Selected aspects of the biology of semi-aquatic turtles in east-central Kansas: Winter thermal profiles and escape behavior

Abstract

Temperate-zone semi-aquatic turtles encounter a wide range of temperatures within their aquatic habitats. However, most of the temperature-related research on these turtles has been conducted during their active season (late March – early October), and information on winter thermal profiles is relatively limited. The development of Thermochron® iButtons, an inexpensive thermal monitoring device, has greatly facilitated such studies. I attached iButtons to 20 male and 20 female Chrysemys picta during summer 2010. These iButtons were preprogrammed to record temperatures at 12 min intervals from 5 December 2010 to 9 April 2011. However, given the paucity of winter thermal profiles in these animals, my analyses focused on winter thermal profiles (5 December 2010 - 21 March 2011). Chrysemys picta shell temperatures ranged from 0.5 to 14 ° C between 5 December 2010 and 21 March 2011. In addition, the first basking activity of C. picta in 2011 occurred 23 February at an air temperature of 10.5 °C and maximum water temperature of 8.1 °C. Turtle temperatures were similar to the minimum water temperatures in the study pond throughout most of the winter. These results were consistent with the conclusions of previous studies that C. picta may voluntarily select low temperatures during winter to delay metabolic acidosis and better conserve stored energy. Researchers commonly use traps to obtain turtles for use in experimentation and to sample populations and assemblages to generate estimates of various community or population level parameters. However, most traps are biased with respect to the probability of capturing different species, individuals of different sizes, or different sexes. An improved understanding of such biases may help researchers generate more accurate estimates of such parameters. Some turtles may escape from traps, but previous studies of escape frequency have reported very different results. Also, past studies have failed to compare escape rates among species or between trap types. To examine trap escape rates, uniquely marked Trachemys scripta and C. picta were placed into basking traps or funnel traps, which were checked after ~24 hr to determine escape. Overall, turtles escaped from traps during 73.6% of the trials. Adult females of both species escaped from basking traps more frequently than males or juveniles. In general, larger individuals (of both species) were significantly more likely to escape from basking traps than smaller individuals. In contrast, body size and sex were not significant predictors of escape from funnel traps for either species. Therefore, funnel traps may provide the least biased sample of these species with respect to sex and body size.