Birds and insects respond differently to combinations of semi-natural features in farm landscapes

Semi-natural features among farmland have a key role in maintaining wildlife in rural landscapes. Practical conservation requires knowledge of which combinations of features are of greatest value and whether this differs among faunal groups. We used a 'landscape' approach to investigate the relative importance to birds and insects (bees, flies, wasps) of combinations of three wooded features typical of farmland in south-eastern Australia: scattered trees, wooded roadsides and wooded streamside vegetation. We selected 44 landscapes (1 km diameter) representing four combinations: a) landscapes with all three features present, b) landscapes lacking scattered trees, c) lacking wooded roadsides, and d) lacking wooded streamsides. We surveyed birds and selected insects, and compared mean alpha (α, site), beta (β, between site) and gamma (γ, landscape) diversity for each taxon between landscape types; and gamma (γ) diversity of bird species displaying breeding activity. Mean α-diversity of birds was reduced in landscapes lacking wooded roadsides or streams, relative to those with all three wooded features; while species differentiation (β-diversity) increased in these landscapes. Loss of streamside vegetation had the greatest landscape-scale impact, reducing γ-diversity by ~33% for all land-birds and ~50% for woodland birds. Bird breeding activity declined by ~50% in landscapes lacking wooded streamsides. In contrast, insects showed little response, except bees for which mean α-diversity was greater in more-open landscapes lacking scattered trees or wooded roadsides, compared with those containing all wooded features. This did not lead to differences in landscape-level (γ) diversity. Synthesis and applications. Marked differences in how birds and insects respond to different combinations of semi-natural features mean that a 'one size fits all' approach to nature conservation is insufficient. Wooded features, especially streamside vegetation, are critical for maintaining diversity and breeding activity of woodland birds. In the absence of adequate knowledge of many insect groups in southern Australia, a prudent approach is to foster a diverse farmland mosaic comprising semi-natural habitats together with floristically rich, modified features that provide temporally dynamic resources. Small semi-natural features have disproportionate value for conservation, relative to their area, while also benefitting farm productivity and supporting ecosystem services.