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Estimating the abundance and density of mountain ungulates is difficult because of rugged and remote terrain, high elevations, and rapidly changing weather. Helicopter surveys could overcome these problems, but researchers have seldom applied helicopter‐based survey methods at large spatial scales in mountain terrain. We used helicopters to count introduced Himalayan tahr (Hemitragus jemlahicus) at 117 plots, each of 4 km2, in New Zealand's Southern Alps during 2016–2019. The sampling frame was 7,844 km2 and we located the plots at the vertices of an 8‐km grid superimposed over the sampling frame (i.e., a systematic random sampling design). We conducted 3 repeat counts at each plot during summer–autumn. We used the repeat counts to estimate tahr abundance and density, corrected for imperfect detection, using a dynamic N‐mixture model for open populations. We estimated the population of tahr in the sampling frame using design‐based, finite sampling methods and model‐based inference procedures. The mean estimated density of tahr on each plot varied from zero to 31.7 tahr/km2. The mean densities of tahr varied among management units, ranging from 0.3 to 10.7 tahr/km2, and exceeded specified intervention densities in 6 of the 7 management units. The total design‐based estimate of tahr abundance in the sampling frame was 34,500 (95% CI = 27,750–42,900), with a coefficient of variation (CV) of 0.11. The corresponding model‐based estimate of total abundance was similar (34,550, 95% CI = 30,250–38,700) but was substantially more precise (CV = 0.06) than the design‐based estimate. The precision of the estimates for the individual management units was also better than that of the design‐based estimates, with CVs of <0.20 for all but 1 management unit. Our study provides a repeatable method for sampling mountain ungulates. More generally, robust estimation of abundance and density of mountain ungulates is possible by combining aerial surveys and open population models with an objective, probabilistic sampling design. [ABSTRACT FROM AUTHOR]

Introduced ungulates are an important management issue on New Zealand's public conservation land (PCL). Ungulates are harvested by recreational and commercial hunters, with some government-funded culling. A robust monitoring system is needed to reliably report trends in occupancy and abundance, and to evaluate management effectiveness. We first describe the design and implementation of a monitoring programme enabling ungulate occupancy and relative abundances to be estimated on New Zealand's PCL. Monitoring sites are located at the vertices of an 8-km grid superimposed over PCL on North, South and Stewart/Rakiura islands (i.e. a spatially representative sampling network). At each site, intact ungulate pellets are counted on four transects radiating from a 400 m2 vegetation plot, with each 150 m transect containing 30 1-m radius plots. We next report an analysis of the first such data collected at 1346 sites during 2012-2018. Nationally, ungulate occupancy and abundance were higher at woody than at non-woody sites, and overall were higher in the North Island than in the South Island. Occupancy odds increased by 34% and 21% per annum in the North Island and South Island, respectively. Abundance (conditional on sites being occupied) increased 11% annually in the North Island, but did not change in the South Island. These increases in occupancy and abundance indicate that ungulate populations are recovering from the lows of the 1980s, likely due to reduction in both commercial harvesting and government-funded control. The data from the monitoring reported here establish a baseline against which future estimates of ungulate occupancy-abundance, and the effectiveness of management activities, can be assessed. Five-yearly remeasurements at the sites, coupled with more comprehensive recording of information on government control and commercial/recreational harvesting activities, should enable the drivers of future changes in ungulate occupancy and abundance to be better understood. [ABSTRACT FROM AUTHOR]

There is interest in large-scale and unbiased monitoring of biodiversity status and trend, but there are few published examples of such monitoring being implemented. The New Zealand Department of Conservation is implementing a monitoring program that involves sampling selected biota at the vertices of an 8-km grid superimposed over the 8.6 million hectares of public conservation land that it manages. The introduced brushtail possum (Trichosurus Vulpecula) is a major threat to some biota and is one taxon that they wish to monitor and report on. A pilot study revealed that the traditional method of monitoring possums using leg-hold traps set for two nights, termed the Trap Catch Index, was a constraint on the cost and logistical feasibility of the monitoring program. A phased implementation of the monitoring program was therefore conducted to collect data for evaluating the trade-off between possum occupancy–abundance estimates and the costs of sampling for one night rather than two nights. Reducing trapping effort from two nights to one night along four trap-lines reduced the estimated costs of monitoring by 5.8% due to savings in labour, food and allowances; it had a negligible effect on estimated national possum occupancy but resulted in slightly higher and less precise estimates of relative possum abundance. Monitoring possums for one night rather than two nights would provide an annual saving of NZ$72,400, with 271 fewer field days required for sampling. Possums occupied 60% (95% credible interval; 53–68) of sampling locations on New Zealand’s public conservation land, with a mean relative abundance (Trap Catch Index) of 2.7% (2.0–3.5). Possum occupancy and abundance were higher in forest than in non-forest habitats. Our case study illustrates the need to evaluate relationships between sampling design, cost, and occupancy–abundance estimates when designing and implementing large-scale occupancy–abundance monitoring programs. [ABSTRACT FROM AUTHOR]

