakes they examined in Georgia. Arny (1948) found food
in all of the 20 specimens he captured in Louisiana.
Table 2 lists food eaten by 93 individual cottonmouths from the
Cedar Keys area. Table 3 lists this food by month, with the per-
centages of snakes containing food. As most palpable, but unidenti-
fied, food masses listed in Table 3 occur during the rookery period in
May and June, they probably represent fish. If a snake contained
what I felt was other than fish, I either gently made it regurgitate, or
else killed and dissected it.
Table 4 shows that the snakes are more likely to contain food
when captured for the first time than when recaptured (original cap-
tures with food, averaged 16.8 per cent; recaptures with food, 6.7
per cent). This seems to be additional evidence that the initial
capture of a crotalid snake produces a profound and lasting effect
on the snake. This phenomenon was first reported by Fitch and
Glading (1947) in Pacific rattlesnakes. Fitch (1949) found that all
his California crotalids lost weight up to 29 months. I showed previ-
ously (Whartbn, 1966) that the 47 Cedar Key cottonmouths with
good weight data over a 3-year period lost an average of 86.5 g yearly.
When it is considered that most of these snakes were captured gently,



measured, weighed, and released within 5 minutes, this remarkable
reaction is difficult to explain.
The two fish the Sea Horse Key cormorants feed on most often are
pinfish, Lagodon rhomboides, and Gulf toadfish, Opsanus beta. I
have seen the snakes eating both. I once found a cottonmouth in the
act of eating a spiny boxfish, Chilomycterus schoepfi. Between April
and September, I collected the following other fish disgorged by
cormorants: cod, Uroplycis floridanus, majarra, Encinostomus sp.;
leatherfish, Monocalithus ciliatus; and whipsnake eel, Bascanichthys
scuticaris. I have never seen a mullet, Mugil sp., or trout, Cynoscion
sp., disgorged by cormorants, despite contrary statements by local
Ospreys are the source of trout, mullet, and grouper, Mycteroperca
sp., in the cottonmouths' diet before 20 March. I have 8 records of
fish consumption between 28 October and 19 March that are probably
osprey drops. Between the desertion of rookeries and perch trees in
August and the start of nesting in March (Table 3), food intake drops
markedly and is principally confined to reptiles and mammals. Rats
apparently provide the bulk of nourishment during this period; they
probably fall prey to the cottonmouth when searching for acorns in
the ground litter in November and December though squirrels,
thrashers, towhees, and thrushes are also very active on the ground.
The presence of rats in snake stomachs in March suggests that at this
time the rats are also feeding on dropped fish scraps in competition
with the earliest cottonmouths to visit the nesting areas.
While skinks are eaten only occasionally by adult snakes, they
may be the principal food of young cottonmouths in the Cedar Keys.
Of the 5 skinks recorded, 2 were from snakes less than 356 mm. The
largest snake that had eaten a lizard was 940 mm. One 483 mm
young snake contained the primary feathers of a small warbler; 2
others less than 350 mm in length contained bits of shrimp regurgi-
tated by birds. It must be difficult for a small snake to find regurgi-
tated particles small enough to swallow beneath the nest trees. Of
48 snakes found eating food dropped by birds, only 7 measured less
than 600 mm, and the mean length of 30 scavenging cottonmouths
was 962 mm. Both food particle size and competition from larger
snakes probably limit the scavenging activities of the smaller snakes.
Rats appear to be too large for snakes of less than 600 mm to
swallow. The smallest snake to have eaten a rodent was a 508 mm
specimen that ate two 23 g young rats in December. A 660 mm
snake ate two young rats weighing 42 g each. The mean length of


Vol. 14


the snakes that had eaten rats was 1046 mm. The four squirrels
(Table 3) were taken by snakes over 1200 mm.
Evidently rookery scavenging is about the only source of food
for snakes on Snake Key. Rats and other small mammals are either
absent or quite rare; I found none in the 88 snakes I examined from
this island, nor did I trap any. This absence of mammalian food
does not seem to effect the population adversely, for it seems healthier
than the one on Sea Horse Key (Wharton, 1966).
Both North and Atsena Otie islands lack communal bird rookeries
and rats probably constitute the cottonmouths' major food source.
Although 3 of 4 snakes from North Key were taken beneath osprey
nests, from the incidence of parasitism by Porochephalus crotali in
these snakes and bait pilfering, I believe the low snake population
there exists primarily on rats. I trapped rats on Atsena Otie, found
the same high incidence of parasitism, and concluded that rats are the
major food on this island as well.


