Predators and the decline of New Zealand forest birds: An introduction to the hole‐nesting bird and predator programme

Abstract

The role of predators in the decline of New Zealand forest birds, and specifically the roles of mustelids and rodents, is reviewed. Hole-nesting forest birds are particularly vulnerable to predation because they display few predator-avoidance behaviours. Mohua (Molnia ochrocephala) and parakeets are especially at risk because they nest when stoat (Mustela erminea) numbers in the forest are highest, and, because only females incubate, nest predation causes a biassed sex ratio. The Department of Conservation's hole-nesting birds and predator research programme aims to investigate three questions: (1) Are contemporary predators still having a significant impact on the long-term viability of forest bird populations? (2) Can we predict when predators will affect forest bird populations? (3) Can we increase the productivity and viability of forest bird populations by controlling predators? Mohua and yellow-crowned parakeets were used as indicator species to answer these questions, and the resulting eight studies are briefly outlined.

Are low reproductive rates characteristic of New Zealand's native terrestrial birds? Evidence from the allometry of nesting parameters in altricial species

“…Furthermore, gigantism, a trait allometrically related to low rates of reproduction (Livezey 1992), is particularly prevalent in the New Zealand avifauna (Trevelyan & Read 1989;Daugherty et al 1993). Whether the frequency of such features is attributable to environmental saturation is unclear, but the absence of mammalian predators from New Zealand prior to human settlement and the disastrous consequences of their introduction (King & Moors 1979;King 1984;O'Donnell 1996;Holdaway 1999) suggests such a possibility.…”

“…Among altricial, terrestrial birds, hollowand dome-nesting species generally have higher nest success rates, larger clutches, and longer nest (especially nestling) periods than open-nesting species (Kulesza 1990;Martin & Li 1992;Martin 1995). Further investigation of the relationship between nest type and reproductive rates in the New Zealand avifauna may prove profitable because the introduction of mammalian predators has had a marked negative impact on nest success in cavitynesting New Zealand birds (O'Donnell 1996).…”

Relative abundance of mammalian predators in the upper Waitaki Basin, South Island, New Zealand

“…Trapping is an important tool for controlling small mammalian predators in New Zealand (Moller et al 1992;Reed et al 1993;McLennan et al 1996;O'Donnell 1996). As well as protecting valued wildlife, trapping can also provide an index of relative abundance of predators, allowing comparisons of abundance through space and time.…”

The potential for biological control of stoats (Mustela erminea)

“…1996;McLennan etal. 1996;O'Donnell 1996;Wilson et al 1998). Many threatened species continue to decline in the presence of stoats, and some species (e.g., kiwi) are predicted to become extinct within decades unless more cost-effective stoat control is developed.…”

“…Many threatened species continue to decline in the presence of stoats, and some species (e.g., kiwi) are predicted to become extinct within decades unless more cost-effective stoat control is developed. The trapping methods that are currently available for reducing stoat abundance can be applied successfully over reasonably large areas (e.g., up to 6000 ha), but they are too expensive and difficult to implement over larger areas (King 1980;King & McMillan 1982;O'Donnell et al 1996). While recently developed methods of poisoning stoats (Spurr 1998) may have potential for cost-effective control over larger areas (McDonald & Murphy 2000), toxins are becoming less acceptable to the public, especially those that are considered inhumane, are not species-specific, or persist in the environment.…”