Thermoregulation of the American Alligator, Alligator mississippiensis

Despite the substantial literature concerning behavioral and physiological thermoregulation of reptiles, the crocodilians have received little attention. Aside from the study by Colbert, Cowles, and Bogert (1946) in which they determined the preferred (32-35 C) and lethal temperatures (38-39 C), little is known about the temperature ecology of the American alligator. Cott (1961) observed thermoregulatory behavior in Crocodilus niloticus and concluded that they exert considerable control over their body temperature by behavior. Most of the available data for the crocodilian group consist of isolated field measurements of body temperature (Brattstrom 1965) which are difficult to place into a meaningful biological context. Spotila, Soule, and Gates (1972) have constructed a mathematical model for the heat energy budget and climate space of the alligator and have extended it to modeling the body temperatures of larger reptiles (Spotila et al. 1973). They predicted a relatively stable body temperature for large reptiles due mostly to thermal lag and heat storage. Using radio telemetry to measure body temperature of captive alligators, Spotila (1973) found the alligator could increase its body temperature by basking. It was further shown that by using water as a heat sink alligators 1 Portions of this paper were part of a thesis submitted in partial fulfillment of the requirements for the M.S. degree at Baylor University, Waco, Texas. Obviously this research could not have been completed without the help of many people and several agencies. Dr. Eugene Crowder, Baylor University, now deceased, directed the study. Dr. Frederick Gehlbach, Baylor University, outlined the study and secured major funding from the National Geographic Society. Dr. Robert Allison, Scott and White Clinic, Temple, Texas, and Dr. Sara Huggins, Baylor School of Medicine, Houston, Texas, aided in the development of surgical technique. Mr. Jim Pittello, acting director of the Cen-Tex Zoo, Waco, Texas, provided zoo facilities and consented to the use (at considerable risk) of one of the zoo alligators. Mr. Ted Joanen, director, and Larry McNease, of the Rockefeller Wildlife Refuge, Grand Chenier, Louisiana, introduced me to the proper ways of collecting, handling, sexing, and marking alligators and generously shared unpublished data. Dr. Clarence Cottam, director, now deceased, and Mr. W. C. Glazener, assistant director, provided time, equipment, and excellent accommodations for field portions of the work at the Rob and Bessie Welder Wildlife Foundation, Sinton, Texas. Mr. Robert L. Cross and others at the Texas Parks and Wildlife Department provided advice and permits for collecting and holding the alligators. Mrs. Opal Smith, now deceased, assisted in the preparation of artwork, and my wife, Joan, helped in typing, table layout, and statistical analysis. Miss Nancy Perry and Miss Nancy Ekholm aided in data acquisition, processing, and testing of the telemetry system. Mr. Gene Keepers assisted, often without pay, in the field and laboratory measurements. Financial support was provided by the following grants: NSF University Grant to Baylor University; Baylor University Grant; a grant from the National Geographic Society to Dr. Frederick R. Gehlbach; and a Sigma Xi grant to the author. Drs. Frederick Gehlbach, Francis Rose (Texas Tech University) and Joseph O'Brian (Texas Tech University) critically read the manuscript. However, I am responsible for the content. 2 Present address: Department of Biology, Texas Tech University, P. O. Box 4149, Lubbock, Texas 79409.