seven cottonmouths in Florida. I was given notes of a similar nature by
Richard S. Funk of Junction City, Kansas, on a brood of five
cottonmouths. The mother of the brood was caught in June, 1962, in
Tarrant County, Texas, by Richard E. Smith, and was 705 millimeters in
snout-vent length. The first young was found dead in an extended
position a few inches from the fetal membranes at 11:05 p.m. on August
22. The second young was born at 11:07 p.m. The intervals between the
successive births were three, seven, and four minutes; and time until
the sac was ruptured in each instance was six, five, eight, and 11
minutes. The time interval between the rupture of the sac and emergence
of each individual was 41, 92, 154, and 34 minutes. The mother's actions
in giving birth to the last four young were essentially as described by
Wharton (_loc. cit._), except that the intervals between successive
births did not increase. Within one minute after rupturing the sac and
while its head was protruding, each of the four living young opened its
mouth widely from three to seven times, then took its first breath.
Breaths for the first three hours were steady at three or four per
minute but then decreased to two or three per minute. Pulse rate for the
four averaged 38 per minute while at rest but increased to 44 per minute
after voluntarily crawling.
Number of Young per Litter
Records of from one to 16 young per litter have been reported (Ditmars,
1945:330; Clark, 1949:259), but the average is probably between six or
seven. Most accounts in the literature present information on number of
ova or embryos per female rather than the number of young. Size and age
of the mother (Table 9) influence the number of ova produced. Allen and
Swindell (1948:11) recorded three to 12 embryos in 31 cottonmouths
varying in total length from 26 to 44 inches. An average of 6.5 embryos
per female was found.
TABLE 9.--Number of Ova Produced by Fecund Cottonmouths.
====================+============+======================
Snout-vent length | Number | Number of ova,
in millimeters | in sample | average and extremes
--------------------+------------+----------------------
450-549 | 10 | 4.1 (2 to 7)
550-649 | 11 | 4.9 (1 to 8)
650-749 | 4 | 6.3 (4 to 8)
750-849 | 1 | 5
850-949 | 1 | 14
--------------------------------------------------------
Mortality at birth has been recorded for almost every litter born in
captivity (see Allen and Swindell, _loc. cit._; Conant, 1933:43;
Wharton, 1960:125). A female that I kept in captivity gave birth to
seven young. Three never ruptured their sacs, and another died soon
after leaving the sac. The effects of captivity on females may result in
higher rates of deformity and mortality in young than is common in
nature. Klauber (1956:699-700) estimated that the defects brought about
by conditions of captivity on rattlesnakes eliminate about three young
per litter.
Population Composition
No investigator has yet analyzed the composition of a population of
cottonmouths according to age, sex and snout-vent length. Barbour
(1956:35) did sort 167 snakes into size classes, but did not determine
sex ratio, size at sexual maturity, reproductive cycles, or snout-vent
length. He recorded total lengths from which snout-vent lengths cannot
be computed because of differential growth rates and different bodily
proportions of the two sexes. I judge from my findings that he included
immature individuals in his three smallest size classes (45.5 per cent
of the population). I found at least 32.5 per cent immature individuals
(Fig. 5) in my material, but it was not a natural population.
The sex ratios of several small collections from natural populations
varied, and no conclusions could be drawn. Females comprised 53 per cent
of the specimens included in Fig. 5 and in a group of 48 embryos which
represented eight broods. That percentage may not be the percentage in a
natural population but is used in making assumptions because I lack
better information.
Reproductive Potential
If data in Fig. 5 are representative of a natural population and if 61
per cent of the females are sexually mature, the reproductive potential
can be estimated as follows: assuming a cohort of 1000 cottonmouths
contains 530 females, 61 per cent of the females (323 individuals)
probably are adults. If 42 per cent of these females produce 6.5 young
per female in any season (Tables 8 and 9), 136 females will produce 884
young. But if 50 per cent of the adult females are reproductive (as
would be assumed if reproduction is biennial), 1050 young will be
produced. Actually the number of young required per year to sustain a
population is unknown, because mortality rates at any age are unknown.
[Illustration: FIG. 5. Composition of a group of cottonmouths examined
in this study. Individuals less than 450 millimeters in snout-vent
length are considered as immature. Specimens from 200 to 249 millimeters
in length are included in the 200-millimeter class, _etc._]
GROWTH AND DEVELOPMENT
Size at Birth and Early Growth
Size at birth depends on the health of the mother. According to Fitch
(1960:182), many litters of copperheads born in captivity are stunted.
