A 21-year study of seasonal and interspecific variation of hatchling emergence in a nearctic freshwater turtle community: To overwinter or not to overwinter?

Hatchling emergence patterns were studied in a community of six species of freshwater turtles in Lancaster County, Pennsylvania, USA, including: Chelydra serpentina, Chrysemys picta, Clemmys guttata, Glyptemys insculpta, Glyptemys muhlenbergii, and Sternotherus odoratus. Data were collected every year from 1965-1985 on estimated date of emergence, carapace length, April-May precipitation, August-September precipitation, annual precipitation, and low temperature and occurrence of precipitation during the 24 h prior to the time of each hatchling detection (n=806). Chelydra serpentina, Ch. picta, and Cl. guttata hatchlings have a facultative delayed emergence strategy. The other species (G. insculpta, G. muhlenbergii, and S. odoratus) appear to be obligate early emergers, with the exception of one hatchling G. muhlenbergii that delayed emergence. Early emergence occurred in some species every year. However, the majority of hatchlings delayed emergence until the year following oviposition, except in 1973, the year following intense flooding and nest destruction associated with a major hurricane. Mean estimated calendar day of emergence varied annually in C. serpentina and Ch. picta. The same variable also differed among species for comparisons of both early and delayed emergence. Chelydra serpentina hatchlings emerged earlier than all other species whether they used an early or delayed strategy. Carapace length of Ch. picta hatchlings varied significantly among years, and C. serpentina hatchlings that delayed emergence were significantly larger in carapace length than those that emerged early. Seasonal and previous 24-h precipitation had varying effects on the number of emerging hatchlings, but August-September precipitation in one year had a strong correlation with the number of hatchlings that delayed emergence until the following spring. The number of hatchlings detected peaked at a previous 24-h air temperature of about 12°C for both early and late emergence. Small species like G. muhlenbergii and S. odoratus may emerge early to limit potential hatchling competition in diverse communities of freshwater turtles with primarily delayed emergence.