Selection of alpine grasslands over beech forest by stoats (

Predation by introduced stoats is now considered a major threat to the population viability of several New Zealand endemic bird species. Historically stoat research and management has focused on beech forests and little is known about the ecology of stoats in the alpine grasslands occurring above the natural altitudinal limit of beech forest. Several stoat control operations in beech forest valley floors in southern New Zealand assume that adjacent montane areas act as a barrier to stoat immigration. Stoats were live-trapped and radio-tracked in alpine grasslands above the Borland Burn, Fiordland National Park, during the summer and autumn of 2003 and 2004. Seventeen stoats were radio-collared and home ranges were estimated for 11 of them. These home ranges were used in a compositional analysis which showed that these stoats spent significantly more time in alpine grassland than in adjacent beech forest. Range cores calculated for six of these stoats were located high up in alpine grassland and contained very little beech forest. This means that montane areas that contain alpine grasslands are unlikely to be barriers to stoat immigration; rather they may be a source of dispersing stoats that reinvade control areas. Also, endemic animal species that inhabit alpine grasslands could be at risk from stoat predation.     

Lack of movement of stoats (

Little is known about the movement of stoats in alpine grassland, where several species of native birds, reptiles and invertebrates are potentially at risk from predation. Radio-tracking, live trapping and tracking tunnel techniques were used to sample stoats in two adjacent habitats to determine whether the home range of stoats in beech forest valley floors extends into neighbouring alpine grasslands in the Ettrick Burn Valley, Fiordland. If this is the case then trapping stoats in the more easily accessible beech forest valley floors might serve to protect endangered species inhabiting the adjacent but more remote alpine grasslands. Between December 2000 and March 2001, 415 radio locations were collected on 15 stoats and none were observed to make any significant movements between the two habitats. Stoats were active in alpine grasslands, and trapping in the adjacent beech forest valley would not have caught those stoats during the time-frame of this study. Further research is needed to determine long term impacts of trapping in beech forest on stoats in alpine grasslands. During the timeframe of this research stoats were more abundant in beech forest than in alpine grasslands, and tracking tunnels showed this trend to be consistent at other sites.     

The effects of mice on stoats in southern beech forests

Introduced stoats (Mustela erminea) are important invasive predators in southern beech (Nothofagus sp.) forests in New Zealand. In these forests, one of their primary prey species – introduced house mice (Mus musculus), fluctuate dramatically between years, driven by the irregular heavy seed‐fall (masting) of the beech trees. We examined the effects of mice on stoats in this system by comparing the weights, age structure and population densities of stoats caught on two large islands in Fiordland, New Zealand – one that has mice (Resolution Island) and one that does not (Secretary Island). On Resolution Island, the stoat population showed a history of recruitment spikes and troughs linked to beech masting, whereas the Secretary Island population had more constant recruitment, indicating that rodents are probably the primary cause for the ‘boom and bust’ population cycle of stoats in beech forests. Resolutions Island stoats were 10% heavier on average than Secretary Island stoats, supporting the hypothesis that the availability of larger prey (mice verses wētā) leads to larger stoats. Beech masting years on this island were also correlated with a higher weight for stoats born in the year of the masting event. The detailed demographic information on the stoat populations of these two islands supports previously suggested interactions among mice, stoats and beech masting. These interactions may have important consequences for the endemic species that interact with fluctuating populations of mice and stoats.     