Hibernation and aestivation are common reptilian behavioral
responses to temperature extremes. Strecker (1926), Gloyd (1938),
Cagle (1942), Arny (1948), Dundee and Burger (1948), and Burkett
(1966) have reported on the denning habits of the western cotton-
mouth, A. p. leucostoma. Dundee and Burger found them 1/2 mile
from and 36 m above the nearest permanent water. Strecker found
them in rotten logs, Dundee and Burger in limestone cliffs, and
Gloyd in rock crevices. Neill (1948) found A. p. piscivorus in de-
caying stumps. Alexander Sprunt, Jr. (pers. comm.) poked 15 out
of a stump near a cypress swamp on an Edisto River plantation in
South Carolina. Neill (1947) suggests the cottonmouth is more
cold-tolerant than most snakes in the Richmond County, Georgia
area and says it is one of the last to hibernate.
Sea Horse Key cottonmouths seek temporary winter shelter.
Specimens have been noted away from dens during warm spells of
every month of the year. Numbers found hibernating over the 3-
year period are: 4 in November; 16 in December; 25 in January; 10
in February; 1 in March.
While palmetto patches are frequently used, the principal under-
ground refuges were the stump holes of trees blown over in the 1950
hurricane. These trees all lie in the same direction, their trunks
aligned almost north-south. The holes are generally shallow, less than
300 mm deep, and the occupants can be located by flashlight. I







\ S*




FIGURE 7. Subsurface winter dens and wintering areas (palmetto) of Sea Horse
Key cottonmouths on the low peninsula. Solid symbol, occupied
dens; open symbol, unoccupied dens. Compare with Fig. 8.




Vol. 14

vdw, ,m*



have taken as many as nine from a single den (at station 153 in
January 1956), but the usual number is from one to five. Many of
these holes seem to provide scant protection, but little is needed
against the mild Gulf Coast winters.
Figure 7 maps 30 known active stump-hole dens on the low
peninsula and 9 probable ones, most of them around the periphery
of Gardner's Point and the western edge of the low peninsula. Snakes
also definitely winter in, and travel to and from, areas of thick
ground cover such as saw palmetto clumps and thick vines. The
grouping of marks on Figure 8 at the Station 95 palmetto patch
show the frequency of snakes encountered there between 15 December
and 28 February. I worked this patch more extensively than any
other and am convinced that it is actively sought in cold weather.
Here on 11 January 1956 I kicked out from under dead fronds two
males (1134 g each) with cloacal temperatures of 8.00C while the air
temperature was 7.0C. I believe that some snakes also winter be-
neath fronds in the low cabbage palm hammock.
One favored winter refuge is the dense growth north of Station
76, with much saw palmetto and heavy leaf mold; another is along
the south shore of the sheltered and sunny mangrove inlet. Other
denning places include deep accumulations of leaf litter around the
bases of trees, the interior of hollow logs, and the stump holes from
rotted cabbage palms. I found only two holes of the gopher tortoise
(Gopherus polyphemus) on Sea Horse; cottonmouths used one as
a winter den.
Temperatures at Sea Horse Key are seldom low enough to be fatal.
While denning may not be necessary to protect the snakes from ex-
treme cold, the practice is nevertheless important. Normally most
snakes den deep beneath ground level during winter and place mini-
mum energy demands on their metabolism. Selection of shallow
holes and emergence during winter warm periods by Sea Horse cot-
tonmouths make increased demands on energy reserves. This can
be fatal, as winter food is limited.
The earliest I found a snake in a den on Sea Horse Key was 6
November. Its cloacal temperature was 19.00C, the air was 17.00C,
and I feel that this snake was not hibernating, but either hunting or
seeking cover in the den. Normally snakes do not seek dens before
mid-December, and 90 per cent of snakes in dens were taken in
December, January, and February, the latter month having over 44
per cent of the winter total. Only one denned snake is recorded
for March. The latest I have found a snake in an underground refuge




0 50



0 1

0 \


oo *0 00
0 0

FIGURE 8. Location of 163 cottonmouths captured in fall and winter. Solid
symbols, captures 1 Sept.-30 Nov.; open symbols, captures 1 Dec.-
28 Feb. Compare with Fig. 7.



