9301667 Haley Darwin offered "sexual selection" as an explanation for a wide variety of traits having in common the paradoxical quality of being apparently detrimental to survival. He proposed that such traits have evolved because they give an advantage to the bearer in competing for or attracting mates. Sexual selection is now widely regarded to be a major mechanism for the evolution of differences between the sexes and a potentially important factor in the evolution of new species. Yet little is known about the mechanisms underlying sexual selection, the factors constraining it, or the nature of variation in sexually-selected traits. A prerequisite to studying sexual selection is to demonstrate that it operates in the present. Dr. Haley will attempt to obtain such evidence for the long tail feathers of the male streamertail hummingbird (Trochilus polytmus), an endemic Jamaican species. The males of this species have two strikingly long tail feathers (the "streamers"), which are featured prominently in courtship display. Male tail length varies considerably, and the males shed and regrow their tail feathers regularly. To test whether or not females discriminate between males on the basis of tail length, Dr. Haley will perform tests in specially constructed aviaries. Each female will be presented a unique pair of males in an aviary where she can move freely, but each male is confined to a separate adjoining cage. Females will be offered choices between males with experimentally shortened, lengthened, or unaltered tail feathers. If females regularly prefer males with longer streamers, it would seem appropriate to characterize male streamertail tail feathers as sexually-selected traits. If not, future work would include testing male tail length for its effect on competition among males.
