Birds, garden plants and suburban bushlots: where good intentions meet unexpected outcomes

This paper assesses the effects of vegetation retention and garden planting on birds in the rapidly urbanising greater Brisbane region. Formerly forested areas that are cleared and urbanised show a large reduction in the number of small-bodied species, and a minor increase in the number of introduced species. Very small (<5 ha) remnants of eucalypt forest also lose small-bodied native birds, and additionally show increases in larger-bodied species. Suburbs that are better-vegetated resemble the very small remnants: they have not re-acquired small-bodied native species, but have more large species. Analyses of individual species' abundances revealed three distinct species groups. “Aussi Icons” are large-bodied, often ground-feeding species, that characterise well-vegetated suburbs and 1-2 ha remnants of eucalypt forest (“bushlots”). “New Arrivals” are a group of mixed habits that characterise poorly-vegetated suburban areas. “Neglected Foliphiles” are small-bodied, foliage-feeding species that are diverse and common in large eucalypt forest remnants but largely absent from small remnants and well-vegetated suburbs. One species, the noisy miner Manorina melanocephala, is important in aggressively excluding the small foliage-feeding birds from partly-vegetated areas and small bushlots. The abundance of noisy miners was negatively correlated with the number of small-bodied bird species, across all well-vegetated sites, and also within individual types of land cover. Noisy miners occur throughout subtropical and temperate eastern Australia. Planting of scattered eucalypts, small patches, and cultivars of nectar-rich native plant species can encourage noisy miner occupancy, and hence have a different effect on a garden's bird diversity from that intended. I discuss likely avifaunal changes over time, and the implications for land use planning, public education, and spatial scaling in urban design.