Vol. 14




was 7 April, with a cloacal temperature of 15.80C. The highest air
temperature recorded during denning was 18.30C.
On 18 and 19 December 1955 (air temp. 15.6C.) I took nine
snakes from seven sub-surface dens and one from a palmetto patch.
Their cloacal temperatures varied from 13.5 to 16.50C (M=14.90C).
Three snakes taken near Station 92 on 12 February 1955, had a mean
cloacal temperature of 4.20C (air, 5.6C), the lowest cloacal temper-
atures I recorded. These snakes were in a shallow den, and their
temperature was lagging well behind that of the air. The cloacal
temperatures of nine snakes taken in a den near Station 153 on 10
January 1956 were within 1.20C (M=10.70C) of each other at a soil
temperature of 12.80C and an outside air temperature of 7.8C. The
low of the previous night was 5.00C, and the highest daytime temper-
ature was 8.90C. Air temperature within the den was 9.10C at the
time of capture. This suggests that, in this instance, soil temperature
kept the snakes at a point about intermediate between soil and air


Temperature Humidity
Air Soil
Date and den number Den Surface Surface Den Surface
(4" depth)

18 Dec. 1955, Den 3 13.3 16.7 -85 70
19 Dec. 1955, Den 3 15.6 17.8 15.0 87 75
10 Jan. 1956, Den 13 9.1 7.8 12.8 -
11 Jan. 1956, Den 13 8.9 6.9 12.8 73 68
18 Feb. 1956, Den 3 18.9 21.1 19.5 96 92
4 Mar. 1956, Den 3 17.8 20.0 18.3 90 84
19 Jan. 1957, Den 7 11.3 13.3 12.8 -

Table 5 comparing temperature and humidity at ground level
and within different dens shows in five of the seven recordings the
den was from 1.3' to 3.40C colder than the outside air. The den air
temperature is usually closer to that of the soil. When air tempera-
tures drop the den remains warmer because of the lag of the soil
temperatures (10, 11 January 1956). As table 5 shows, den tempera-




tures usually remain colder when air temperatures rise. Dens also
have a consistently higher humidity than the surface air. Thus while
dens are only shallow, open stump holes, they are deep enough to
ameliorate temperatures and maintain a higher humidity. As Bene-
dict (1932) indicates, reptiles may lose heat readily by vaporization
of water; higher humidities in dens would tend to favor the conserva-
tion of heat.
On 11 December 1955 I found five snakes in a cedar stump-hole
near Station 128, which was open and scarcely below ground level.
Three snakes were coiled on one another deep in the den, and two
towards the entrance. The two outer snakes had cloacal tempera-
tures of 10.0C, the same as air temperature. The inner three were
distinctly warmer, with cloacal temperatures from top to bottom of
11.00C, 11.30C, and with the snake next to the soil 12.2'C.
One of the most perplexing wintering problems is den desertion.
Of 50 snakes taken in dens, only three were ever retaken again in a
den and none of these in the den in which it was originally found,
although each snake was released quickly into the opening of its den
after weighing. Near Station 92, an area that always yielded a
large number of snakes, there were several active nest trees in 1955
and at least one functional nest tree in 1956. In the winter of 1955 I
took 10 snakes from three dens near Station 92 and released them
near the same dens. They did not return to these dens that winter,
and the dens remained deserted the next 2 years. I found two of the
snakes in 1956 in a nearby den that had escaped my notice in 1955.
This den contained nine snakes in all, which I released at the den
mouth; none returned either that winter or the next, although two
new snakes appeared there in 1957. Not only were the Station 92
dens deserted, but in 1955 I took snakes from 10 other dens, 8 of
which remained deserted by all snakes for the second (1956), and
third (1957) winters. On 10 January 1956 I marked nine snakes from
a den near Station 153, and released each at the entrance hole.
Though the next day was several degrees colder, not a single snake
was present in this den. Even though they make an escape run on
release, I find it difficult to believe that these serpents could not find
their way back to their den.
I conclude that snakes move away from the site of a den disturb-
ance, and do not re-enter the den for at least 2 years. Perhaps they
move off in response to the normal shock pattern of behavior and are
too cold to return, but this does not explain their absence in subse-
quent years. It has been suggested (I.L. Brisbin, Jr.-pers. comm.)