Seven young cottonmouths (two males and five females) born in captivity
were each 185 millimeters in snout-vent length and 40 millimeters in
tail length. Weights of the three living young were 10.0, 10.1, and 11.1
grams. Another litter of five young measured by Richard S. Funk were
larger, and differences in the proportions of the tail length and
snout-vent length suggest the sexual dimorphism found in larger
individuals. However, sex of these young snakes was not recorded.
Snout-vent length and tail length in millimeters were 232, 41; 243, 47;
229, 40; 240, 48; and 225, 40 in the order of their birth. These snakes
are considerably smaller than the nine young of _A. p. piscivorus_
reported by Wharton (1960:127) that averaged 338 millimeters total
length and 28.7 grams. The yolk of one young _piscivorus_ was 11.7 per
cent of the total weight. Yolk is used up in about two weeks if its rate
of utilization resembles that of the copperhead as reported by Gloyd
(1934:600).
Early rates of growth of three living young are shown in Table 10. On
the 56th day after birth, each was fed one minnow less than two inches
long. Between the 80th and 120th days three additional small minnows
were fed to each snake. Young cottonmouths increase nearly 50
millimeters in length by the first spring if they inhabit warm areas and
feed in autumn or winter.
Variation in size of newborn cottonmouths may be less in nature than in
captivity. Average size at birth can be determined accurately by the
size of young captured in early spring, at least in northern parts of
the range where winter feeding and growth do not occur at all or are
negligible. Total lengths of 19 juveniles thought by Barbour (1956:38)
to be seven to eight months old do not differ markedly from lengths of
the five newly-born young measured by Funk.
TABLE 10.--Rate of Growth of Three Young Cottonmouths.
========+=================================================
| | Snout-vent length/tail length--weight in grams |
| Age +----------------+----------------+----------------|
|in days | Female No. 1 | Female No. 2 | Male |
|--------+----------------+----------------+----------------|
| 2 | 185/40--11.1 | 185/40--10.1 | 185/40--10.0 |
| 7 | 192/40-- | 190/40-- | 189/40-- |
| 22 | 195/40--10.3 | 200/41.5--10.6 | 197/40-- |
| 80 | 204/40--11.7 | 203/42--10.4 | 218/48--14.3 |
| 88 | .... | 204/44-- | .... |
| 143 | 215/40.5--13.3 | .... | 225/48--15.1 |
--------+----------------+----------------+----------------
The Umbilical Scar
The umbilical cord is broken at birth and the navel closes within a few
days; but the scar, involving from two to four ventral scales, remains
throughout life. Position of the scar was found by Edgren (1951:1) to be
sexually dimorphic in the eastern hog-nose snake (_Heterodon
platyrhinos_), but nothing has been published on this matter concerning
the cottonmouth. Consequently, I counted the scales of several
individuals from the anal plate, and there was no marked difference in
the position of the scar in males and females; it varied in position
from the 10th to the 18th scale. When counted from the anterior end, the
scar ranged from ventral number 115 to 122 (average, 119) in 28 females
and from number 117 to 126 (average, 121) in 14 males. The difference
between male and female cottonmouths is not nearly so great as in
_Heterodon_.
Later Growth and Bodily Proportions
The only records of growth increments in a natural population of
cottonmouths are those in Table 11. The period of growth is mostly the
period of activity, and differences are expected between northern and
southern populations. As size increases, determination of growth rate
becomes more difficult because age classes overlap in size. Growth of
any individual depends not only on climate and food but also on disease
and parasitism and the innate size potential. Stabler (1951:91) showed
weight and length relationships in two cottonmouths for a period of six
and one-half years.
TABLE 11.--Growth Increments in Cottonmouths (Barbour,
1956:38-39).
=============================================
| Number of | Total |Estimated| Estimated |
| | length | age | growth |
| | | | from |
| | | | preceding |
| | | | year |
|individuals| in |in months| in |
| |millimeters| |millimeters|
|-----------+-----------+---------+-----------|
| 19 | 260-298 | 7-8 | 25 |
| 11 | 312-337 | 19-20 | 45 |
| 40 | 355-485 | 31-32 | 95+- |
| 83 | 500-1000 | 43-44+ | ? |
---------------------------------------------
My study failed to reveal any secondary sexual difference in growth rate
and maximum size. Of the 306 cottonmouths measured by me, 16 males and
five females exceeded 700 millimeters in snout-vent length. Two males
were more than 850 millimeters long. One cottonmouth lived in captivity
for 18 years and 11 months (Perkins, 1955:262). The maximum total
lengths were reported by Conant (1958:186-187) to be 74 inches (1876
mm.) in _A. p. piscivorus_ and 54 inches (1370 mm.) in _A. p.
leucostoma_.
