Abstracts Biological Sciences

Breeding biology and behaviour of the forest raven Corvus tasmanicus in southern Tasmania

by Clare Lawrence

The Forest Raven, Corvus tasmanicus tasmanicus, is the only crow or raven species found on mainland Tasmania. Although members of the genus Corvus have been comprehensively studied, relatively little is known about the Forest Raven. While recently studies have been made of the closely related Northern Forest Raven (C. t. boreus) in New South Wales, this is the first study to be undertaken on the biology of the Forest Raven in Tasmania. Overall, the results of this study suggest that Forest Ravens are similar in their breeding biology and behaviour to other corvid species with similar life-histories, both in Australia and overseas. Adult breeding Forest Ravens maintain large self-sufficient territories year-round. Juvenile ravens remain in these territories with their parents for some months after fledging, before leaving to join nomadic flocks comprising immature birds and non-breeding adults. This study focused on the breeding biology and the behaviour of territory-holding adult Forest Ravens in six territories in light bushland around Hobart, southern Tasmania. Ravens built nests in trees characteristic of the tallest vegetation of the area, nests being situated on average 24m above the ground. The Forest Raven nesting season began in August. Incubation and nestling periods lasted around 22 days and 37-49 days respectively, with second clutches being laid in the event of the failure of the first. Forest Ravens produced on average 1.9 fledglings per pair per nesting season, with most pairs producing two fledglings. The survival rate of fledglings to one month was very high. Away from the nest, and outside the breeding season, Forest Ravens are consistent with other bird species in spending most of their time in perching behaviour and foraging. The Forest Raven is a common and distinctive member of Tasmania's avifauna, and is of commercial importance due to the damage it causes in orchards. Due to the perception of the Forest Raven as an agricultural pest the species is one of only three native bird species not protected by Tasmanian law. In a number of countries corvids are becoming increasingly urban, causing problems through aggressive behaviour, noise and unsanitary mess. Although this has not yet been reported in the Forest Raven, a potential increase in food sources as a result of suburban spread in Tasmania may in the future lead to greater numbers of ravens in such areas. By providing information on the breeding and behaviour of the Forest Raven, the results of this study may be of use in the development of plans or devices to manage the species in a controlled, effective and non-lethal way.