Vol. 14


that musk sprayed during capture is a warning device. Musk would
have to persist for several years to explain den desertion, and this
theory does not explain why some dens are re-used by other snakes.
Another theory supposes mass movements to winter in other parts
of the peninsula, which the general location of winter captures (Fig.
13) does not support. As I found the denning sites of only a small
percentage of the total population, I could possibly have overlooked
many of them but I felt that I had discovered most of the den sites in
the Gardner's Point area where I made these observations.
Published accounts of den re-use are limited and conflicting.
Hirth (1966) found that 9 out of 10 Crotalus viridis returned to dens
after displacement of 50 to 774 m. Den abandonment, or specific
crevice abandonment, might be inferred from Fitch's (1960) data an
Agkistrodon mokeson. Of 492 copperheads Fitch captured during a
10-year period, apparently only 11 were recaptured on the ledge
where the original captures were made, and only 3 of these at the
exact crevice. It is possible that all the snakes might have returned
to the identical crevice had they not been disturbed. Fitch (1949)
and Woodbury (1951) note that there may be a difference in
whether a snake is allowed to emerge normally to be trapped or
caught or whether it is disturbed in situ and physically removed
when its instincts direct it to remain underground.
I suggest that some crotalid snakes may have a persistent site
memory. Rattlesnakes, successfully adapted to cold climates and
large homiotherm prey, have developed the ability to migrate long
distances to and from specific dens. Cottonmouths have been known
to migrate up to 1/2 mile (Dundee and Burger, 1948) and presumably
have the same instincts. If these snakes have a highly developed
directional sense, perhaps the site memory is also strong and enables
them to avoid disturbed dens. Evidence to support such a theory of
den avoidance is weak, but if cottonmouths do have such associative
powers, my data suggest that this ability may persist for at least 2

Cottonmouths appeared disinclined to move at 8.0C and below,
but from 10.0 to 12.00C followed the usual escape pattern of remain-
ing until one leaves, then moving away. Generally snakes handled
with a CT (cloacal temperature) of 8.0-10.00C were passive and
only gaped, though one 1524-mm male with a CT of 9.0C squirmed
continuously on being handled and finally bit itself twice. At the




lowest CTs recorded (4.0, 4.1, and 4.50C from three snakes 12
February 1955) all were passive and only two sprayed musk-the one
with a CT of 4.0C sprayed musk copiously. A 1118-mm male at
CT 4.5C swelled up and struck several times after being annoyed.
Warning by opening the mouth or gaping first occurred at a CT of
6.50C, with musking and inflation.
In one den three individuals with CTs of 10.0, 11.1 and 11.3C
seemed aggressive towards the snake stick. All three struck it, and
two bit the leather noose. Two inflated and one attempted to vi-
brate the tail, which at this temperature is a feeble and slow move-
ment. These snakes were passive until touched. Two bit the stick
while being withdrawn from the den. At 9.0-100C some snakes
partially coiled when touched. One snake with a CT of 11.0C
crawled out of a hole when molested. A 406-mm young, disturbed
under a palmetto frond, was violently aggressive at CT 11.40C.
About half the cottonmouths threatened at this temperature.
Of 11 snakes whose demeanor was recorded between 4.5 and
10.0C, 4 were aggressive and 7 were passive. This high incidence
of aggression may be due to rough handling, although aggression
would have survival value when snakes are immobilized by cold. I
noted a cottonmouth vibrating its tail at a CT of 12.20C. At 15.0-
16.0C cottonmouths were able to snap into a coil fairly rapidly, and
I noted unprovoked crawling at this temperature. Figure 9, showing
numbers of snakes captured at each degree of air temperature,
shows four snakes captured under nest trees at an air temperature
of 14.40C. These snakes, two of which were actually swallowing fish
at the moment of capture, had CT's of 14.5, 15.8, 15.2, and 15.40C.
The leaf mold temperature was 16.80C and the soil 19.80C, so the
snakes were feeding on a warm substrate. Island cottonmouths may
thus feed at 3.80C below the 18.30C recorded by Allen and Swindell
From these observations I conclude that cottonmouths in this area
become attracted to food and are able to scavenge at a CT of 14.00C
and are quite active at a CT of 16.0C. Figure 10 suggests that the
optimum temperature for these snakes lies between about 180C and
29.50C, somewhat lower than the preferred substrate temperature of
35.340C mentioned by Bogart (1949).
I have noted sunning activity in November between 10.0 and
20.0C (Fig. 10). The coldest day on which I captured a cotton-
mouth sunning was 6.10C; this snake (CT 100C) had crawled
out of a gopher hole den at Station 40.


