Breeding biology of rainbow bee-eaters (Merops ornatus): A migratory, colonial, cooperative bird

The breeding biology of Rainbow Bee-eaters (Merops ornatus) was studied between 1997 and 2001 in southeast Queensland, Australia. Rainbow Bee-eaters are unusual in that they combine migration and coloniality with cooperative breeding. Birds migrate from islands north of Australia to build nests either solitarily or in colonies containing ≤50 active nests that are attended by socially monogamous pairs or trios (45% of nests). Nesting was essentially forsaken during very dry seasons, whereas hatching success was reduced in wet seasons. Incubation period varied in duration, with chicks emerging 22-31 days after incubation commenced. Eggs hatched either synchronously or, more commonly, asynchronously (88% of clutches), with each chick emerging usually 0-3 days after the previous hatchling in the nest. Asynchronous hatching typically led to a marked size hierarchy within the brood, facilitating starvation of 22% of nestlings that had avoided nest disasters, such as predation or flooding. Duration of the nestling period was also variable, with chicks requiring a further 24-36 days to fledge. Nest predation by native predators - monitor lizards (Varanus varius) and yellow-footed antechinus (Antechinus flavipes) - was relatively low, affecting 10% of nests. In contrast, predation by two introduced species - dingoes (Canis familiaris dingo) and, in particular, cane toads (Bufo marinus) - was extreme, terminating 49% of all nests.