One objective of population biology is to understand how the environment leads to differences among species; another is to explore the behavioral and physiological mechanisms that control life history traits of individual species. This research is designed to contribute to this basic knowledge by studying how hormones shape and direct the life of a small bird, the dark-eyed junco. The focus is on males and the hormone testosterone, which is known to have numerous effects on animal behavior, physiology, and morphology (shape and form). These effects include a suppressive effect of testosterone on male parental behavior and a stimulatory effect on behavior related to mate attraction, e.g. singing. Testosterone can also decrease resistance to disease. By manipulating the amount of testosterone in the blood and comparing the behavior and physiology of the treated birds to that of untreated, control birds, changes induced will be examined and related to correlates of fitness, such as ability to sire offspring, life span, and survival of offspring. The birds will be studied in the field where their survival and success in producing offspring can be monitored. By tracking the fates of animals whose physiology and behavior deviates from the normative state, the research will lead to a more fundamental understanding of how hormonal systems evolve and what balance of selective factors and organismal responses keeps a particular animal species "on track" over evolutionary time.
