The comparative ecology of Australian corvids. IV. Nesting and the rearing of young to independence

Abstract

The five species of Australian Corvus have very similar nesting cycles. Resident species, C. coronoides, C. ovru, and C. tasmanicus, tend to combine the functions of lookout post and nest site and to nest high up overlooking their large territories; the nomads, C. mellori and C. bennetti, are less selective about where they build and may nest close together semi-colonially. Egg characteristics are similar but variable; measurements of four species are similar but C. bennetti has significantly smaller eggs. The nomadic species tend to have smaller clutches, to incubate for less time, and to fledge their nestlings sooner than do the larger resident species. On average a pair of ravens produce about one and a half young per year; figures for crows are less adequate but suggest lower success, C. orru averaging one young per pair over 2 years. Criteria for aging the nestlings visually are given. Growth rates for C. coronoides and C. mellori are similar. In the three species studied only the female incubated and she was fed on the nest by the male; the female also covered the young naked nestlings for most of the first fortnight, after which she shared equally the feeding of young. The young of resident species stay with their parents for several months (C. coronoides 3-4 months), after which they join a passing flock and may wander extensively. Man and wedge-tailed eagles are the chief predators of Australian corvids.