Ketterson 97-28384 The primary objective of this research is to explore how the hormone testosterone influences behavior and physiology in a male bird including any effects on a male's ability to survive and reproduce in the wild. The results will enhance understanding of adaptation and constraint and help us to predict how animals respond evolutionarily to changing environments. The Principal Investigators (PIs) treat free-living male dark-eyed juncos (Junco hyemalis, commonly known as the snowbird) with slow-release implants of testosterone (T). Controls receive empty implants. The PIs measure an array of phenotypic traits and compare fitness of the experimental phenotype with that of controls. Only by considering the whole array and the net effect of experimentally induced changes on fitness can they hope to understand what maintains existing harmonal phenotypes. Specific objectives include: 1. continued investigation of direct effects of testosterone on fitness-related traits in male juncos, including a) behavior towards nestlings and b) behavior and physiology during the non-breeding season; 2. quantification of indirect effects of T on the male's extended phenotype by measuring die impact of male T on the behavior and physiology of females (egg steroids, sex of offspring, use of space while fertile); 3. completion of analysis of an already completed l0-year demographic study.
