Influence of food and nest predation on the life histories of two large honeyeaters

Nests of Red Wattlebirds (Anthochaera carunculata) and Noisy Friarbirds (Philemon corniculatus) were watched during four breeding seasons near Armidale, New South Wales (NSW). Friarbirds have larger clutches than Wattlebirds (mode of three v. two) and a shorter breeding season. Two hypotheses (food and nest predation) could explain these differences in life history between the species. We predict that if the food hypothesis is correct Friarbirds would experience a greater seasonal range in food abundance, and hence more abundant food during the breeding season. We also predict that Friarbirds should spend longer incubating, brooding and guarding chicks, because they need to spend less time feeding. If the nest predation hypothesis is correct, Wattlebirds would suffer higher nest predation, and so should spend more time incubating, brooding and guarding their nests, and should visit the nest more synchronously and attack more nest predators. Synchronous visits to the nest reduce the likelihood that predators will be attracted to the nest. We found that Friarbirds spent a greater percentage of time incubating and brooding in the first week after nestlings hatched, and had longer incubation and brooding bouts than Wattlebirds. Wattlebirds left their nests unattended for a greater percentage of the time during incubation, but there was no difference during the nestling stage. There were no differences in the number of incubation bouts per hour, nor in the number of brooding bouts per hour between species. Friarbirds more often visited the nest synchronously during the nestling stage. There was no difference in nest success between the species, with most failures resulting from predation. These results support more of the predictions of the food hypothesis than the nest predation hypothesis. Friarbirds feed themselves and their young on large insects, such as cicadas and scarab beetles, which are abundant for only a short period in the study area, when Friarbird young are dependent. Wattlebirds feed their young on a wide range of insects, including many small ones, which are available over a longer period. The range of clutch-sizes and breeding seasons shown by honeyeaters generally, and friarbirds specifically, provide the opportunity for further testing of these and other hypotheses.