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.

Age
in days		 Snout-vent length / tail length—weight in grams
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
individuals		 Total length
in millimeters		 Estimated age
in months		 Estimated growth
from preceding year
in 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.