Eurycea quadridigitata Biology 
101 
However, it is clear from Fig. 1 that the initiation of breeding migrations 
is due to a drop in average air temperature over a several day period in 
late summer and early autumn. It should also be noted that breeding 
migrations of E. quadridigitata are probably adaptively adjusted for the 
autumn period since similar environmental conditions from January 
through June did not induce migration to breeding areas. Similar condi- 
tions were noted by Shoop (1960) for initiation of breeding migrations of 
Ambystoma talpoideum in Louisana. 
The breeding migration period on the SRP corresponds with that 
reported by Harrison (1973) for the Charleston, South Carolina area, but 
the onset of movement to the bays on the SRP was about a month earlier. 
Variation in the onset of breeding migrations can be expected because of 
local and annual variation in climatic factors. 
Data concerning the exiting of adults and/or metamorphosing 
juveniles during 1978 are not available since a large proportion of the 
breeding adult population was destructively sampled. 
Population size structure. — Population size structure of E. 
quadridigitata entering Rainbow Bay and Ellenton Bay is shown in Fig. 2. 
All 124 individuals of both sexes entering the bays at this time were 
mature and their sex ratio did not differ from 1:1 (X : = 0.48, df = 1, p > 
0.40, Rainbow Bay; X 2 = 0.08, df = 1, p > 0.90, Ellenton Bay). The mean 
SVL of adults was 29.1 ± 0.20 mm (N = 74, range 24-33 mm SVL) at 
Rainbow Bay and 26.4 ± 0.24 mm (N = 50, range 23-31 mm SVL) at 
Ellenton Bay. Local variation was evident in that adults from Rainbow 
Bay were significantly larger than those from Ellenton Bay (t = 8.77, df 
= 122, p < 0.001). Similar results were noted for metamorphosing E. 
quadridigitata juveniles from two populations (Semlitsch, in press) and 
may be explained by differential growth rates of juveniles in response to 
water temperature and/or food availability (Shoop 1974; Stewart 1956; 
Wilbur 1972; Wilder 1924). Since Rainbow Bay is smaller and more 
shallow than Ellenton Bay, the water may warm more quickly in the 
spring. Larvae from Rainbow Bay may grow more rapidly and gain a 
growth advantage that might be maintained to maturity. 
Sexual dimorphism in body size was not present in E. quadridigitata 
since the SVL of males and females was not significantly different at 
Rainbow Bay and Ellenton Bay (t = 1.35, df = 72, p > 0.20; t = 0.29, df 
= 48, p > 0.50; respectively). 
Size classes other than the unimodal distribution of adults were not 
found entering the bays during breeding migrations (Fig. 2). Year classes 
among adults cannot be distinguished on the basis of size. This could be 
because no growth occurs after sexual maturity is reached or because E. 
quadridigitata is short-lived and few adults survive to breed more than 
once during their life. The evidence presented supports the latter explana- 
tion, since very few adults ever leave the bays after breeding (Fig. 1, see 
1979 season.) 