Assemblages of introduced taxa provide an opportunity to understand how abiotic and biotic factors shape habitat use by coexisting species. We tested hypotheses about habitat selection by two deer species recently introduced to New Zealand’s temperate rainforests. We hypothesised that, due to different thermoregulatory abilities, rusa deer (Cervus timorensis; a tropical species) would prefer warmer locations in winter than red deer (Cervus elaphus scoticus; a temperate species). Since adult male rusa deer are aggressive in winter (the rut), we also hypothesised that rusa deer and red deer would not use the same winter locations. Finally, we hypothesised that in summer both species would prefer locations with fertile soils that supported more plant species preferred as food. We used a 250 × 250 m grid of 25 remote cameras to collect images in a 100-ha montane study area over two winters and summers. Plant composition, solar radiation, and soil fertility were also determined for each camera location. Multiseason occupancy models revealed that direct solar radiation was the best predictor of occupancy and detection probabilities for rusa deer in winter. Multistate, multiseason occupancy models provided strong evidence that the detection probability of adult male rusa deer was greater in winter and when other rusa deer were present at a location. Red deer mostly vacated the study area in winter. For the one season that had sufficient camera images of both species (summer 2011) to allow two-species occupancy models to be fitted, the detection probability of rusa deer also increased with solar radiation. Detection probability also varied with plant composition for both deer species. We conclude that habitat use by coexisting tropical and temperate deer species in New Zealand likely depends on the interplay between the thermoregulatory and behavioural traits of the deer and the abiotic and biotic features of the habitat. [ABSTRACT FROM AUTHOR]

Although fecal pellet counts have been widely used to index changes in deer abundance in forests, few studies have modeled the relationship between the indices and deer density. We examined the relationships between 3 fecal pellet indices (total pellets, pellet groups, and pellet frequency) and the density of deer (primarily red deer [Cervus elaphus scoticus]) in 20 enclosures in the North and South islands of New Zealand. In each enclosure we estimated the 3 indices on 30 randomly located 150-m transects, with each transect having 30 circular plots of 3.14 m². We developed 4 candidate models (1 linear and 3 nonlinear) to describe the relationship between the indices and deer density. We used a Bayesian analysis to account for uncertainty in the estimates of deer abundance and to facilitate fitting models that included random transect effects. The 4 models explained the relationship between the 3 indices and deer density similarly well. The slopes of the linear relationships between the 3 indices and deer density were positive. Our results suggest that fecal pellet counts may be useful indices of deer abundance. [ABSTRACT FROM AUTHOR]

Introduced brushtail possums (Trichosurus vulpecula) are a widespread pest of conservation and agriculture in New Zealand, and considerable effort has been expended controlling populations to low densities. A national protocol for monitoring the abundance of possums, termed trap catch index (TCI), was adopted in 1996. The TCI requires that lines of leghold traps set at 20-m spacing are randomly located in a management area. The traps are set for 3 fine nights and checked daily, and possums are killed and traps reset. The TCI is the mean percentage of trap nights that possums were caught, corrected for sprung traps and nontarget captures, with trap line as the sampling unit. We studied 1 forest and 1 farmland area in the North Island, New Zealand, to address concerns that TCI estimates may not be readily comparable because of seasonal changes in the capture probability of possums. We located blocks of 6 trap lines at each area and randomly trapped 1 line in each block in 3 seasons (summer, winter, and spring) in 2000 and 2001. We developed a model to allow for variation in local population size and nightly capture probability, and fitted the model using the Bayesian analysis software BUGS. Capture probability declined with increasing abundance of possums, generating a nonlinear TCI. Capture probability in farmland was lower during spring relative to winter and summer, and to forest during summer. in the absence of a proven and cost-effective alternative, our results support the continued use of the TCI for monitoring the abundance of possums in New Zealand. Seasonal biases in the TCI should be minimized by conducting repeat sampling in the same season. [ABSTRACT FROM AUTHOR]

Presents a study which compared the factors that affect the introduction success of ungulates and bird species introduced to New Zealand. Methods; Results of the study.