Stoat density, diet and survival compared between alpine grassland and beech forest habitats

In New Zealand, alpine grasslands occur above the treeline of beech forest. Historically stoat control paradigms in New Zealand?s montane natural areas have assumed alpine grassland is a marginal habitat that limits dispersal between beech forest stoat populations. We compared the summer-to-autumn (January?April) density, weight, diet and winter survival of stoats between these two habitatsduring years of low beech seedfall. Stoats were live-trapped, marked and released in alpine grassland and low-altitude beech forest in the Borland Valley, Fiordland National Park, during 2003 and 2004, and were caught and euthanased for necropsy in 2005. Stoat density was estimated using spatially explicit capture?recapture (SECR). The proportion of stoats marked in one year but recaptured in the next was used as a measure of ?observed survival?. Prey remains were identified from scats collected during 2003 and 2004 and stomachs from stoats killed in 2005. Stoat density was similar in both habitats over the two years, about one stoat per square kilometre. Observed survival from 2003?2004 was also similar, but survival from 2004?2005 was higher in alpine grassland than in beech forest. In 2003, male stoats were on average heavier in alpine grassland than in beech forest, although average weights were similar in the other years. Diet differed significantly between the two habitats, with stoats in alpine grasslands eating mainly ground weta (a large invertebrate) (72%) and hares (23%), while stoats in beech forest ate mainly birds (31%) and mice (19%). Collectively these results suggest that alpine grasslands are not a poor quality habitat for stoats. Traditionally it has been thought that stoats cannot survive on invertebrate prey alone. This research demonstrates that stoats relying largely on invertebrate prey can occur at similar densities and with equivalent survival to stoats relying on vertebrate prey.     

The biology of the stoat (Mustela erminea) in the National Parks of New Zealand VI. Infestation with Skrjabingylus nasicola

Abstract

The natural distribution of the parasite Skrjabingylus nasicola was surveyed in 1492 stoats from New Zealand’s National Parks. Infestation was rare in the young, so distribution was expressed as frequency of occurrence of skulls containing nematodes in samples of stoats more than 6 months old. Conservative estimates of incidence ranged from 0 to 37% in 27 local subsamples with at least 6 adults and subadults (mean 10%, n = 1005), sometimes varying substantially across short distances. Incidence was highest in beech forest and scrub/grassland habitats with annual rainfall less than 1600 mm. Subadult males (6–10 months old) were infested as frequently as adult males (older than 10 months), and there was no difference in incidence between the sexes. Worms recovered from 97 infested stoats occurred equally often in either side of the skull; were more often large (i.e., probably female) at all intensities of infestation; and numbered 1–73 per infested stoat (mean 12.9 in females, 14.2 in males; difference not significant). There was no evidence that infested stoats were smaller or lighter than uninfested onces.     

A population study of the metastrongylid nematode Skrjabingylus nasicola in the weasel Mustela nivalis

Analyses of adult worms of Skrjabingylus nasicola occurring in the nasal sinuses of the weasel Mustela nivalis from three localities in the British Isles show that the intensity of infestation can be correlated with increasing severity of skull damage, which in turn increases as the weasel ages. It is suggested that, apart from hormonal differences, the smaller sized female skull is likely to be linked with lower levels of infestation in female compared with male weasels. Also a reduction in mean worm length in female skulls and in heavy infestations of S. nasicola is probably the result of a "crowding effect", previously described for other helminth infections in the definitive host. Crowding appears to have no effect on the sex ratio of worm populations, although there is a tendency for the ratio of female: male worms to increase in female weasels. Reasons for this are discussed.     

An analysis of a recreational hunter's red deer tallies in the Tararua Ranges, North Island, New Zealand

Home range and diet of stoats inhabiting beech forest were examined by trapping and radio-tracking. Eleven stoats (6 female, 5 male) were fitted with radio-transmitters. Minimum home ranges of five females averaged 124 ± 21 ha and of four males 206 ± 73 ha. Range lengths of females averaged 2.3 ± 0.3 km and of males 4.0 ± 0.9 km. These differences were not statistically significant. Adult female stoats appeared to have mutually exclusive home ranges. Two females and one male had home ranges that were bisected by the Eglinton River. All three crossed the river regularly and could only have done so by swimming. Bird remains were found in 54% of stoat guts and scats examined, lagomorphs in 33%, and invertebrates in 34%. Australian brushtail possum remains were found in 11% of samples overall, but only in guts and scats from male stoats. A road through the study area affected the behaviour of stoats. Females avoided the road but males preferred it and were found scavenging road-kills, which may explain why they are more frequently found as road-kills themselves. In most years, New Zealand beech forest may be marginal habitat for stoats. No breeding was detected in the year of our study but there had been high productivity in the previous season. Stoats probably survive in this habitat because they are flexible in their diet and because their breeding biology allows them to respond rapidly to a sudden increase in food availability.     

