Woodland fragmentation is causing the decline of species and functional groups of birds in southeastern Australia

Abstract

The clearance of woodlands and the simultaneous creation of alien environments have been identified as the primary reasons for the decline of many woodland birds in southeastern Australia. This study measured how the size of woodland remnants and habitat structural complexity affected bird composition and distribution in the northern Australian Capital Territory and bordering areas of New South Wales. Within this region only 8% of the original woodlands remain, embedded as patches in a matrix of pasture and suburbia. Woodland birds were surveyed in 72 woodland remnants of different size and vegetation structural complexity. Avifaunal species richness was found to increase with remnant area and habitat complexity (p < 0.01). Of the 31 resident woodland bird species detected, 22 were significantly affected by woodland patch size reduction and 20 species were significantly affected by habitat complexity loss (p < 0.05). Of the species affected, 19 were affected by both reductions in patch size and vegetation complexity. Seven species (Weebill, Brown Thornbill, Buff-rumped Thornbill, Spotted Pardalote, Grey Shrike-thrush, Scarlet Robin and White-winged Chough) not previously identified as threatened by habitat fragmentation occurred significantly less often in small remnants with low habitat complexity. Assessment of avifaunal guilds based on body size and foraging behaviour showed that all large species (n = 4) and 85% (n = 17) of insectivorous species that foraged above the ground were statistically affected by patch size and/or loss of habitat complexity. The occurrence of three species (50%) of granivores was also significantly affected (p < 0.05) by patch size and/or habitat complexity reduction. These results show that the distribution of many bird species, including some considered "common" and "widespread", is affected by patch size and habitat complexity. There are few, large complex woodland remnants within the study area, which continue to reduce in size and complexity. It is therefore predicted that the decline of woodland bird species will continue unless appropriate habitat conservation strategies are applied.