Landscape modification erodes regional distinctiveness in Australian woodland bird assemblages

Rahil Jasminkumar Amin , Jessie C Buettel, Barry W. Brook 

Abstract

Aim: By simplifying habitats and facilitating competitive exclusion, human activities can favour a narrow set of disturbance-tolerant species and homogenise assemblages across regions. We tested how landscape modification and the noisy miner, a hypercompetitive native species, reorganised bird assemblages in southeastern Australia, and whether body size and dispersal capacity predicted species responses.

Location: Southeast Australia.

Time period: January 2020 – February 2026.

Major taxa studied: Terrestrial birds

Methods: We compiled >32 million citizen-science records for 188 bird species across 2,426 sites. We partitioned Jaccard dissimilarity and modelled local contributions to β-diversity (LCBD) along the disturbance gradients. We then tested convergence in β-diversity among biogeographic regions at low and high endpoints of each gradient. We then used joint species distribution and fourth-corner models to link these spatial signatures to species and morphological traits.

Results: Replacement LCBD followed a U-shaped response to agricultural cover, spanning 12.0% between its fitted minimum and maximum. Total LCBD increased by 9.3% from low to high mean woodland patch area, but decreased by 12.0% from low to high woodland cohesion and by 13.8% from low to high noisy miner detection. Between-subregion β-diversity was 0.03–0.07 lower under extensive agriculture, smaller woodland patches, lower woodland cohesion and high noisy miner detection. Agriculture favoured matrix- and edge-adapted, open-country and introduced birds, whereas cohesive woodlands supported more woodland-dependent species. Smaller-bodied species responded more positively to woodland structure, while species with higher hand-wing indices responded more positively to agriculture.

Main conclusions: Across a biogeographically heterogeneous avifauna, landscape modification acted as a recurrent ecological filter, consistently favouring disturbance-tolerant taxa over woodland birds. Repeated losses of woodland birds and gains of disturbance-tolerant taxa erode regional compositional distinctiveness and drive biotic homogenisation. By integrating local β-diversity, direct tests of regional convergence and species-level responses, our analysis reveals how local compositional reorganisation scales up to biogeographic homogenisation and which taxa underpin this pattern.