Responses of New Zealand forest birds to management of introduced mammals (original) (raw)

Recent advances in the control of mammalian predators have begun to reveal interspecific competition as a key driver in the structure of New Zealand forest bird communities once predation pressure is reduced. We present evidence that, when at high densities, South Island robins (Petroica australis) may be responsible for declines in a suite of smaller native and introduced songbird species. Bird surveys undertaken on 47 islands in Breaksea Sound and Dusky Sound, Fiordland, during 1974 to 1986, were repeated on the same islands in 2016 or 2019. During the first block of surveys, Norway rats (Rattus norvegicus) were present on two islands, and stoats (Mustela erminea) were known or presumed to regularly reach 43 of the remaining islands. The rats were eradicated in 1986 and 1988, and stoats have been controlled to zero density since 2001 on all 28 of the islands surveyed in Dusky Sound, and since 2008 on 12 of 19 islands surveyed in Breaksea Sound. Bird species that apparently benefit...

In New Zealand, invasive non-native mammals threaten the survival of native species such as the North Island brown kiwi (Apteryx mantelli). At Whangarei Heads, in northern New Zealand, community groups are working with local and national government agencies to protect kiwi populations. The abundance of kiwi there has been monitored since 2001 using annual counts of calls. Trapping of invasive mammals began in 2002, and their relative abundance is assessed from annual capture rates. Capture rates of stoats (Mustela erminea), weasels (M. nivalis), cats (Felis catus), rats (Rattus spp.) and possums (Trichosurus vulpecula) have declined significantly since trapping began, suggesting their abundance has been suppressed. Ferrets (Mustela furo) were already scarce when trapping began, and have been reduced to undetectable levels in most years. Numbers of hedgehogs (Erinaceus europaeus) have shown little response to trapping. Kiwi populations were apparently in decline before pest control began, but have since increased. Kiwi call rates in 2011 were the highest so far recorded at Whangarei Heads. Stoats are considered one of the main threats to kiwi, and our data suggest that kiwi numbers remain low unless stoat abundance is reduced below a catch per unit effort threshold of ~0.1 stoat per trap per year.

Abstract: The impacts of introduced mammalian predators on the viability of bird populations in forest, river and coastal habitats in New Zealand are well known. However, a common understanding of their impacts in freshwater wetlands is lacking. We review evidence for impacts of introduced mammalian predators on freshwater birds, particularly specialist species restricted to wetlands, and use this information to make predictions about freshwater species likely to be vulnerable to predation. Extinctions and significant declines of freshwater species have been numerous since humans introduced mammalian predators to New Zealand. Anecdotal evidence links predation to the loss of 11 of 14 extinct birds that would have inhabited wetlands. Thirty extant species, particularly ground-nesting species, are still under threat from mammalian predators. All introduced mammalian predator species are abundant and/or widespread in New Zealand wetlands and most have been confirmed to prey upon freshw...

Numbers of bellbird (Anthornis melanura), an endemic honeyeater, counted along transects in forest remnants on the Port Hills near the city of Christchurch, New Zealand, increased since the initiation of intensive mammalian pest control in 2006. Bellbird counts also increased along transects in bush reserves and along a 6.5 km cycle route in the city itself, probably as a result of spill-over from source populations on the Port Hills, because few bellbirds breed in the city. In contrast, counts of bellbirds in domestic gardens in the city did not increase, perhaps because of the continued presence of introduced mammalian predators and/or lack of suitable habitat. We suggest the increased abundance of bellbirds in forest remnants on the Port Hills was likely the result of mammalian pest control but the lack of 'no-treatment' areas means we cannot rule out other causes of the increase such as changing habitat and food availability. Spurr, E.B.; Crossland, A.C.; Sagar, P.M. 201...