Seasonal Variations in Plasma Testosterone Level in Male Eastern Wild Turkeys

Abstract

Testosterone level was determined, by radioimmunoassay, on 137 plasma samples obtained from male eastern wild turkeys (Meleagris gallopavo) over a 15-month period, in Alabama. Ninety-three samples were obtained from 3 pen-reared birds by making collections every 2 weeks for 62 consecutive weeks; 14 samples were from trapped birds; and 30 were from gobblers killed during the regular spring hunting season. Plasma testosterone levels for pen-reared birds at 6 weeks of age (July 1974) were 3263 ng/100 ml; whereas those at 34 weeks of age (January 1975) and just prior to breeding season were 87-108 ng/100 ml. Mean plasma testosterone level in January-February for the mostly adult trapped birds was 202.2 ? 61.9 ng/100 ml compared to 146.0 ? 62.3 ng/100 ml for the subadult pen-reared birds. Values for the mostly adult gobblers killed during the March-April hunting season was 344.9 -+110.8 ng/100 ml compared to 254.4 _ 140.5 ng/100 ml for the subadult pen-reared turkeys. Changes in behavior and body conformation in relation to changes in plasma testosterone level are discussed for the three pen-reared turkeys. J. WILDL. MANAGE. 41(2):784-188 Knowledge of the seasonal variations in sex hormone level in male eastern wild turkeys is important for a more precise delineation of the bird's breeding season, and also for a better understanding of its behavioral and anatomical changes. This information can be useful to game managers as an additional tool for evaluating reproductive status in wild populations. Information regarding the seasonal variations in plasma testosterone levels in either wild or domestic turkeys is lacking. Furthermore, no specific value for plasma testosterone level has been reported for males of either wild or domestic turkeys. In a brief abstract, Zimmerman and Wentworth (1974) reported that they had measured the serum testosterone level in large white domestic turkeys in response to changes in photoperiod; however, they gave no specific data. Arcos (1975) reported the isolation of testosterone from the ovarian blood of the laying turkey but did not quantify the level. Plasma testosterone level for the male domestic fowl has been reported as 84-783 ng/100 ml (Furr and Thomas 1970) and for the mallard (Anas platyrhynchos) as 65-270 ng/100 ml by Jallageas and Attal (1968, cited by Bell and Freeman 1971). Changes in the circulating level of the androgens, and more specifically testostero e, are responsible for changes in male secondary sex characteristics in most vertebrates. These may include cyclic or acyclic changes in body color, body conformation, vocalization, breeding condition and sexual b havior (Turner and Bagnara 1971). Male eastern wild turkeys exhibit both behavioral and anatomical changes during their breeding season. Birds become belligerent toward other males, and courtship display toward females becomes active. Seasonal changes in body conformation include increased brilliance of facial color in caruncles and throat wattle, and the development of a large fatty breast sponge. All of these changes presumably are related to changes in the circulating levels of androgens, particularly testosterone. We wish to thank W. H. Hamrick, Wildlife Biologist, Alabama Department of Conservation, and J. R. Gwaltney, research 184 J. Wildl. Manage. 41(2):1977 This content downloaded from 157.55.39.243 on Thu, 06 Oct 2016 04:56:19 UTC All use subject to http://about.jstor.org/terms SEASONAL VARIATIONS IN WILD TURKEY TESTOSTERONE ? Lisano and Kennamer 185 assistant, Auburn University, for their assistance in obtaining blood samples. We are also grateful for the technical assistance of H. E. Whatley, graduate assistant, Auburn University, in the determination of plasma testosterone levels. MATERIALS AND METHODS