Woodland fragmentation is causing the decline of species and functional groups of birds in southeastern Australia JAMES WATSOW·, ALEXANDER WATSOW , DAVID PAULVand DAVID FREUDENBERGER4 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. Key words: Birds, Foraging guilds, Woodland fragmentation, Habitat complexity, southeastern Australia. INTRODUCTION VAST areas of Australia's temperate woodlands have been removed since European settlement, with as little as 3% of some ecosystems remaining (Yates and Hobbs 1997). Woodland ecosystems now typically consist of remnant patches set in a highly altered landscape matrix. These woodland remnants provide core habitat for a unique, diverse and endemic avifauna. The scale of fragmentation and level of disturbance have resulted in woodland birds being the most adversely affected group of Australia's avifauna (Robinson and Traill 1996; Reid in litt 1999; Garnett and Crowley 2000). Trends towards local extinction, reduced avian diversity and increased community homogenization appear to be accelerating despite the fact that, in most regions temperate woodland clearance has slowed significantly (Saunders 1989; Smith et al. 1996; Recher 1999; Major et al. 2001). To prevent further declines in woodland birds, substantial effort is being directed towards rehabilitation and restoration projects. Recent publications have provided ecological guidelines and principles for managing native vegetation in order to conserve native bird species (Hobbs and Saunders 1991; Barrett et al. 1994; Bowers 1998; Dale et al. 2000; Garnett and Crowley 2000; Major et al. 2001; Watson et al. 2001). Current restoration and rehabilitation programs aim to increase the size and habitat complexity of existing remnants. This is because both remnant size (Ford et al. 1995; Watson 1999; Siversten and Clarke 2000; Zanette et al. 2000; Major et al. 2001) and habitat complexity (Gilmore 1985; Arnold 1988; Garnett 1992; Lambeck 1997; Canterbury et al. 2000; Ludwig et al. 2000; Watson et al. 2001), have been shown to affect avifaunal communities throughout Australia. This paper describes how resident woodland bird assemblages respond to variations in remnant patch size and vegetation structural complexity in the northern Australian Capital Territory and bordering areas of New South Wales. Furthermore, it assesses how bird foraging guilds respond to these variations. The results of this study are important because they identify the types of birds that are likely to 'Biodiversity Research Group. School of Geography and the Environment. University of Oxford. Mansfield Road. Oxford. OXI 3TB. United Kingdom. 'Centre for Ecosystem Management. Edith Cowan University. 100 Joondalup Drive. Perth. Western Australia. Australia 6027. 'School of Geography and Oceanography. University College. University of New Wales. Australian Defence Force Academy. Northcott Drive. Canberra, Australian Capital Territory. Australia 2600. 'CSIRO Sustainable Ecosystems. GPO Box 284. Canberra. Australian Capital Territory. Australia 2601. ·Corresponding author. PACIFIC CONSERVATION BIOLOGY Vol. 8: 261-70 Surrey Beatty &: Sons. Sydney. 2003.