The influence of fragment size and edge on nest predation in urban bushland

Abstract

To test the effects of habitat fragmentation and edge on the rate of nest predation in an urban ecosystem, 20 artificial nests each containing 2 plasticine eggs were distributed in each of 24 bushland sites in Sydney, Australia. the eastern yellow robin Eopsaltria australis was adopted as a target species, and variables of nests, eggs and nesting behaviour were manipulated in experiments. Sites ranged in size from 3.8 ha to 14717 ha and were divided into three size classes: 1) 0–10 ha. 2) 11–100 ha and 3) ≥101 ha. Nests were positioned either around the edge of the fragment (within 50 m from the fragment boundary) or within the centre of the fragment (< 50 m from the fragment boundary). The predation rate was calculated as the percentage of nests that had one or both eggs damaged or removed after 15 d of exposure. Nest predation rates were high (average 70.6%) but were not affected by patch size or distance from fragment edges. Predators were identified by marks of the beak or teeth left in the plasticine eggs. Nest predators identified were birds, black rats, brown antechinus and ringtail possum, with the majority of predation being by birds (61.7%), Our findings differ from those of most previous studies of nest predation, and perhaps reflect the ubiquity of generalist predators and the degree of habitat modification throughout remnants of bushland in the urban environment.