AVIAN REPRODUCTIVE TIMING - WHEN SHOULD PARENTS BE PRUDENT

Based on the differing costs and benefits of early breeding, single-brooded parent birds are expected to be prudent, and base their decision to commence breeding on several reliable cues in addition to their energy balance, in contrast to multi-brooded parents. A comparative study using data from supplemental feeding experiments performed on 16 species of birds from 12 genera supported this prediction. The multi-brooded birds advanced their laying dates to a greater extent following food provisioning than the double- and single-brooded birds. The response to food was not affected by female body mass or length of the pre-feeding period, indicating that the differences between species do not simply reflect different metabolic needs of birds differing in size, and that experimental differences in set-up are unlikely to confound the results. Advancement of laying was significantly related to the length of the egg-laying period, but this was mainly due to the strong responses and long breeding seasons of the multi-brooded birds. The results suggest that different birds have different reproductive windows, and some possible factors that might influence the timing of breeding are discussed.