The comparative ecology of Australian corvids. II. Social organization and behaviour

Abstract

For five species of morphologically very similar Corvus to occur on one continent and for two or three of these species to frequently coexist in sympatry, effective isolating mechanisms must be active to maintain species integrity. This paper describes and compares the behaviour and social organization of Corvus coronoides and C. mellori in detail; C. tasmanicus, C. orru, and C. bennetti were studied less intensively but are compared wherever possible. Few spectacular or species-specific displays were recorded. Calls are varied and a "vocabulary" for C. coronoides is given; each species has a characteristic territorial advertisement call. Both C. coronoides and C. mellovi form long-lasting pair bonds; probably the other species do so as well. Adults of C. coronoides, C. orru, and C. tasmanicus maintain territories all the year round; immatures and non-breeding adults live in nomadic flocks. C. mellori and C. bennetti occupy a breeding territory only for the minimum time (3 months) necessary to rear young; for the rest of the year they and their non-breeding conspecifics are nomadic. The number and size of C. covolzoides territories varied little over the years of the study; this and the ever-present reservoir of mature but non-breeding adults in the flocks suggest that large mosaic territories for permanently resident species may limit breeding density. The nomadism of non-breeding birds enables transient localized food-gluts to be utilized.