Predation by Mammalian Predators at Breeding Sites

Invasive alien species have had destructive effects on wildlife worldwide, particularly seabirds and other fauna on islands that had not evolved effective natural defences against mammalian ground predators. The most widespread alien species with the greatest impacts on seabirds tend to be predators, although invasive herbivores and plants can cause habitat deterioration and fragmentation, and introduced pathogens and insect vectors can becomes serious problems for animal health. Of the mammalian predators, the most common threats to seabirds at breeding sites in Australasia are feral cats, rats, house mice and stoats Mustela erminea.

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Given the major problems posed by alien species, there are multiple ongoing management regimes aimed at local control of predators at several breeding sites, including those of Westland Petrel Procellaria westlandica and Northern Royal Albatross (D. sandfordi) on the South Island of New Zealand, Purple Swamphen (Porphyrio porphyrio) on Phillip Island (Norfolk Island group), Red Fox Vulpes vulpes on Phillip Island (Victoria, Australia) and rats on Lord Howe Island.

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The number of high-profile campaigns to eradicate alien mammals from islands has increased over the last 25 years, and has included the successful campaign (10 years from planning to completion, at a cost of $AUD 24 million) to eradicate European Rabbits Oryctolagus cuniculus, black rats R. rattus and house mice from Macquarie Island. This campaign used a combination of rabbit calicivirus, aerial baiting and hunting by a team with trained detector dogs. It is important to recognise that these campaigns can result in substantial non-target mortality; at least 2500 birds died as a result of primary, secondary or tertiary ingestion of brodifacoum at Macquarie Island, including c.760 Northern Macronectes halli and Southern M. giganteus Giant Petrels, with substantial short-term impacts on their local populations. Non-target mortalities were reduced by a range of mitigation measures, and it is anticipated that both species’ populations will recover.

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Although there have been successful, high-profile eradications of invasive alien species from islands around Australasia in recent years (Lord Howe, Macquarie and Campbell Islands), further campaigns are planned or warranted. Feasibility plans have been produced for a number of other breeding sites: e.g., feral pigs Sus scrofa on the Auckland Islands (subantarctic New Zealand), and in some cases planning is well advanced and eradications are scheduled for the next few years. These need to be accompanied by better use of the underlying science in the peer-reviewed literature in order to improve methodologies, reduce risk of failure and minimise the poisoning of non-target species.