Comparison of foraging behaviour of small, urban-sensitive insectivores in continuous woodland and woodland remnants in a suburban landscape

Abstract

Small patches of remnant vegetation are often considered to have low conservation value. In urban landscapes their value may potentially be higher than in other landscapes because they can be the only representatives of original native vegetation. Despite this potential, many small insectivorous birds that rely on native vegetation demonstrate sensitivities within urban landscapes through reduced numbers or total absence. One reason for this sensitivity may be that remnants are of suboptimal quality, which may be reflected in behavioural changes. Using five insectivorous species that were present (in low numbers) in remnants surrounded by high-density housing, foraging behaviour was examined in relation to vegetation. The proportion of time birds spent on different foraging substrates and plant species was compared with that of conspecifics in continuous vegetation. Canopy and shrub foragers showed minimal behavioural changes. Ground foragers in remnants tended to forage at lower heights than those in continuous vegetation; however, these changes did not appear to reflect a negative effect. These changes were partially explained by structural differences between vegetation in remnants and continuous sites. The number of times a bird attacked prey items was significantly higher in continuous habitat for only two species. Overall, the foraging behaviour of small insectivorous birds in remnants surrounded by high-density housing was not adversely affected by urbanisation and it appears that remnants have potential value as habitat and foraging sources in an urban landscape. Despite this, small insectivores are still sensitive to urbanisation, suggesting that other factors, probably in the matrix, are important.