Vol. 14



55 f

50 --


40 4

40 44 48 52 56 60 64 68 72 76 80 84 88
4.4 6.7 8.9 11.1 13.3 15.6 17.8 20.0 22.2 24.4 26.7 28.9 31.1


FIGURE 9. Cottonmouth captures
or body position.

at specific air temperatures, indicating behavior

The warm-up of a dark, basking cottonmouth is relatively rapid.
On 10 March 1957 I placed a large, completely docile female on dried
grass background of a neutral color on the open beach. The sun was
at an approximate angle of 40W. The sand under the grass at a depth
of 25 mm had a temperature of 15.40C, the humidity was 78 per cent,
and the snake was uniformly dark. The thermometer was gently in-
serted about 36 mm into the cloaca and held in a central position.
Seven readings taken from 09:13 to 09:40 showed the snake's tempera-


30 +



F- 36
C- 2.2




ture rose from an initial 8.80C (air 11.30C) to 21.50C, a rise of 12.7
degrees. During the first 6 minutes the temperature rose 0.9 C per
minute, and thence roughly 0.40C per minute for the remaining 21
This snake was so docile, neither swelling nor moving during the
entire test, that I gently moved it to a shady area beneath the man-
groves and recorded the rapidity of heat loss. The air temperature
remained at 12.00C and the shaded sand covered by dead leaves also
registered 12.0C. I took 11 cloacal readings at 5-minute intervals
while the snake's temperature dropped to 14.80C, a loss of 6.7C in
60 minutes. For the first 15 minutes the heat loss was approximately
0.20C per minute, thereafter for 7 readings, 0.10C per minute. Some
physiological control over rate of change, as Bartholomew and Tucker
(1963) note for a lizard, is possible.
During this test the importance of central cloacal temperature was
demonstrated. Turned so that it rested against the body wall on the
shaded side of the snake the thermometer showed a drop of 0.30C; but
held against the side of the snake in the sun it registered 4.6 C higher
than central cloacal temperature.
During the winter Sea Horse Key snakes often remain in one posi-
tion for considerable periods of time. I saw five individuals that had
remained coiled in one spot on the ground for at least 24 hours. Two


W 15


2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32
FIGURE 10. Observations on 387 cottonmouths captured at specific cloacal tem-
peratures, indicating behavior or body position.


remained in one spot 72 hours without moving. Others seemingly
moved only 5 m or less in 72 hours.
Demeanor on approach was noted on 50 per cent of the cotton-
mouths. Such information renders at best only a crude picture of the
behavior of the snakes, as one does not always approach at the same
speed. Some snakes are approached more cautiously because of
ready refuge near. Others appear to be asleep. Reactions were
classed in five categories: violently aggressive, aggressive, warning,
passive, and escape. The first two involve striking; warning signifies
opening the mouth (gaping); escape means any attempt to crawl
away. Between 4.4'C and 15.60C 36 per cent of the snakes captured
showed aggressive behavior. This contrasts with approximately 4.1
per cent between 15.6 and 32.2'C. No escape reactions were
noted between 4.4 and 10.0C. Between 10.0 and 5.60C 6.8 per cent
tried to escape, and 4.6 per cent between 15.6 and 21.10C. However,
at higher temperatures (to 32.20C) 17.5 per cent of snakes tried to
escape. Lueth (1941), working with young water snakes of the genus
Natrix, noted a tendency to escape at temperatures above 270C.


Volsoe (1944), St. Girons (1957), Tinkle (1957, 1962) and
Wharton (1966) have discussed the relation of body fat to reproduc-
tion in snakes. Body fat also forms an important energy reserve for
snakes. Benedict (1932) shows that during fasting, the respiratory
quotient quickly becomes that of pure fat (0.72).
Cottonmouths carry body fat in two long bundles ventral to the re-
productive and excretory organs. Though it clings tightly in the vi-
cinity of the spleen and gall bladder, it may be stripped out almost as
a discrete unit. Figures 11 and 12 show weights of fat bodies dis-
sected from snakes collected on Snake and Sea Horse Keys. Large fat
bodies are white or yellowish. When depleted they appear as two
coiled orange bands; these were classed as negative fat, and symbols
representing them appear in the graphs along the abscissa. Far
more Sea Horse Key snakes had negative fat bodies than did those
from Snake Key. This supports my earlier statement (1966) that 50
per cent of the Sea Horse Key cottonmouths gained no weight during
the study.
Benedict (1932) demonstrates a direct relationship between meta-
bolic rate and higher temperature in reptiles, and notes that the heat
production of all cold-blooded animals is extraordinarily uniform. A
snake's surface area (S) may be computed by the formula S=





