Chelonian Conservation and Biology, 2003, 4(3):569–577 © 2003 by Chelonian Research Foundation
Activity and Thermal Ecology of the Box Turtle, Terrapene ornata, at its Southwestern Range Limit in Arizona MICHAEL V. PLUMMER1
Department of Biology, Box 12251, Harding University, Searcy, Arkansas 72149 USA [E-mail:firstname.lastname@example.org; Fax: 501-279-4706]
ABSTRACT. – Activity and thermal ecology of Terrapene ornata luteola were studied in southeastern Arizona, near the extreme southwestern range limit for T. ornata, using a combination of radiotransmitters and temperature data loggers attached to individual turtles. Surface activity was greatly affected by rainfall and operative temperatures both seasonally and daily. Mostof the annual activity occurred in a 90-d period from July through September coincident with monsoon rains. On a daily basis, turtles exhibited two periods of surface activity, a 3 hr period in early morning and a 1.5 hr period in late afternoon. Precipitation enhanced both daily and seasonal activity. Burrows of the kangaroo rat, Dipodomys spectabilis, provided the most important subterraneanrefuge. The observed patterns of daily activity, field body temperatures, and laboratory preferred body temperatures in Arizona were similar to those of most other populations of T. ornata that have been studied across the species’ range, with the exception of extreme northern populations in Wisconsin and Nebraska. Compared to populations of T. ornata in the central portions of the species’ range,there is no clear evidence of adjustments in either behavioral microhabitat use, thermoregulatory set point temperatures, or field body temperatures at the species’ southwestern range limits. Broad thermal tolerances and an ability to behaviorally adjust both daily and seasonal activity times opportunistically may permit the existence of T. ornata luteola at its southwestern range margin in Arizonawhere hydric and thermal factors might be expected to constrain a primarily prairieadapted species. KEY WORDS. – Reptilia; Testudines; Emydidae; Terrapene ornata luteola; turtle; activity; thermoregulation; body temperature; operative temperature; terrestrial; range limits; geographic variation; Arizona; USA Reptiles commonly respond to variation in environmental heat loads by relying onbehavioral modifications such as changing microhabitats or times of activity (e.g., Hertz and Huey, 1981; Christian et al., 1983). However, when heat load variation is extreme, behavioral changes may not provide essential thermal requirements or be too costly in terms of the time and energy expended in the behavior (Huey and Slatkin, 1976). In such cases, microhabitat or activity adjustments may beenhanced by altering thermoregulatory set point temperatures. For example, in Wisconsin the wide-ranging box turtle Terrapene ornata responds to lower heat loads by modifying its behavior and lowering its set point temperatures compared to T. ornata from Kansas (Ellner and Karasov, 1993). Terrapene ornata is a prairie species ranging from southern Wisconsin to Louisiana west to southeast Wyoming andsoutheast Arizona and extending south into south Texas, northern Sonora, and northern Chihuahua (Conant and Collins, 1991). Four decades ago, Legler (1960) suggested that the most favorable environments and densest populations occurred in the central portions of the species’ range in Kansas, Nebraska, Oklahoma, and northern Texas. The general ecology of T. ornata has been investigated to variousdegrees in Wisconsin (Doroff and Keith, 1990), Kansas (Legler, 1960; Metcalf and Metcalf, 1970), central Texas (Blair, 1976), and New Mexico (Norris and Zweifel, 1950; Nieuwolt, 1993, 1996; Nieuwolt-Dacanay, 1997). Relatively little research has targeted populations near the southwestern limits of the species’ range; the westernmost limit being an intergrade population (T. o. ornata x T. o. luteola)...