The vocal communication system of birds has long served as a model system for the study of vocal communication in general. One reason is that the behavior of birds is especially easy to study. Another reason is that avian vocal communication has so many similarities to human communication, for example, in development and in neural control. Progress in studying the function of avian vocal signals has recently been aided greatly by the use of a bioassay for measuring preferences of female birds for male vocalizations. In this bioassay, captive females are first treated with a hormone, estradiol, and then exposed to playback of recorded vocalizations. Females respond to appropriate vocalizations with a courtship display, which is used as the response measure. Dr. Searcy will investigate the hormonal basis of the bioassay by treating females with different doses of estradiol, measuring levels of the hormone in their blood, and relating dose and blood level to their degree of responsiveness to vocal stimuli. These experiments should both advance our understanding of the hormonal control of reproductive behavior in female birds and lead to methodological improvements in the bioassay for female vocal preferences. In a second series of experiments, Dr. Searcy will test the effect of loudness of vocalizations on female preferences. Based on other investigators' experiments with frogs, theories have been proposed to explain why some preferences can be reversed by changing loudness while others are insensitive to such changes. Dr. Searcy will test whether or not these theories can be extended to birds, as a step towards unifying the field of bioacoustics. In a third set of experiments, Dr. Searcy will test the ability of female birds to sort vocalizations produced by different males, using a technique similar to experiments on people's discrimination of unfamiliar voices. These experiments will provide another step towards producing theories of vocal communication that are general across all animals, rather than specific to just one group.
