The Use of Co(60) as a Tag for Recovering Amphibians in the Field

Abstract

Students of amphibian and reptile ecology are often vexed by the problem of determining where animals go following periods of observable activity. It is generally known that nearly all amphibian and reptile species retreat underground, but where and how deep are usually unanswered questions. Random excavation of suspected subterranean niches is usually an uncertain procedure. Many of the available data on aestivating or hibernating forms have come from chance observations or when special opportunities present themselves. Cowles (1941) utilized the chance afforded by a land clearing project to gather hibernation data on desert reptiles unearthed by a tractor and scraper. Oliver (1955) reports Latham's observations on Fowler's toad, Bufo woodhousi fowleri, plowed up in fields on Long Island, New York. Many other bits of information are scattered throughout the literature, but the fact remains that critical data on the retreat site and physiological condition of hibernating animals are usually absent from life history studies. Tagging animals with a radioactive isotope and detection with suitable instruments is a relatively new technique which has been used to advantage in field studies of mosquitoes (Hassett and Jenkins 1949; Bugher and Taylor 1949), click beetles (Brian 1947), plovers (Griffin 1952), field voles (Godfrey 1954), and moles (Godfrey 1955). Lachelt (1954) has suggested possible uses of radioactive isotopes in wildlife investigations where the transmission of radioactivity by animals in close association with each other might be used in studying mother-young or prey-predator-scat relationships. The author has been engaged in a study of the natural history of the Yosemite toad, Bufo canorus Camp, a species occupying elevations between 7000 and 1,000 feet in the Sierra Nevada of eastcentral California. In an attempt to recover toads in their subterranean retreats part of a population was tagged with radioactive cobalt during the late spring and summer of 1955. A description of the methods and, problems involved and some of the results are herein reported. Grateful acknowledgment is made of the facilities and detection equipment made available by the Radiation Safety Division, University of California, Berkeley. Horton Steel suggested the use of the radioactive method in tagging amphibians. Special thanks are due Robert Magill, Radiation Safety Engineer, for his helpful advice and active interest in the project. Dr. Robert C. Stebbins and Dr. Oliver P. Pearson kindly read the manuscript and offered valuable suggestions.