Modeling Onset of Hourly Nesting Activity in a Freshwater Turtle Using Abiotic Variables and Physiological Capacity

Abstract

Nesting is an essential, yet variable, reproductive behavior in most oviparous organisms. Although many factors conceivably influence nesting behaviors, it is unclear which factors strongly influence terrestrial nest timing in aquatic nonavian reptiles. As climate is changing rapidly, understanding the relative influences of biotic and abiotic factors on nesting behaviors may yield important information on future changes in daily and seasonal nesting activity. We collected hourly data to examine the significance of local weather conditions to the timing of within-season nesting activity in a large population of Painted Turtles (Chrysemys picta). We quantified nesting activity as the ratio of females who nested to all females who could nest in each hour, adjusting the size of the denominator to include the time required to shell a subsequent egg clutch. We then used zero-inflated models to identify potential weather predictors of presence/absence of nesting activity and strength of nesting responses (i.e., the fraction of turtles nesting that could nest). Higher temperatures and rainfall predicted stronger nesting responses, whereas lower temperatures and no rainfall predicted the absence of nesting activity, indicating that both temperature and rainfall are important cues in within-season nesting phenology. Our study enhances our understanding of abiotic influences on the terrestrial nesting behavior of aquatic organisms.