Behavioral Ecology of Basking in the Yellow-bellied Turtle, Chrysemys scripta scripta (Shoepff)

Abstract

The purpose of this study is to determine if basking in turtles is thermoregulatory and to describe the attendant behavior. Observations were made from a blind on a marked population of Chrysemys scripta scripta (Schoepff) and an unmarked population of Chrysenigs floridana peninsularis Carr at a north Florida sinkhole pond. The study was conducted between August and December, 1968, thus providing a wide range of environmental temperatures and sunshine in which to obserte any variations in basking behavior.

The number of atmospherically-basking C. s. scripta and C. f peninsularis per day, as well as the number of times individual C s. scripta basked per day, reached a peak at a daily mean water temperature of 28.5°C. Basking decreased during overcast periods. Aquatic basking in C. s. scripta and C. f peninsularis increased as water temperature approached 31.5°C, the maximum mean water temperature recorded during the experimental period. Temperature-telemetry revealed that an adult basking scripta could elevate its body temperature at least 10°C above near-surface water temperatures.

Because of decreased sunshine and air and water temperatures from August to December, and the resultant slower rate of body temperature rise, mean basking duration in C. s. scripta increased during those months. Basking duration is also directly related to body size.

Basking does not appear to be a daily requirement, even under optimum weather conditions. Some C. s. scripta basked up to five times a day in favorable weather; however, a considerable percentage of the population did not bask every day.

Basking activity started about 0800 and reached a daily maximum between 1000 and 1100 each clear day in August and September. The time at which activity started and the time it reached a daily maximum shifted to a later part of the day during October and November.

Thermoregulation appears to be the primary function of the basking act in C. s. scripta and C. f peninsularis. This conclusion is based on the following basking behavioral patterns:

1) body orientatign, head and leg extension and retraction, leg kicking, and rear-foot digit spreading;

2) remaining on a site for considerable periods of time after it becomes shaded and the turtle's body temperature has increased, but rarely emerging at an already shaded site;

3) varying frequency and inversely varying duration with decreasing air and water temperatures and sunshine (shown for C. s. scripta only); and

4) sitting on submerged basking sites or floating in warm surface water.