Snake length Snake weight Calculated No. of 46-g fish yielding
(mm) (g) fat weight (g) caloric equivalent

457 53 13.6 2.1

800 475 59.5 9.1

940 907 91.4 13.9

1168 1404 122.2 18.6

1422 2608 185.8 28.3

K X/W, where K is a constant (12.5) times % weight in grams.
Using values from Benedict's rattlesnake curve, I computed the grams
of fat needed by five cottonmouths of varying sizes (Table 6). As the
weight-length data show that Benedict's rattlers were well-fed, heavy
specimens, I selected five fat cottonmouths. While the body surface

o *
0 *



o B


I I I I 1 I I I I e I

3 4 5 6 7 8 9 10 II

12 13 14

FIGURE 11. Fat-body weight in grams versus length of Snake Key cottonmouths.
Curves indicate weights of fat bodies for winter survival. Captures
below zero grams indicate negligible fat bodies. A, cold winter
(1954-55); B, warm winter (1956-57); solid symbols, nonfeeding
period (1 Oct.-28 Feb.); open symbols, feeding period (1 Mar.-30

108 ;

56 -





15 16


Vol. 14


64 -
Z56" o
S48- 0
-40- 0
o o
ce 0
32- o
S0 o o
1 24 0 o B
6-- 0 00 0

8 B00 0 0 A
0-- *o 0--- 0
__ -oo 0 0

A &
3 4 5 6 7 8 9 10 II 12 13 14 15 16
LENGTH (MM x 100)
FIGURE 12. Fat-body weights in grams versus length of Sea Horse Key cotton-
mouths. Curves indicate weights of fat bodies for winter survival.
Captures below zero grams indicate negligible fat bodies. A, cold
winter (1954-55); B, warm winter (1956-57); solid symbols, non-
feeding period (1 Oct.-28 Feb.); open symbols, feeding period (1
Mar.-30 Sept.).

of an emaciated snake almost equals that of a fat one, Benedict's con-
stant requires snakes of reasonable similar condition.
The formula gives a figure which, divided by 10,000, yields the
approximate calories needed by a cottonmouth of these surface areas
per 24 hours. This figure was multiplied by the number of days in the
seasons considered. Curves were drawn to connect points plotted for
each of the five snakes mentioned above for both warm and cold
winters at Sea Horse and Snake Keys (Fig. 11, 12). Curve A, figure
11, shows that 6 of 30 winter captures (20%) on Snake Key had less
fat than needed to survive a winter as cold as the 1954-55 season
(monthly mean, 16.30C), curve B that 11 of 30 winter captures (36%)
had inadequate fat reserves for a winter as warm as 1956-57, (monthly
mean 18.70C). In addition, a winter as warm as the latter would en-
danger 13 of 38 summer captures (34%) unless their fat reserves were
These figures may be contrasted with those of the Sea Horse Key
population (Fig. 12) where, in the colder of the two winters 17 of 31


