Individual specialists within a generalist niche: variable diet of stoats and implications for conservation

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.

Stable isotope analysis reveals variable diets of stoats (Mustela erminea) in the alpine zone of New Zealand

The alpine zone of New Zealand covers c. 30% of public conservation land and is home to a high diversity of endemic species. Predation by introduced stoats (Mustela erminea) is identified as a major threat to alpine fauna. However, a lack of biological information, such as what stoats eat in different settings, hinders efforts to focus control measures in time and space in order to achieve the greatest conservation gains. We used a biochemical tool, stable isotope analysis, to estimate stoat diet across three time-periods in the alpine zone of three national parks.

Variability of little blue penguin (Eudyptula minor) diving behaviour across New Zealand

Foraging strategies of penguin species can vary according to the quality of the marine environment, and this influences their abundance and breeding success. Little blue penguins (Eudyptula minor) are considered a candidate species for assessing near-shore marine productivity due to their usually limited foraging ranges and reliance on local resources, particularly while rearing chicks.

New Zealand falcon prey selection may not be driven by preference based on prey nutritional content

Little is known about how diurnal raptors, as apex predators, select their prey. It has been hypothesised that they are opportunistic, taking prey according to availability, and that they select prey based on prey size. The threatened New Zealand falcon or kārearea (Falco novaeseelandiae) is New Zealand’s only remaining endemic bird of prey. A previous study on prey caught by kārearea during the breeding season suggested that introduced avian prey were taken more often than expected, and endemic avian prey taken less often than expected, based on their abundance.

Bone stable isotopes indicate a high trophic position for New Zealand’s extinct South Island adzebill (Aptornis defossor) (Gruiformes: Aptornithidae)

The adzebills (Aptornithidae) were an ancient endemic lineage of large flightless Gruiformes that became extinct shortly after Polynesian settlement of New Zealand. The diet and ecology of these enigmatic birds has long been a matter for conjecture, but recent stable isotope analyses of bones of the North Island adzebill (Aptornis otidiformis) have indicated that adzebills may have been predatory. Here, we add to our understanding of adzebill ecology by providing the first stable isotope analyses of South Island adzebill (A. defossor) bones from two Holocene deposits.

Feral pig (Sus scrofa) predation of a green and golden bell frog (Litoria aurea)

Feral pigs (Sus scrofa) are a threat to New Zealand’s biodiversity. Predation of frog species by feral pigs is a notable problem in other countries where pigs have been introduced. Our study aimed to determine through analysis of stomach contents if feral pigs are consuming frogs in the Waitakere Ranges, Auckland. Auckland Council contract pig hunters collected 274 feral pig stomach samples. Of these samples, 184 were screened for frog consumption via both dissecting microscope and DNA analyses.

Intraspecific variation in the foraging ecology of kea, the world’s only mountain- and rainforest-dwelling parrot

Intraspecific variation can have important knock-on effects on population dynamics and ecosystem processes. There are good indicators that intraspecific differences may exist in the foraging ecology of kea parrots (Nestor notabilis). Kea breed in two markedly different habitats (alpine and temperate rainforest), and have pronounced sexual size dimorphism of their upper bill, which may indicate niche partitioning between the sexes.

Causes and consequences of ground disturbance by feral pigs (Sus scrofa) in a lowland New Zealand conifer–angiosperm forest

The ecological impacts of feral pigs (Sus scrofa) are of concern in many places around the world. One noticeable impact is soil disturbance, although the causes and consequences are often unclear. We measured the effect of ground disturbance by feral pigs on seedling recruitment and soil ecology over 25 months on a forested riparian terrace at Waitutu, south Fiordland, New Zealand, and assessed the diet of pigs from the area from stomach contents of animals shot by hunters. Foraging by feral pigs for below-ground food disturbed between 7.4% and 12.4% of the soil.

A note on the food of feral pigs Sus scrofa) of Auckland Islands.

While studying the population of feral goats (Capra hircus L.) on the northern tip of main Auckland Island in summer 1972-73 (Rudge and Campbell, 1975) skeletons were looked for from which to estimate natural mortality. We found only two skulls, both without horns or lower jaws, and concluded that goat bodies were eaten by feral pigs. Some pig faeces were therefore collected around Port Ross, preserved in 10% formalin, and later washed apart on a I mm sieve. Identifiable items were listed as present or absent and scored by percent frequency of occurrence.

Habitat use and movements of the opossum (Trichosurus vulpecula) in a pastoral habitat on Banks Peninsula

The habitat use and movements of a population of Australian, brush-tailed opossums, Trichosurus vulpecula (Kerr), were studied by live-trapping, spotlighting and radiotelemetry in a mixed pasture, bush and scrub habitat on Banks Peninsula, New Zealand. Resident opossums had distinct ranges that for some animals varied in position and size and, for all, varied in intensity of use of habitat types during the year. Seasonal foods and breeding behaviour were reasons for shifts in ranges and changes in their sizes.