[Illustration: FIG. 6. Head length (º) and head width (.) expressed as a
percentage of snout-vent length of living and preserved cottonmouths.
Head length was measured from the tip of the snout to the posterior end
of the mandible. Head width was measured across the supraocular scales,
since accuracy was greater than if measured at the posterior edge of the
jaw. No sexual dimorphism or geographical variation occurs in these
characters.]
Proportions of various parts of the body vary considerably depending on
age, size and, in some instances, sex. Heads are proportionately larger
in young than in adults (Fig. 6), as is true of vertebrates in general.
This larger head has survival value for the cottonmouth in permitting
more venom to be produced and in permitting it to be injected deeper
than would be the case if the proportions were the same as in adults.
Relative to the remainder of the snake the head is considerably larger
than in the copperhead (Fitch, 1960:108) and slightly larger than in the
rattlesnake, _Crotalus ruber_ (Klauber, 1956:152).
[Illustration: FIG. 7. Tail length expressed as a percentage of
snout-vent length of living and preserved cottonmouths (.--males;
º--females).]
In general, tails are relatively longer in males than in females of the
same size (Fig. 7), except that there is little or no difference at
birth. Growth of the tail in males proceeds at a more rapid rate. In
certain individuals sex cannot be recognized from length of the tail
relative to snout-vent length because overlapping occurs, especially in
medium-sized individuals. Similar changes of proportions with increase
in age occur in copperheads (Fitch, 1960:106) and rattlesnakes (Klauber,
1956:158-159), but the tail of the cottonmouth is relatively much
longer.
SHEDDING
The Shedding Operation
Shedding of the skin is necessary to provide for growth and wear in
snakes. The milkiness or bluing of the eyes, which causes partial
blindness, marks the initial stage of shedding and is caused by a
discharge of the exuvial glands that loosens the old _stratum corneum_
from the layer below. In four to seven days the opaqueness disappears,
and the snake sheds after an additional three to six days (Table 12).
Young snakes first shed within a few days after birth and generally shed
more frequently than adults, but the interval is variable. The eyes of
three young cottonmouths observed by Wharton (1960:126) became milky on
the fourth day but cleared on the seventh day, and the skin was shed on
the eighth day. The eyes of three young kept by me became milky two to
three days after birth, cleared on the seventh to tenth days, and the
skin was shed on the thirteenth day. Possibly the relatively long
interval in this instance resulted from low relative humidity in the
room where the snakes were kept. According to Fitch (1960:134), litters
of young copperheads usually shed within three to ten days after birth;
but under unusually dry conditions shedding did not occur for several
weeks.
TABLE 12.--Duration of Preparatory Period (in days) to Shedding
in 11 Cottonmouths.
==============================
|Duration | Time |Time from |
| of |between |beginning |
|cloudiness|clearing| of |
| | and |cloudiness|
|of eyes |shedding| until |
| | | shedding |
|----------+--------+----------|
| 5 | 6 | 11 |
| 7 | 3 | 10 |
| - | - | 6 |
| - | - | 6 |
| 5 | 3 | 8 |
| 4 | 6 | 10 |
| 7 | 3 | 10 |
| 5 | 6 | 11 |
| 5 | 3 | 8 |
| 7 | - | - |
| 7 | 3 | 10 |
| ---- | ----| ---- |
|[=X] 5.4 |[=X] 3.8| [=X] 9.0 |
------------------------------
Cottonmouths as well as other snakes usually do not feed until after the
skin is shed and are generally quiescent during the period preceding
shedding, except that immediately before shedding they become active and
rub their snouts on some rough object and may yawn several times
seemingly in an attempt to loosen the skin along the edges of the lips.
After the skin is loosened from the head, more rubbing against rough
surfaces and writhing serves to pull the old skin off, turning it inside
out. Once the old skin has passed over the thick mid-body, the snake
often crawls forward using rectilinear locomotion until the skin is
completely shed. It normally comes off in one piece; but, if the snake
is unhealthy or has not had sufficient food or water, the skin may come
off in patches. Frequently one or both of the lens coverings are not
shed immediately and impair the sight. Bathing or swimming ordinarily
causes dried skin to peel off; and, because of the cottonmouth's aquatic
habits, its chances of shedding successfully are much greater than those
of less aquatic snakes. Cottonmouths that have recently shed have bright
and glossy patterns, in contrast to the dull and dark appearance of
those that are preparing to shed.