(55%) had inadequate fat reserve, while 24 of 31 (77%) had insuffi-
cient fat reserves to survive a 5-month winter period similar to that of
the 1956-57 season. On Sea Horse Key 52 of 79 summer captures
(66%) had inadequate reserves to meet a warm winter.
Lueth (1941) found that the rate at which snakes utilize their
energy reserves during starvation varies directly with air temperature.
Volsoe (1944) concluded that the European viper evinces no observ-
able reduction of fat bodies during hibernation, but that these bodies
become reduced after long starvation or during pregnancy.
The cottonmouths showed no marked difference in their fat-body
weights in summer and winter (Fig. 11, 12).
While undoubtedly useful for both males and females in reproduc-
tion, evidently the major function of fat bodies is to provide energy
during warm weather when food is scarce and, although they are not
markedly reduced in normal winters, they serve to offset the effects of
unseasonal warmth during the cooler parts of the year when little food
is available or digestion impossible.
Figures 11 and 12 show that the fat body weights needed for
average winter survival are not high, but a prolonged winter warm
spell subjects cottonmouths to emergency demands on stored fat,
particularly as they do not go into deep dens where the temperature
remains uniform throughout the winter. Winter warm spells occur
frequently in Florida-the extreme warm period in December of 1956
and the mild period that persisted into February over much of
northern Florida in 1957 are examples. Volsoe (1944) suggests that
cold winters are more favorable to hibernating vipers than mild ones.
To the island cottonmouths the winter warm spells may be critical;
following the warm spell in January and February of 1957, I picked up
eight dead snakes. Evidently fat reserves are more important for
snakes in the variable climate of the southeastern United States than
for either northern or tropical forms that live in uniformly cold or
warm temperatures.
The statistical relationship of fat weight to snake length was in-
vestigated in snakes from both Sea Horse and Snake Keys. The sexes
were treated separately and subjected to four F-tests. Only with the
males of Sea Horse Key did the fat weight increase exponentially
with increasing length. For females from Sea Horse Key and males
from Snake Key, a linear equation best expresses the relationship
between fat and total length. Neither curve appeared to fit the data
for females from Snake Key. No relationship between fat weight and
total length was apparent.


Vol. 14


Energy demands are larger in small snakes because of their pro-
portionately larger surface area. During warm seasons food needs
rise to high levels, and unless it eats promptly, a snake with negligible
body fat must begin converting its own protein into energy. Negative
fat bodies in Sea Horse Key snakes occur most consistently in spring
and summer. Figures 11 and 12 have no curves for the fat require-
ments of the five snakes during the warmer months. Their energy
requirements (in fat) from March through September, were com-
puted by using the mean (25.30C) of the three 7-month feeding
seasons (Table 6). The number of fish needed to supply these
amounts of energy for the warm months was calculated. Mattice
(1950) gives the average caloric yield of protein and fat from 6 com-
mon marine fish as about 300 calories per 277 g of fish. The average
length of pinfish eaten by cormorants is about 115 mm; toadfish, about
127 mm. Fish of these measurements weigh about 46 g. Table 6 lists
the approximate number of fish of this size necessary to maintain
cottonmouths at 25.30C for the warm period from March through
September, providing growth demands are ignored.
Sea Horse Key snakes have various ways of offseting rapid heat
loss. Undoubtedly tight coiling reduces the exposed surface area.
The snakes also take refuge in holes or under thick cover at high
environmental temperatures. On very hot days it is often difficult
to find snakes at all. On one occasion, when snakes were avoiding
the open rookery area (33.3C, rel. hum. 54%), I found them 50 m
away beneath dense canopy (31.70C, rel. hum. 62%). I noted 3
snakes seeking den holes in excessively hot weather.
The frequency of negative fat bodies and the randomness of the
fat body weights in reference to the length of the snakes (Figure
12) suggest that many Sea Horse Key snakes lead a precarious
borderline existence, with competition and chance operating to pro-
duce a haphazard food intake. The Snake Key population is better
A factor difficult to assess is water supply. Klauber (1956)
records rattlesnakes drinking water from their own skin and from
the surface of rocks and outlines the reasons why snakes require little
water. While I have seen young cottonmouths suck up water from
leaves or the backs of other snakes after being sprinkled, I have not
observed this behavior in adults. Adult cottonmouths should be able
to drink limited amounts of rain water caught in curled leaves.
Possibly dehydration, as well as food shortage, is an important factor
in snake survival on these islands.




