Good predators: the roles of weka (Gallirallus australis) in New Zealand’s past and present ecosystems

Abstract

There is increasing interest in restoring native predators in order to regulate ecosystems and maintain biodiversity, but predator reintroductions are still controversial for complex social and ecological reasons. Few studies have examined predator restoration on islands or in ecosanctuaries, where highly endemic faunas have typically undergone precipitous declines and extinctions due to novel invasive predators, and translocations are used to restore species. Currently in New Zealand, discussions regarding predators typically focus on introduced mammalian pests, and the importance of native predators is frequently overlooked. We present a case study of the mesopredatory New Zealand weka (Gallirallus australis), a threatened flightless rail that provokes controversy among restoration practitioners due to concerns that it may decrease populations of other threatened species. We (1) review studies of weka diet and impacts on native and exotic fauna; (2) contrast prehistoric and contemporary predation webs focused on weka; and (3) consider the role of biocultural approaches in the management and restoration of socio-ecological systems with weka. Weka are opportunistic omnivores that can include vertebrates in their diet, and on small islands where weka can reach high densities there is some evidence that they may limit some prey populations. However, very few manipulative experimental studies measuring effects of weka on native species have been carried out, and such studies would be extremely valuable. Weka also consume invasive rodents and, if they obtain a sufficiently high density, may provide benefits in ecosanctuaries by limiting invasive mice populations. Māori historically harvested weka, and such harvest may now valuably limit weka numbers at certain island or ecosanctuary sites, perhaps replacing the effect of extinct avian competitors and apex predators. How weka and other native predators should be managed on islands depends on the value placed on ecosystem restoration, species-focused conservation, or biocultural enrichment.

A trial on Te Pākeka/Maud Island for reducing aerial baiting sow-rates for the eradication of house mice

“…Significant numbers of weka were functionally eradicated in line with the island's management to protect endangered herpetofauna and invertebrate species, and to eliminate interference with biosecurity devices and nontarget bait consumption during aerial baiting for the mouse eradication. The presence of relatively high weka densities (approximately two per hectare) on the island during the time of a mouse population establishing indicates that weka are a relatively poor bio-control agent for mice, contrary to recent discussions in the literature (Carpenter et al 2021).…”

Factors limiting kererū (Hemiphaga novaeseelandiae) populations across New Zealand

“…While some predation of kererū nests and adults by endemic predators would have occurred in prehuman times (e.g. by Eyles' harrier (Circus eylesi); Carpenter et al 2021), population viability modelling suggests that the rates of failure we have summarised here would lead to populations declining (Lyver et al 2009).…”

When origin, reproduction ability and diet define the role of birds in invasions

“…One exception in our database was the New Zealand weka ( Gallirallus australis ), a flightless rail that has been introduced on several islands of New Zealand were it predates on endemic threatened species, but which is also threatened in its native island by invasive alien mammals (e.g. rats) [62]. Moreover, IAS-threatened birds present similar ecological strategies as documented extinct species (e.g.…”