68.2 Saturday, Jan. 5 Comparing the effects of testosterone treatment on onset and continuity of plumage molt between two species of cardueline finch BRAZEAL, KR*; HAHN, TP; UC Davis; UC Davis email@example.com
All birds must replace their feathers each year in order to survive, but species vary in their flexibility of timing the transition from breeding to molt. Past studies have established that high levels of sex steroids (e.g. estradiol and testosterone associated with breeding) can delay the onset of molt. Differing responsiveness to sex steroids may be responsible for variation in molt timing among species. This study compared the role of testosterone in regulating molt timing in two species of cardueline finches. House finches and pine siskins are both seasonal breeders, but the latter are considered more flexible in their reproductive timing because they will sometimes arrest their molt if conditions become favorable for late summer breeding. Wild caught birds of both species were brought into captivity and treated with testosterone via silastic implants administered either prior to molt or during the middle of molt. We found that pine siskins were more sensitive to testosterone than house finches; testosterone completely prohibited molt in the siskins until the implants were removed, while many of the house finches were able to slowly molt a limited number of feathers during the treatment period. However, house finches given testosterone during the middle of molt arrested molt more abruptly than did pine siskins. These results help to clarify mechanisms by which different species coordinate transitions from one life cycle stage to the next.