This proposal addresses the evolution of male reproductive behavior in birds. In general, male vertebrates mate promiscuously and provide little help in rearing offspring. However, males are usually monogamous and they often provide care to their young. It has long been assumed that monogamy and parental care evolved in birds because male care was necessary for the successful rearing of offspring. Recent research, however, has shown that female birds whose mates have been taken from them are often able to comensate for mate absence. Other recent research has examined the hormonal basis of mating and parental care behaviors in birds. By manipulation of male physiology through testosterone implants, workers have found that increased testosterone leads to both an increase in the tendency for males to mate polygynously and a decrease in their tendency to care for offspring. If females are able to rear young without male help and if polygyny requires only a relatively small physiological alteration, then the question arises, why has male care evolved and what constrains males to monogamy? This proposal is designed to answer this question; it proposes an alternative explanation for male monogamy and a test of this explanation. Ketterson and Nolan will treat males with testosterone and attempt to quantify any effect of testosterone-altered behavior on male survivorship. They will then observe the responses of females toward males, in particular any tendencies to mate initially with altered males and to maintain or not to maintain the association over the course of the full breeding season. Their results should contribute to our general understanding of the evolution of behavior by permitting a quantitative estimate of costs and benefits associated with alternative reproductive physiologies. One potential applied aspect of this work is the greater insight into the evolution and regulation of human parenting behavior it may provide. Divorce is common in our society and the costs to children are high. Human males differ from most other mammals in the extent to which they provide parental care to their young; their behavior more closely resembles that of birds than the most commonly studied mammal, the rat. Although it is always risky to draw comparisons between human behavior and that of other animals, it is also true that an increased understanding of the physiological and ecological basis for mating and parental behavior may help society take a more objective look at its own behavior. Because of the scarcity of mammal models for male parental care, birds may provide the best alternative.