Frequency of Shedding
Most of our knowledge concerning the frequency of shedding is based upon
observations of captives. It is known that the intervals between
exuviations are largely dependent upon the amount of food taken and the
rate of growth. Unless laboratory conditions closely resemble those in
the field, shedding frequencies in captives probably differ much from
those of free-living snakes.
Only two of my captives shed twice. The intervals between exuviations in
the two snakes were eight and five months, lasting from August to April
and from December to May, respectively. Ten other snakes shed once in
the period from January through July. Stabler (1951:91) presented data
concerning shedding of two cottonmouths kept 12 and 14 years in
captivity. One shed 25 times in 12 years and the other shed 37 times in
14 years, giving an average of 2.1 and 2.6 per year, respectively.
Neither of the snakes shed from December through March, but the period
of shedding corresponded to the period of greatest activity and growth.
In Florida, cottonmouths shed four to six times a year, according to
rate of growth (Allen and Swindell, 1948:7).
FOOD HABITS
Methods of Obtaining Prey
Food is obtained by a variety of methods depending on the type of food,
age of the cottonmouth, and possibly other factors. Some captives lie in
ambush and others crawl slowly in active search. At the first cue of
possible prey, either by sight, scent, or differential temperature
detection by the pit, the snake appears to become alert and flicks its
tongue out at fairly rapid intervals.
By means of the facial or loreal pit found in all crotalids, the snake
is able to detect objects having temperatures different from that of the
surroundings of the objects. In detecting prey the tongue acts to
sharpen the sense of "smell" by conveying particles to Jacobson's organs
in the roof of the mouth. On many occasions cottonmouths appeared to
rely solely on sight; they passed within a few inches of prey,
apparently unaware of its presence until it moved. When pools of water
begin to dry up toward the end of summer, cottonmouths often congregate
and feed on dying fish. In these instances the fish are usually taken as
they come to the surface. In laboratory observations moccasins seize
live fish and some moccasins carry the fish until they have received
lethal doses of venom; afterward the fish are swallowed. But grasping
and manipulation of the prey occurs without the fangs' being employed,
especially in the case of dead fish. On one occasion a cottonmouth was
observed to grasp the edge of a glass dish that had contained fish and
apparently retained the odor. On another occasion I placed several fish
in a bowl, rubbed a stick on the fish, and then touched each snake
lightly on the nose with the stick. The snakes crawled directly to the
bowl and began feeding. At other times these same snakes crawled around
the cage in an apparent attempt to locate the food but paid little
attention to fish held in front of them. If the catching of prey under
natural conditions were as uncoordinated as it sometimes is in
captivity, the snakes probably would not be able to survive.
Wharton (1960:127-129) described tail-luring in one individual of a
76-day-old brood of cottonmouths. The snake lay loosely coiled with the
tail held about six centimeters from the ground; a constant waving
motion passed posteriorly through the terminal inch of the tail. These
movements ceased at 7:20 p.m. but were resumed at 7:40 a.m. the
following day. All observations were under artificial light. The "caudal
lure" as a means of obtaining prey has been described in other species
and related genera by Neill (1960:194) and Ditmars (1915:424).
Various authors have suggested that the method of capture differs
according to the kind of prey. Allen and Swindell (1948:5) stated that
cottonmouths retain their hold after striking fish or frogs but will
release a mouse after delivering a bite and are timid in striking at
larger rodents. Neill (1947:203) noted that a cottonmouth always waited
several minutes after biting a large rat before approaching its prey.
This same type of behavior has been reported for copperheads (Fitch,
1960:194) and rattlesnakes (Klauber, 1956:618). Cottonmouths observed by
me retained a strong hold on fish, frogs, and sometimes mice, but almost
always released large mice and baby chicks, which were not eaten until
after death.