The remains of 20 snakes found dead were measured in the field
and compared with the closest matching sizes of prepared skeletal
material; only one of the dead snakes would have had a total length
less than 1000 mm. The mean length of the 20 snakes was calculated
to be 1291 mm, their mean weight 1634 grams.
The chief cause of death is probably starvation, though dehydra-
tion may also be important. Most dead snakes appeared thin and
emaciated. I have found a number of individuals in a moribund
condition with scarcely enough vitality to crawl.
Death may sometimes be due to other causes. I once found a
large male that appeared to have been in good condition before death.
The posterior end of a linguatulid worm completely blocked the
Adult cottonmouths apparently have few enemies on Sea Horse
Key. Rats do not seem to disturb live cottonmouths, nor do they
molest dead snakes. Possible predators of young cottonmouths are
the red-shouldered hawk and various species of herons. Walter
Auffenberg (pers. comm.) once saw American egrets feeding on
young cottonmouths in roadside ditches between Daytona Beach and
Deland, Volusia County, Florida. Allen and Swindell (1948) state
that herons and cranes eat young moccasins, and mention a Great
Blue Heron choked to death on a cottonmouth it had stabbed through
the head.
Barbour (1956) found a cottonmouth half devoured by a raccoon.
A few snakes are possibly eaten when raccoons are present on Sea
Horse Key.
Eyes are apparently not important to the survival of island cotton-
mouths. Two healthy male snakes were captured that were uniformly
and bilaterally blind, suggesting a genetic cause. There was no
macroscopic vestige of pupil-the supraocular scales nearly touched
the upper labials. Number 131 (total length 1200 mm), in good con-
dition, was captured 4 times between January 1955 and April 1956.
Once, it was struggling for possession of a fish with another snake.
Number 153 was actually fat (total length 1245 mm, weight 1517
g) and was captured 3 times between June 1955 and November
1956. Both snakes were in as good or better condition than the aver-
age island snake. If this blindness is genetic it suggests the intriguing
possibility that eyelessness might compete successfully with the eyed
condition on this island, as food is apparently detected best by olfac-


Vol. 14



The cottonmouth is believed to have descended from an Asiatic
viperid that crossed the Bering land bridge in late Miocene (Neill,
1964) to become an element of the Arcto-Tertiary forest fauna. It
has been present in Florida since the Pleistocene (Brattstrom, 1953;
Auffenberg, 1963) where it has evidently preserved an endogenous
biennial sexual cycle inherited from viviparous ancestral forms (Whar-
ton, 1966). This adaptation to cold climates serves the snake well in
the food-scarce environment of the Cedar Keys.
Various authors (Hamilton and Pollack, 1955; Dundee and Bur-
ger, 1948; Allen and Swindell, 1948) have found mainland cotton-
mouths in dry habitats, often far from water. The migration of main-
land progenitors from one drying pond to another has probably
equipped this snake to cope with different habitats and to seek food
actively on dry uplands. Such vagility, coupled with the develop-
ment of excellent olfaction, enables the island snakes to find and ex-
ploit both the rookeries and the indigenous vertebrates. The swamp-
dwelling specialization has resulted in an ability to feed on both
warm and cold-blooded prey, including dead fish, which fits it per-
fectly as a rookery scavenger. Its wide temperature tolerance and
the absence of notable behavioral thermoregulation is probably an
adaption to a cool, amphibious swamp life, allowing it to survive in a
canopied forest where feeding at low temperatures is often neces-
Cottonmouths have been reported not to feed in zoos in winter
(Conant, 1929). This trait may vary between populations. The
Cedar Keys cottonmouths feed in winter and at that season augment
their warm-season scavenging diet with litter-feeding mammals and
birds. The ability to forage both by active pursuit and by ambush
serves them well on a year-round basis on the island. At the same
time its odor and venom exempt it from predation by most mammals.
The young retain a primitive color pattern, shared with the cop-
perhead, that affords protective coloration in upland deciduous forest
leaf litter. Young cottonmouths are cryptozoic in habits, feeding
largely on lizards and frogs lured by worm-imitating tail tips (Whar-
ton, 1960), a characteristic shared with other members of the genus.
The adult cottonmouth usually loses its primitive, juvenile pattern by
darkening-and thus blends well with the normal swamp substrate.
Increased size, more venom, secretiveness, and nocturnality enable
the adult to offset its lack of protective coloration in upland habitats.
The cottonmouth is able to move into deciduous forests in the




winter and seek underground safety in a wide variety of refuges, in
habitats entirely different from its summer haunts. This ability has
not only led to ease of ecesis on the Florida coastal islands, but has
encouraged the development of a homing ability and, perhaps, a
persistent site-memory.
The Snake Key population survives well entirely by scavenging,
as competing and potentially-edible rodents are absent. Both Snake
and Sea Horse populations exist in high numbers partly because of
the legal protection afforded the rookeries; reciprocally the presence
of so many venomous snakes must deter human molestation at crucial
periods in the birds' life cycle.
The cottonmouth thus appears almost ideally preadapted to ex-
ploit the unique habitat offered by the outer islands of the Cedar
Keys. The niche might be termed that of a terrestrial carnivore-


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Vol. 14

\ K ,' -,>v r

Contributions to the BULLETIN OF THE FLORIDA STATE MUSEUM may be in any
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