Variation in body size, sexual dimorphism and age-specific survival in stoats, Mustela erminea (Mammalia: Garnivora), with fluctuating food supplies

Most hypotheses attempting to explain the evolution of pronounced sexual dimorphism in body size in the three species of weasels (Mustela erminea, M. frenata, M. nivalis) assume that sexual dimorphism is a long-term adaptation, associated with the different reproductive strategies of the two sexes. We here examine an auxiliary hypothesis which predicts that the degree of sexual dimorphism may also vary over the short-term, because when food is temporarily abundant, sexual selection should favour a greater growth rate of males than of females. This hypothesis concerns a phenotypic response which could introduce temporarily increased variation into an existing genotypic trait. We document the present size and sexual dimorphism of stoats introduced last century to New Zealand from Britain in relation to between-year variation in food supply in a single habitat (forests of southern beech, Nothofagus sp.). Southern beech trees produce heavy crops of flowers and seed at 3–5 year intervals, which are associated with very variable supplies of important prey of stoats, including several species of seed-eating birds, litter-feeding insects, and feral house mice (Mus musculus). Alternative prey are scarce. Regressions of condylobasal length and head-body length on mouse population indices were significant in both sexes. Mean condylobasal length was larger in both male and female stoats born after a heavy seedfall compared with those born in non-seedfall years. However, the largest males born in years of heavy seedfall were removed by selective mortality before the age of 3 years, so the condylobasal lengths for old (≥ 3.0 yr) males converged on a common mean regardless of food supply in their birth year. Sexual dimorphism did not vary with food supplies (as reflected in seedfall records or mouse population indices) at any age. First-year survivorship, at least from the age of independence, was significantly negatively correlated with density of stoats in the summer of their birth year.     

Beech forest management does not affect the infestation rate of the beech scale Cryptococcus fagisuga across three regions in Germany

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The biology of the stoat (Mustela erminea) in the National Parks of New Zealand III. Morphometric variation in relation to growth,geographical distribution,and colonisation

Abstract

A total of 1599 stoats were collected from 14 study areas (including all 10 National Parks) from 1972 to 1976. Samples were larger in summer, and contained more females. Young stoats are born in September-October, and females reach adult weight by the following March, though males not until after August. There was significant geographic variation in the body size of adult stoats sampled: males from lowland podocarp/broadleaved forests averaged 3% smaller than males from upland beech forests in skull length, and 4% smaller in head-and-body length. This pattern was repeated, less clearly, in females and in young (approximately 2–5 months old). In contrast with stoats in Britain, assumed to be still the same size as the colonising stock introduced into New Zealand in 1884 and subsequently, males from lowland podocarp forests were unchanged or possibly smaller, and males from upland beech forests were larger; females were larger in all habitats. In males, the extent of geographic variation is almost as great in New Zealand as in the whole of continental Europe. Possible explanations of this pattern are discussed.     

Non-invasive methods for genotyping of stoats (

Stoats (Mustela erminea) are a significant pest in New Zealand. A critical aspect of their management is the ability to identify individuals in order to estimate abundance or to determine the origin of residual animals after control, particularly as the trap-shy nature of stoats reduces the utility of trapping to gain this information. We investigated non-invasive ?capture? methods as an alternative to live-trapping or removal methods for estimating stoat abundance. First we determined whether sufficient variability exists at six microsatellite DNA loci to reliably identify individuals in the potentially bottlenecked, introduced stoat populations of New Zealand. In December 2001 we conducted a 7-night pilot field experiment using a modified hair-tube design, where we obtained a total of 64 hair samples. Sufficient DNA was extracted from 3?6 hair follicles to genotype a total of 51 samples. DNA quality declined if samples were left in the field for several nights before being collected, and daily checks proved best for maximising the quality of DNA obtained, while minimising the risk of multiple ?captures? of stoats. Conclusions were that non-invasive molecular sampling is likely to be a viable technique for estimating population density of stoats in New Zealand beech forest but that additional variable loci are required.     

