Responses of New Zealand forest birds to management of introduced mammals

What is it about?

Large-bodied, deeply endemic forest birds benefit most from control of introduced predatory mammals. The management history of New Zealand's forests over the past 50 years, with varied levels of mammalian predator control, has created, in effect, a replicated management experiment. We conducted a meta‐analysis of population‐level responses of forest birds to different levels of mammal control recorded across New Zealand. We collected data from 32 uniquely treated sites and 20 extant bird species representing a total of 247 population responses to 3 intensities of invasive mammal control (zero, low, and high). The treatments varied from eradication of invasive mammals via ground‐based techniques to periodic suppression of mammals via aerially sown toxin. We modeled population‐level responses of birds according to key life history attributes to determine the biological processes that influence species’ responses to management. Large endemic species, such as the Kaka and New Zealand Pigeon (Kereru), responded positively at the population level to mammal control in 61 of 77 cases for species ≥20 g compared with 31 positive responses from 78 cases for species <20 g. The Fantail and Grey Warbler, both shallow endemic species, and 4 nonendemic species (Blackbird, Chaffinch, Dunnock, and Silvereye) that arrived in New Zealand in the last 200 years tended to have slight negative or neutral responses to mammal control (59 of 77 cases). Our results suggest that large, deeply endemic forest birds, especially cavity nesters, are most at risk of further decline in the absence of mammal control and, conversely suggest that 6 species apparently tolerate the presence of invasive mammals and may be sensitive to competition from larger endemic birds.

Featured Image

Photo by Andrea Lightfoot on Unsplash

Photo by Andrea Lightfoot on Unsplash

Why is it important?

Over the past 1000 years New Zealand has lost 40–50% of its bird species, and over half of these extinctions are attributable to predation by introduced mammals. Populations of many extant forest bird species continue to be predated upon by mammals, especially rats, possums, and mustelids (e.g. stoats). This work demonstrates a clear link between the intensity of mammal control and which types of bird species are likely to benefit, and by how much. It also provides an evolutionary perspective on vulnerability to predation.