Visual and nutritional food cues fine-tune timing of reproduction in a neotropical rainforest bird

Food may act as a proximate factor in the regulation of avian seasonal bree ding. Food cues could provide particularly important seasonal information t o birds living in variable tropical environments, but this has not yet been tested. Spotted antbirds (Hylophylax n. naevioides) inhabiting a humid for est in central Panama (9 degrees N) Likely use changes in the tropical phot operiod to time reproduction on a long-term, seasonal basis. We predicted t hat these insectivorous birds also adjust reproduction to short-term cues s uch as food availability because the onset of the rainy season and the resu lting increase in insect abundance varies considerably between years. To te st this prediction, prior to their breeding season (when they had half-maxi mal gonads), we either exposed captive male spotted antbirds to an ad libit um standard diet only or added live crickets to this diet. Males that recei ved live crickets significantly increased gonad sizes within 3 weeks over c ontrols on the standard diet. Moreover, in six additional experiments crick et availability always increased song rate, usually within a few days. The stimulatory effect of live crickets on song activity may function independe nt of nutritional aspects: Freshly killed crickets, providing similar nutri tional content as live crickets, did not stimulate the birds' song activity . However, song activity increased to intermediate levels when live cricket s were shown under a clear plastic wrap, i.e., when birds could see but not eat crickets. We hypothesize that the opportunity to see and handle live i nsects stimulates song and reproductive activity in these birds. Our data i ndicate for the first time that a tropical rainforest bird can use food cue s to evaluate the suitability of local environmental conditions for breedin g. (C) 2000 Wiley-Liss, Inc.