Effect of host-tree and environmental variables on honeydew production by scale insects (

Honeydew excreted by phloem-sap sucking scale insects (Ultracoelostoma sp.) living in the bark of beech (Nothofagus solandri:) trees growing at a high elevation (900 m) site in the Craigieburn range of Canterbury, New Zealand, was measured over four days during 1–10 May 1996. Average standing crop of honeydew sugar was 3.1 mg m-2, and ranged from 0.4 to 5.5 mg m-2. Daily production of honeydew sugar ranged from 0.2 to 1.5 mg insect-1 24 h-1, and 4.1 to 45.9 mg m-2 24 h-1. Honeydew production varied significantly between trees, and trees with the highest mean individual rates of production (mg sugar insect-1 24 h-1) tended to be those with the highest numbers of insects per unit bark area. Air temperature averaged over the 24 hours preceding each production sample explained 65% of the variability in 3-hourly honeydew production, showing that honeydew production is controlled by environmental and host-tree variables. Using this data, together with previously published estimates of carbon uptake and seasonal variability in honeydew standing crop, it was estimated that carbon contained in honeydew is equivalent to 1.8% of net primary production of beech trees at Craigieburn. Determining the effects of environmental variables on tree and insect physiology will allow formulation of an environmentally-driven process-based model of honeydew production.     

Seasonal variation in the honeydew, invertebrate, fruit and nectar resource for bellbirds in a New Zealand mountain beech forest

To examine the seasonal availability of the major bellbird (Anthornis melanura) food sources in a mountain beech (Nothofagus solandrivar. cliffortioides) forest at Craigieburn, the invertebrate, honeydew, and mistletoe (Peraxilla tetrapetala and Alepis flavida) fruit and nectar resources were sampled over 12 months. The total available food varied 2.6-fold from a low in October (8798 kJ/ha) to a high in December (22,959 kJ/ha) with an annual mean of 15,782 kJ/ha. Invertebrates were available all year and represented 89% of the available food energy. Only 16% of the invertebrate resource was on beech foliage, and beech trunks with honeydew had 60% more invertebrate energy than trunks without honeydew. The energy value of honeydew at Craigieburn (0.9% of the total) was much lower than at lower altitude sites. The relative rankings of honeydew standing crops on 25 permanently marked trees were very constant. On an annual basis mistletoe nectar and fruit made up 6.3% and 4.9%, respectively, of total food energy, but P. tetrapetala nectar was 46% of available food in early January, and P. tetrapetala fruit was 25% of the total in March. Bellbirds spent less time foraging on invertebrates, and more time on the other foods, than energy values would predict. However, during the Peak of its short flowering season, P. tetrapetala nectar made up 46% of available energy but only 33% of bellbird foraging observations. At this site P. tetrapetala is pollen limited due to insufficient visits from pollinators. This may be because bellbirds require invertebrates for protein, or to feed to nestlings. Therefore the pollination mutualism is faltering, despite high investment in nectar by the plant.     

