Site Selection and Survival of Pseudemys Texana and Trachemys Scripta Elegans Nests at Spring Lake in San Marcos, Texas
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Turtle eggs and embryos may succumb to a variety of causes of mortality, including vertebrate and invertebrate predators. Characteristics of nest sites selected by turtles may influence survival of offspring. Spring Lake in San Marcos, Hays County, Texas supports several native, non-native, and endangered species. It also serves as an educational and recreational area. This study investigated the survival and causes of mortality of the eggs of Texas river cooters (Pseudemys texana) and red-eared sliders (Trachemys scripta elegans) at Spring Lake. A total of 122 nests were monitored during the 2006 and 2007 nesting seasons. Random nests were protected from vertebrate predators and excavated approximately 70 days after oviposition to determine hatchling success, while others were not protected from predation. Combined data from both years reflected a 59.21% (n = 45) predation rate by raccoons on unprotected nests. After excavation, 45.65% (n = 21) of protected nests yielded live hatchlings, 45.65% (n = 21) were unsuccessful, and 8.7% (n = 4) were false nests. Protected nests that were unsuccessful were a result of excessive water (rainfall), desiccation, or various other causes including incomplete development and ants. Six parameters (distance from water, distance from nearest tree, distance from nearest man-made structure, substrate, slope, direction of slope in relation to water, and canopy cover) were recorded from 60 nest sites and 60 random non-nest sites. A MANOVA of these data suggested that nest-site selection did occur (P < 0.0001). Principal Components Analysis (PCA) suggested that distance from water was the principal component in nest-site selection. These data suggest that raccoon predation and moisture-related factors are the primary causes of mortality of turtle nests at Spring Lake.