Nest survival drives positive responses of native forest birds to predator management

Back Published 8 November 2024

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It is well known that predation by invasive mammals is the primary threat facing Aotearoa New Zealand (AoNZ)’s remaining native forest birds. Past research by Manaaki Whenua ecologists has demonstrated that distributions of our treasured birds have particularly shrunk in warmer, more northern forests, most likely due to predation pressure being more constant in such places. However, the demographic mechanism – whether failed nesting attempts or lower adult survival – behind such observed declines remains unknown. While research on individual, often most imperilled, species receives most research attention, general mechanisms across the wider bird community are less understood. Such understanding, though, is useful for refining conservation management approaches and to ensure benefits across the bird community, as some species may benefit more than others or some may even be disadvantaged.

Recent research published by Manaaki Whenua ecologists in Biological Conservation sought to address this knowledge gap as part of the MBIE Endeavour-funded project More Birds in the Bush. Researchers used the opportunity presented by AoNZ’s long history of predator management programmes and studies of the demography of forest birds across AoNZ to compile observed demographic rates of native forest birds under different management and temperature gradients in forests.

Their literature review resulted in demographic rates recorded for 26 species, with 5,582 nests monitored and 10,023 adults followed. In total, this represented a staggering amount of fieldwork by hundreds of people from community groups, students, agencies and researchers from different organisations.

Importantly, the analysis showed that across the bird community invasive predator management increases nest survival but not adult survival. Invasive predator suppression and eradication therefore reduces impact on precious native avifauna, and ideally is targeted to coincide with the vulnerable period of nesting. Surprisingly, there was no strong relationship with temperature for either demographic rate despite the known more constant predation pressure in warmer forests. In part this may be due to many of the most imperilled species already only being able to hang on in places with lower predation pressure. AoNZ is similar to other island ecosystems where climate change is likely to exacerbate existing threats such as invasive mammals. Further research tracking the fate of native birds is urgently needed.