The effects of the nematode parasite Skrjabingylus nasicola on British weasels (Mustela nivalis)

Adult worms of Skrjabingylus nasicola are found in the nasal sinuses of mustelids, and when numerous may cause considerable distortion of the frontal bones. A heavy infestation is commonly assumed to be detrimental to the individual and possibly also to the population. To examine this belief, the frequency of occurrence ("incidence") and extent of damage caused by S. nasicola were analysed with respect to the climate of seven sample areas and the age, sex and body size of 614 British weasels. Incidence ranged from 69–100% of the sample, and mean skull damage from 31 to 53 on an index scale of 0–8 points. Significant correlations were found between incidence and date of collection of young weasels, and between extent of damage and mean number of rain-days in the area. Male weasels were more badly damaged than females, though incidence was the same in both sexes. There was no evidence that badly damaged weasels were smaller, lighter, leaner or died sooner than lightly or undamaged ones, nor that, in the wild, they were infested by eating shrews.     

Review of South-Island High Country Land Management Issues-Joint Submission to the Ministerial High Country Review Committee from the New Zealand Ecological Society and the New Zealand Society of Soil Science

Recent work at several central South Island sites has shown that the bird-pollinated mistletoe Peraxilla tetrapetala (Loranthaceae) is extensively pollen-limited. We studied the diet, time-budget, and densities of its principal pollinator, bellbirds (Anthornis melanura, Meliphagidae), at Craigieburn to find out what aspect of bellbird ecology may be limiting pollination. Direct observations of bellbird diets showed that they are annual generalists on invertebrates (diet range 22-85% of food items) and honeydew (diet range 2-45%), and concentrate seasonally on mistletoe fruit (18-60%) and mistletoe nectar (27-58%) when available. The bellbirds at Craigieburn are more insectivorous than New Zealand's other two honeyeaters (tui and stitchbirds). In general, bellbirds are most similar to the short-billed guild of Australian honeyeaters in their beak morphology, foraging behaviour, and diet choice, but with a greater importance of fruit in the bellbird diet. The annual mean number of bellbirds recorded per 5-minute count (1.05) at Craigieburn was relatively low, even compared to other eastern South Island sites, which have lower counts of bellbirds than the western South Island and offshore islands. As mistletoe fruit and nectar were preferred foods when in season, and bellbird counts were low at Craigieburn, we conclude that it is the probable low number of bellbirds in the area, and not their choice of diet, which limits mistletoe pollination and dispersal. The bellbird population at Craigieburn did not appear to be food limited as bellbirds spent less than 20% of their time feeding, and the number of hours per day bellbirds spent feeding and foraging did not change significantly from winter to summer while food resources became more plentiful. Other pressures that limit the bellbird population size, particularly predation from introduced mammals, would appear more likely explanations for poor pollination and disperser services to mistletoes at Craigieburn.     

Understanding contributions of cohort effects to growth rates of fluctuating populations

1. Understanding contributions of cohort effects to variation in population growth of fluctuating populations is of great interest in evolutionary biology and may be critical in contributing towards wildlife and conservation management. Cohort-specific contributions to population growth can be evaluated using age-specific matrix models and associated elasticity analyses. 2. We developed age-specific matrix models for naturally fluctuating populations of stoats Mustela erminea in New Zealand beech forests. Dynamics and productivity of stoat populations in this environment are related to the 3-5 year masting cycle of beech trees and consequent effects on the abundance of rodents. 3. The finite rate of increase (lambda) of stoat populations in New Zealand beech forests varied substantially, from 1.98 during seedfall years to 0.58 during post-seedfall years. Predicted mean growth rates for stoat populations in continuous 3-, 4- or 5-year cycles are 0.85, 1.00 and 1.13. The variation in population growth was a consequence of high reproductive success of females during seedfall years combined with low survival and fertility of females of the post-seedfall cohort. 4. Variation in population growth was consistently more sensitive to changes in survival rates both when each matrix was evaluated in isolation and when matrices were linked into cycles. Relative contributions to variation in population growth from survival and fertility, especially in 0-1-year-old stoats, also depend on the year of the cycle and the number of transitional years before a new cycle is initiated. 5. Consequently, management strategies aimed at reducing stoat populations that may be best during one phase of the beech seedfall cycle may not be the most efficient during other phases of the cycle. We suggest that management strategies based on elasticities of vital rates need to consider how population growth rates vary so as to meet appropriate economic and conservation targets.     

