Effects of habitat transitions on rainforest bird communities across an anthropogenic landscape mosaic

We compared bird community responses to the habitat transitions of:
rainforest-to-pasture conversion, consequent habitat fragmentation, and
post-agricultural regeneration, across a landscape mosaic of about 600
km2 in the eastern Australian subtropics. Birds were surveyed in
seven habitats: continuous mature rainforest; two size-classes of mature
rainforest fragment (4-21 ha, 1-3 ha); regrowth forest patches dominated
by a non-native tree (2-20 ha, 30-50 years old); two types of isolated
mature trees in pasture; and treeless pasture; with six sites per habitat.
We compared the avifauna among habitats, and among sites, at the levels of
species, functional guilds, and community-wide. Community-wide species
richness and abundance of birds in pasture sites were about one-fifth and
one-third, respectively, of their values in mature rainforest
(irrespective of patch size). Many measured attributes changed
progressively across a gradient of increased habitat simplification.
Rainforest specialists became less common and less diverse with decreased
habitat patch size and vegetation maturity. However, even rainforest
fragments of 1-3 ha supported about half of these species. Forest
generalist species were largely insensitive to patch size and successional
stage. Few species reached their greatest abundance in either small
rainforest fragments or regrowth. All pastures were dominated by bird
species whose typical native habitats were grassland, wetland and open
eucalypt forest, while pasture trees modestly enhanced local bird
communities. Overall, even small scattered patches of mature and regrowth
forest contributed substantial bird diversity to local landscapes.
Therefore, maximising the aggregate rainforest area is a useful regional
conservation strategy.