A 21-Year Study of Seasonal and Interspecific Variation of Hatchling Emergence in a Nearctic Freshwater Turtle Community: To Overwinter or Not To Overwinter?

Abstract: 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. Résumé: Le motif d'émergence d'une communauté de 6 espèces de tortue d'eau douce a été étudié, dont Chelydra serpentina, Chrysemys picta, Clemmys guttata, Glyptemys insculpta, Glyptemys muhlenbergii, et Sternotherus odoratus, dans le comté de Lancaster, en Pennsylvanie, É.-U. Les données telles que l'estimé de date d'éclosion, la longueur de la carapace, les précipitation aux mois d'avril et mai et ensuite août et septembre, les précipitations annuelles, et la présence de basses températures et de pluie pendant les 24 h avant la détection d'éclosion de tortues (n  =  806) ont été mesurées annuellement de 1965–1985. Les jeunes tortues des espèces C. serpentina, Ch. picta, and Cl. guttata semblent pratiquer une stratégie d'émergence tardive facultative, leur permettant d'émerger plus tard dans la saison si nécessaire. Les autres espèces (G. insculpta, G. muhlenbergii, et S. odoratus) semblent plutôt contraintes à émerger tôt dans la saison, sauf dans le cas d'une tortue G. muhlenbergii qui a été observé en émergence tardive. Au moins une espèce de tortue a été observée à émerger hâtivement à chaque année, à l'exception de 1973, année précédée d'un sévère ouragan causant l'inondation et la destruction de plusieurs nids. Par contre, la majorité des jeunes tortues ont repoussé leur émergence à l'année suivant l'oviposition. Le jour hebdomadaire moyen d'émergence a varié annuellement pour C. serpentina et Ch. picta. La même variable varie entre espèces lors de comparaisons entre l'émergence hâtive et tardive. Les jeunes C. serpentina émergeaient plus tôt que toutes les autres espèces dans notre étude, peu importe leur stratégie d'émergence. La longueur de la carapace des jeunes Ch. picta a fait preuve de beaucoup de variations à travers les ans, tandis que les jeunes C. serpentina qui ont émergé tardivement avaient une longueur de carapace significativement plus grande que ceux qui ont émergé plus tôt. Les précipitations annuelles et celles reçues dans les 24-h précédant l'émergence avaient des effets variables en termes de nombre de tortues émergentes, mais nos observations semblent indiqués une forte relation entre les précipitations d'août et septembre au nombre de jeunes tortues restants dans le nid jusqu'au printemps suivant. Le nombre maximal de tortues en émergence a été observé quand la température de l'air était de 12°C pendant les 24-h précédentes, observation pour les tortues pratiquant une émergence hâtive ou tardive. Finalement, les espèces de petite taille, comme G. muhlenbergii et S. odoratus, peuvent parfois employer la stratégie d'émergence hâtive afin d'alléger la compétition entre elles et les autres espèces de tortue d'eau douces qui pratiquent principalement la stratégie d'émergence tardive.

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