Using genetic techniques to quantify reinvasion,survival and in situ breeding rates during control operations

Determining the origin of individuals caught during a control/eradication programme enables conservation managers to assess the reinvasion rates of their target species and evaluate the level of success of their control methods. We examine how genetic techniques can focus management by distinguishing between hypotheses of ‘reinvasion’ and ‘survivor’, and defining kin groups for invasive stoats (Mustela erminea) on Secretary Island, New Zealand. 205 stoats caught on the island were genotyped at 16 microsatellite loci, along with 40 stoats from the opposing mainland coast, and the age and sex were determined for each individual. Using these data, we compare and combine a variety of genetic techniques including genetic clustering, population assignment and kinship‐based techniques to assess the origin of each stoat. The population history and individual movement could be described in fine detail, with results indicating that both in‐situ survival and breeding, and reinvasion are occurring. Immigration to the island was found to be generally low, apart from in 1 year where around 8 stoats emigrated from the mainland. This increased immigration was probably linked to a stoat population spike on the mainland in that year, caused by a masting event of southern beech forest (Nothofagus sp.) and the subsequent rodent irruption. Our study provides an example of some of the ways genetic analyses can feed directly into informing management practices for invasive species.     

Large‐scale pest control in New Zealand beech forests

In 2014, baits laced with the poison sodium fluoroacetate (1080) were sown over 694 000 ha of mostly native beech forests in New Zealand to control rats, stoats and possums – a landscape‐scale pest control programme called ‘Battle for our Birds’. This large pest control operation was necessitated by the mast seeding of beech trees which led to irruptions of rodent and stoats which were predicted to lead to decreases in vulnerable native wildlife. In this article, we describe why and how this extensive pest control programme was developed and implemented. We describe the seedfall monitoring that was used to determine the need for large‐scale rodent and stoat control and the response of these predators to this control. We also provide a summary of the bird monitoring that was undertaken to demonstrate the effectiveness or otherwise of the programme.     

Decline in capture rate of stoats at high mouse densities in New Zealand

We present two statistical models documenting variations in density indices of stoats and of mice in New Zealand southern beech (Nothofagus spp.) forests. They confirm previous, simpler correlations showing that the summer capture rate of stoats increases with spring mouse density index up to about 20–25 mouse captures per 100 trap-nights (C/100TN). However, at much higher mouse densities (60–80 C/100TN), observed in the Grebe and Borland Valleys in southern Fiordland in 1979/80 and again in 1999/2000, fewer stoats were caught than expected. These models quantify a serious decline in capture rate of stoats during periods of high mouse abundance over the range 25-80 C/100TN. At such times, management strategies aiming to protect threatened birds by intensive lethal trapping of stoats during the nesting seasons may be least effective just when they are most needed.     

Trappability and densities of stoats (

Stoat (Mustela erminea) density was estimated by live-trapping in a South Island Nothofagus forest, New Zealand, at 8-9 (Jan/Feb 1996) and 15-16 (Aug/Sep 1996) month intervals after significant beech seedfall in autumn 1995. Absolute densities were 4.2 stoats per km² (2.9-7.7 stoats per km², 95% confidence intervals) in Jan;Feb 1996 and 2.5 stoats per km² (2.1-3.5 stoats per km²) in Aug/Sep 1996. Trappability of stoats increased in the latter sampling period, probably because mice (Mus musculus) had become extremely scarce. accordingly, trapping rates of stoats may vary temporally and spatially with food supply rather than only with absolute abundance. Ship rats (Rattus rattus) capture rates doubled between Jan/Feb 1996 and Aug/Sep 1996, but rapidly declined shortly afterwards. Trappability of ship rats also increased in the latter sampling period. These factors must be considered when planning methods of indexing relative densities of stoats and rats.