Eastern Cottoiimouth Reproduction 
123 
DISCUSSION 
It is obvious that the limits of a species’ range are reached where 
mortality regularly exceeds reproductivity. At the Hopewell site we have 
established that survival of young cottonmouths is quite poor in years in 
which the winter is unusually cold (Blem and Gutzke, in preparation). 
The success of females giving birth in the lab indicates that reproduction 
regularly occurs without undue mortality. In the field, several litters of 
newborn cottonmouths have also been observed in September. No small 
cottonmouths (i.e less than 403 mm snout-vent length) have been col- 
lected at Hopewell in spring or summer, although we regularly collect 
individuals of 200-500 mm in extreme southeastern Virginia. I believe this 
is related to the extremely cold winters of 1976-1977 (the coldest January 
since 1940) and 1977-1978 (the second coldest January of the period 
1971-1979). No other environmental variable would seem to account for 
the disappearance of young overwinter. The more abundant size classes 
over 600 mm appear to represent greater survivorship over mild winters 
before 1976. 
A variety of forces may contribute to death in cottonmouths. Man is 
probably the major cause of mortality at most sites (Burkett 1966), but 
starvation during mild winters (Wharton 1969), disease and parasitism 
(Burkett 1966), and a wide variety of predators (Allen and Swindell 1948, 
Barbour 1956, Burkett 1966) all take their toll. Mortality from cold seems 
to be absent in the main range, as tolerance of low temperatures seems 
well developed in cottonmouths (Wharton 1969). Perhaps only at the 
northern edge of the range does freezing occur so intensively or for such 
long periods that survival in the hibernacula becomes difficult. 
The ability of a species to maintain its distributional limits or expand 
them depends upon behavioral, physiological, and morphological adap- 
tations that balance the birth-death ratio. Among the reproductive 
adjustments that a reptile might demonstrate are: 1) increased litter size, 
2) more frequent ovulation, 3) earlier sexual maturation, 4) early ovula- 
tion or more rapid development of young, 5) production of young that 
are better adjusted for survival of the environment at the distributional 
extreme, and 6) niche selection that maximizes the accumulation of 
energy for reproduction. 
Few data are available with which to compare litter size at the Hope- 
well site. Litter sizes in cottonmouths collected in the Everglades (x=6.6 ± 
2.5, N=31: Allen and Swindell 1948) do not differ significantly from the 
data in my study. Mean litter size of females from the Cedar Keys, Florida 
(5.5 ± 1.5, N=24; Wharton 1966) is significantly smaller (t=4.8, df=46) 
than that of the Hopewell site. I conclude that there is little evidence at 
present that indicates any adjustment of the number of young in litters at 
the northern extreme of the range. 
