stoats

Kākā (Nestor meridionalis) are vulnerable to predation by stoats (Mustela erminea) and possums (Trichosurus vulpecula), particularly when nesting. Without predator control kākā populations decline. Control of stoats and possums both by trapping and aerial application of the poison 1080 leads to increased kākā nesting success. In recent years, many 1080 poison operations have been undertaken to control ship rat (Rattus rattus) and stoat plagues that occur after beech mast. Kākā do not breed every year but breed in anticipation of heavy fruiting.

Stoats are implicated in the severe decline of certain iconic endemic species in New Zealand. Stoats are notoriously difficult to control, as they are highly cryptic and often neophobic around control techniques such as traps and poison baits in tunnels. Stoats are often killed through secondary poisoning in both aerial and hand-lay operations targeting other mammalian pests. We prototype trialled a novel approach to poisoning of stoats: wild-caught ship rats that had consumed (and subsequently died from) a lethal dose of 1080 cereal baits in a captive facility.

Conservation programmes aiming to suppress or remove invasive small mammal populations that threaten endemic fauna assume that eliminating an individual predator has the same effect as eliminating a conspecific in terms of decreasing risk to the prey species. However, marked between-individual variation in prey take could, at times, lead to uneven predation pressure. Such variation in the diets of introduced predators has long been hypothesised in New Zealand, suggesting that some observed rates of predation are not typical of the prey population as a whole.

The influence of micro-habitat on stoat (Mustela erminea) and rat (Rattus rattus) capture success was explored using trapping data collected from large scale predator control operations at the Okarito and Moehau Kiwi (Apteryx spp.) sanctuaries. Generalised linear models were used to explore the relationship between micro-habitat predictors and predator kill trapping records from individual trap sites. Our results suggest that micro-habitat information can provide useful predictors of rat and stoat capture success.

Most research into the diet of stoats in New Zealand has been in low altitude valleys such as the Eglinton and Hollyford Valleys. Yet much of New Zealand’s national parks (e.g. Fiordland National Park) consist of many small montane valleys and alpine areas. This research identified the key prey species of stoats inhabiting such small montane valleys and alpine grasslands.

A simple deterministic accounting model was used to predict the rate at which a colonising stoat (Mustela erminea L.) population would reach specified sizes. The model was used to explore how the size and composition of the founder population, and the survival schedule to which it was exposed, influenced this rate. A function used in disease surveillance was modified to predict the number of tracking tunnels necessary to detect the presence of the colonising Population with a specified degree of confidence.

A poison baiting operation at Trounson Kauri Park in Northland, New Zealand using first 1080 and then brodifacoum targeted possums (Trichosurus vulpecula) and rodents (Rattus rattus, Rattus norvegicus and Mus musculus). Predatory mammals were monitored by radio telemetry during the operation. All six feral cats (Felis catus), the single stoat (Mustela erminea) and the single ferret (Mustela furo) being monitored at the beginning of the operation died of secondary poisoning following the 1080 operation.

Stoats were monitored by three methods through an aerial 1080 poisoning operation at Waimanoa, Pureora Forest in August 1997. Tracking rates and number of live captures were used as indices of abundance, and radio-transmitters were used to follow individual animals. All 13 stoats with radio-transmitters within the poisoned area died between 2-18 days after the operation. No mustelids were tracked or live-trapped after the operation for three months. Of the radio-tracked stoats that died, rat remains occurred in 67%, passerine birds in 17%, cave weta in 17% and possum in 8%.

This radio-tracking study reports the daily activity rhythms in autumn and spring of 11 stoats (Mustela erminea) (9 male, 2 female), 20 ferrets (M.furo) (8 m, 12 f) and 11 feral house cats (Felis catus) (7 m, 4 f) resident on coastal grassland, Otago Peninsula, New Zealand. Activity rhythms differed markedly amongst individual stoats in autumn, but little amongst individual cats and ferrets in either season. Stoats were equally active day and night in autumn, but were more active at day than at night in spring.