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.

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