Functional group‐dependent responses of forest bird communities to invasive predator control and habitat fragmentation

Abstract

Aim Mounting global pressure on bird populations from invasive predators and habitat loss has driven a rapid growth in restoration and conservation action around the world, yet the efficacy of such actions is still not well understood. We investigated the relative and interactive effects of invasive predator control and habitat fragmentation on the abundance of native birds and invasive mammalian predators in native forest fragments.

Location Waikato region, New Zealand.

Methods We sampled invasive mammalian predator and native bird abundances using camera traps and bird counts at 26 sites in 15 forest fragments across New Zealand's Waikato region. Fragment area, shape complexity and surrounding land cover of exotic and native forest were determined in ArcMap. We further created two composite gradients reflecting predator control intensity and temporal distribution of control based on seven quantitative variables recorded in each of the 5 years preceding data collection. Finally, we estimated the relative influence of these drivers on invasive mammals and functional groups of native birds using model averaging.

Results Both the intensity and temporal distribution of invasive predator control significantly affected invasive predator abundance. Landscape and fragment structure were often equally important drivers of invasive predator abundances, but responses varied among invasive mammal species. Both invasive predator control intensity and fragment structure were similarly important drivers of native bird abundance, though bird community responses varied markedly between functional groups.

Main conclusions Our findings suggest that spatial extent of invasive predator control and fragment area constrain invasive predator numbers and enhance bird abundance, especially for small insectivorous species, whilst other aspects of habitat fragmentation are less important for invasive mammals but at least as important for native bird communities. Consequently, both drivers should be given strong consideration when undertaking landscape-scale conservation and restoration of bird communities in human-altered landscapes threatened by invasive predators.