Effects of edge type and nest height on predation of artificial nests within subtropical Australian eucalypt forests

Abstract

Elevated levels of predation of birds' nests near forest and woodland edges have frequently been reported for fragmented European and North American habitats, but have not been well tested elsewhere in the world. We used artificial nests to test whether predation was higher at edges within subtropical Australian eucalypt forests. Nine study sites were selected in each of three contexts: forest/pasture edge, forest/suburban edge, and forest interior. Within each site, five artificial nests were placed at each of two heights (ground and elevated), and this experimental design was used for 3 years at interior and suburban edge sites, and 2 years at pasture edge sites. Nests consisted of a grass cup containing one quail egg and two plasticine eggs, and were exposed for 7 days. Effects of edge context, nest height and year were tested using repeated-measures Analysis of Variance. On average, predation levels were about 70% greater adjacent to suburban or pasture edges than within forest interiors, and about 40% greater for ground than elevated nests, and both edge context and nest height were highly statistically significant. Neither year, nor any higher-order interactions, significantly affected predation levels. Predators were identified for 250 of 369 depredated nests, of which 80% had been preyed upon by birds, 12% by mammals, and 7% by reptiles. Our results suggest that birds nesting within eucalypt forests near edges or within small remnant forest patches, which are effectively all "edge", may experience consistently higher predation pressure than birds nesting within interiors of more extensive tracts of forest.