Climate effects on nesting phenology in Nebraska turtles
A frequent response of organisms to climate change is altering the timing of reproduction. In particular, advancement of reproductive timing has been a common response to warming temperatures in temperate regions. Over the past three decades in Nebraska, USA, the timing of nesting of the Common Snapping Turtle (Chelydra serpentina) was negatively correlated with mean December maximum temperatures of the preceding year and mean May minimum and maximum temperatures in the nesting year, and positively correlated with precipitation in July of the previous year. Increased temperatures during the late winter and spring likely permit earlier emergence from hibernation, increased metabolic rates and feeding opportunities, and accelerated vitellogenesis, ovulation, and egg shelling, all of which could drive earlier nesting. However, for the Painted Turtle (Chrysemys picta), the timing of nesting was positively correlated with mean minimum temperatures in September, October, December of the previous year, February of the nesting year, and April precipitation. These results suggest warmer fall and winter temperature may impose an increased metabolic cost to painted turtles that impedes fall vitellogenesis, and April rains may slow the completion of vitellogenesis through decreased basking opportunities. For both species, nest deposition was highly correlated with body size, where larger females nested earlier in the season. Although average annual environmental temperatures have increased over the last four decades at our study site, spring temperatures have not yet increased, and hence, nesting phenology has not advanced at our site for Chelydra. While Chrysemys exhibited a weak trend toward later nesting, this response was likely due to increased recruitment of smaller females into the population due to nest protection and predator control (Procyon lotor) in the early 2000s. Should climate change result in an increase in spring temperatures, nesting phenology would presumably respond accordingly, conditional on body size variation within these populations.
Three data sets are included: 1) climate data during study period at field site; 2) nesting phenology and associated data for painted turtles; and 3) nesting phenology and associated data for snapping turtles. Raw data for each data set are included here.
Climate Data set: Weather data from July of the previous year through May of the year of turtle nesting were obtained from the NOAA weather station located immediately adjacent to the turtle nesting area (< 100 m). We tabulated monthly mean maximum (max) and monthly mean minimum (Min) temperatures and monthly rain for each month (3-letter abbreviations) for each year of the study (33 total variables). We did not include data from June since that is the primary month of nesting. All data are in °F or inches of rain, as downloaded from the weather station.
Nesting phenology data sets: Abbreviations include CL (carapace length in mm), PL (plastron length in mm), BM (body mass in grams), CS (clutch size), and EM (egg mass in grams).
National Science Foundation, Award: IOS 1257857
Earlham College Test Fund
Earlham College Test Fund