Bird declines over 22 years in forest remnants in southeastern Australia: Evidence of faunal relaxation?

Abstract

Declines in Australia's forest avifauna are largely attributed to loss of native vegetation. Many studies have examined patches of remnant vegetation, but few have considered changes over many years. In our study, bird data were collected 22 years apart (survey period A (SPA), 1980–1983; survey period B (SPB), 2002–2005) in 20 forest remnants in a rural landscape in southeastern Australia. Initial modelling (SPA) predicted a decline of nine species per patch in the 100 years following fragmentation. Our data showed that average species richness declined by nine species per patch in just 22 years between SPA and SPB, perhaps representing an example of faunal relaxation. Observer variation, changes in climate, changes in land use, and interspecific competition from an aggressive edge-adapted native bird (the noisy miner, Manorina melanocephala (Latham, 1802)) did not appear to be the main drivers of this decline. However, noisy miners were strongly associated with high turnover of forest species where they occurred above a threshold of six birds per count. Revisiting sites after an interval of many years has shed new light on the dynamics of a fragmented ecosystem, and indicates that further bird declines are likely as a result of past habitat loss.