Density of Birds in Eucalypt Woodland Affected to Varying Degrees by Dieback

Abstract

Birds were censused in four sites near Armidale, NSW. One area of healthy eucalypt woodland had twenty-three and twenty-one birds per hectare in censuses during July-September 1978 and August-December 1979. One site, suffering a moderate degree of 'eucalypt dieback', had about ten buds per hectare. Another site with severe dieback had just over two birds per hectare, and open grassland less than one bird per hectare. These three sites were censused in 1979. The estimated energy requirements of the buds were similar in healthy and moderately affected sites but reduced to forty and ten per cent of those in the healthy site in severely affected woodland, and grassland. Small insectivorous birds disappeared most rapidly as trees declined in health whereas larger birds were less severely affected. Australian Magpies and Eastern Rosellas were most abundant in the moderately and severely affected sites. Loss of cover specially in the understorey, which resulted in greater exposure of the nests of small birds to predation and weather, was probably the main reason for losses of small insectivorous birds. To establish diverse bird communities and probably healthy woodland on the New England Tablelands, areas ought to be fenced to prevent grazing and to allow a shrub layer to develop.