Different behavior according to type of prey is correlated with ability
of prey to retaliate, although some animals may not be released because
they could easily escape. For instance, a frog could hop far enough to
escape in a matter of seconds if released. A 73-millimeter _Rana
pipiens_ that I observed was bitten twice within one and a quarter hours
and died 45 minutes after the last bite. Its movement was uncoordinated
by the time of the second bite, but it could have escaped had the frog
not been confined. Although it is doubtful that normal, healthy fish are
frequently captured by cottonmouths, Allen (1932:17) reported that a
cottonmouth was seen pushing a small, dead pike about on the surface of
a stream. A wound on the belly of the fish indicated that it had been
bitten. A 17-gram creek chub (_Semotilus_) and a 13.7-gram bass
(_Micropterus_) were injected by me with one-fourth cubic centimeter of
fresh venom near the base of the tail in order to determine whether the
fish could escape after being bitten and released. The creek chub
flipped onto its back after a minute and 45 seconds and gill movements
stopped in eight minutes and 35 seconds; the bass flipped over after 50
seconds and died in two minutes and 10 seconds. The venom immediately
affected both fish, and it is unlikely that either could have swum more
than a few feet.
After its prey has been killed, a cottonmouth examines the body from end
to end by touching it with the tongue. Then the animal is grasped in the
mouth without the use of the fangs and is slowly manipulated until one
end (usually the head) is held in the mouth. The lengthy process of
swallowing then takes place, the fangs and lower jaws alternately
pushing the prey down the throat.
Food and Food Preferences
The cottonmouth seems to be an opportunistic omni-carnivore, because it
eats almost any type of flesh that is available, including carrion. It
feeds primarily upon vertebrates found in or near water; but
invertebrates and eggs have also been found in the diet. The only
potential prey items that seem not to be normally eaten are bufonid
toads and tadpoles. I have occasionally offered tadpoles and frogs to
cottonmouths, but only the frogs were accepted. But, Stanley Roth kept a
cottonmouth in captivity that ate both toads and tadpoles. If tadpoles
are commonly eaten, their probable rapid digestion would make
identification almost impossible.
Following is a list of known foods of the cottonmouth:
Captivity: "... rattlesnake.... The same moccasin also killed
and ate a smaller snake of its own species...." (Conant,
1934:382.)
Florida: "3 heron feathers, bird bone, _Eumeces inexpectatus_,
3 fish all under one inch in length, 1 heron egg shell" (Carr,
1936:89). According to Allen and Swindell (1948:5), "the food
included other moccasins, prairie rattlesnakes, king-snakes,
black snakes, water snakes, garter snakes, ribbon snakes, and
horn snakes ... most of the species of frogs, baby alligators,
mice, rats, guinea pigs, young rabbits, birds, bats, squirrels,
and lizards ... a mud turtle ... a case of a four footer eating
ten to twelve chicken eggs. The most common food appears to be
fish and frogs. Catfish are included on this list...." Yerger
(1953:115) mentions "an adult yellow bullhead, _Ameiurus
natalis_ ... 306 mm. in standard length [from a 63-inch
cottonmouth]."
Georgia: "... full grown _Rana catesbeiana_, several foot-long
pickerel ... dead fish if placed in a pan of water.... _Natrix
sipedon fasciata_ and _Masticophis flagellum_ ... rats....
Toads and large _Eumeces laticeps_ were always ignored."
(Neill, 1947:203.) "_Natrix_, _Heterodon_, _Kinosternon_,
_Rana_, _Hyla cinerea_, _Microhyla_, Microtine [_Pitymys
pinetorum_]." (Hamilton and Pollack, 1955:3.)
Mississippi: "... _Hyla gratiosa_.... In captivity specimens
have eaten frogs, mice, birds, dead fish, pigmy rattlers and
copperheads. Toads ... were refused" (Allen, 1932:17). One
moccasin "disgorged a smaller decapitated moccasin ... killed
the day before by boys" (Smith and List, 1955:123).
Tennessee: "Beetles in one stomach; lizard (_Eumeces_) in
another stomach; small snake (_Natrix_) in one intestine, and
hair in another intestine. One stomach contained numerous bits
of wood, up to four inches in length...." (Goodman, 1958:149.)
Kentucky: "_Siren intermedia_ was the most abundant food item
in both volume and occurrence. Frogs of the genus _Rana_ ranked
second. Together, these two items comprised almost 2/3 of the
food of the snakes. The other food items were distributed among
the fishes, reptiles, and other amphibians [one _Rana_ tadpole
included]." (Based on 42 samples--Barbour, 1956:37.)
Illinois: (Based on 84 samples--Klimstra, 1959:5.)
_Per cent Frequency_ _Per cent_
_Food Item_ _of Occurrence_ _Volume_
Pisces 39.3 31.9
Amphibia 36.9 26.0
Reptilia 25.0 18.2
Mammalia 30.9 17.9
Gastropoda 17.8 1.0
Miscellaneous 25.0 5.0
(Algae, Arachnida,
Aves, Insecta)