1. Sexual differences in behaviour and ecology have important implications for the management of harvested ungulate populations. 2. This study investigated the long-term effects of harvesting on the abundance and distribution of sexes within an introduced population of Himalayan tahr in the Two Thumb and Sibbald Ranges, New Zealand. Annual counts of tahr were made from 1984 to 1996 in two catchments subject to different harvest regimes. 3. Although populations in the two catchments increased at similar rates over the study period, their adult sex ratios diverged significantly in the late 1980s. In Carneys Creek, which was subject to unrestricted harvest, the adult sex ratio was initially equivalent to the estimated population sex ratio, but from 1991 it was significantly male-biased. In North Branch, 10 km from Carneys Creek but subject only to adult (trophy) male harvest, the population was significantly female-biased in all years. 4. There was a large and male-biased harvest in Carneys Creek in 1993, suggesting that immigration of males may have been responsible for the long-term changes in sex ratio observed there. In contrast, the harvest of males in North Branch was insufficient to explain its female-biased population. 5. Monthly counts of male and female tahr in Carneys Creek between December 1993 and February 1996 revealed a consistent seasonal change in the abundance of sub-adult males, and perhaps adult males, but not females. Sub-adult males immigrated into Carneys Creek during spring, increasing to a summer maximum before emigrating during autumn; few sub-adult males were present during winter. 6. Counts at six additional sites during summer and autumn 1996 indicated that the probable source of these males was an adjacent hunting reserve. This hunting reserve, which included North Branch, contained a female-biased population with moderate female density. 7. The observed changes appear to have been a consequence of sexual differences in habitat... [ABSTRACT FROM AUTHOR]

In 2003, a review of how introduced mammals were managed as pests in New Zealand was published. Since then trends for the control of these mammals include moves from pest-by-pest prioritisation towards site-based and multiple-pest management, extension of large-scale aerial control of predators to include beech forests, increasing intensive management of sites by private and non-government agencies, and increasing effort by regional councils and managers of vectors of bovine tuberculosis. The current deployment is the sum of largely independent decisions made by different agencies and individuals with different priorities. National agencies might optimise their own decisions, but overall deployment will always be nationally suboptimal when objectives are set at regional or local scales. This system includes both small areas where most of the mammals present are managed intensively and large areas where fewer species are managed. We discuss how this deployment might evolve as a network of smaller core areas aiming to achieve zero or low densities of all or most pests, with surrounding halos with lesser control effort against fewer species, enough to allow for at least 'safe passage' of native animals between the cores. This system might work best along the more-or-less contiguous native habitats along the axial ranges of the North and South Islands, especially if agencies with a national mandate are prepared to act in the extensive areas between core sites. Some have asked whether the successful eradication of mammals on small islands can be scaled up to the main islands of New Zealand. The current version of this predator-free model aims at the ubiquitous ship rat, brushtail possum and stoat. A key need for the predator-free model is a tool that kills 100% of each of the three main target species, ideally with one large-scale, socially-acceptable application. Without this tool the cost to find and kill survivors would raise the costs of national eradication to about $32 billion, assuming current costs of multiple-species eradications on islands. For sustained control options, research is needed to inform the frequency and intensity of control, and thus the best control tools. The ability to detect target pests at low densities and management of reinvasion are essential for achieving zero or low pest density goals. We suggest that the core/halo model of pest management, within a network of assets to be protected, will best protect New Zealand's biodiversity for the foreseeable future. The national scale pest- or predator-free aspiration is not currently (and may never be) feasible and risks diverting resources from more optimal solutions, as occurred with the 'last rabbit' and 'last deer' programmes promoted last century. [ABSTRACT FROM AUTHOR]

Government conservation agencies in New Zealand and the Australian state of Victoria spend 20% and 4%, respectively, of their annual budgets to manage a small part of the problem caused by introduced mammals. Managers' uncertainty about the optimal strategies for applying pest control has led to major differences in management practices within the single pest control programs in both countries. Monitoring under a trial-and-error approach has not removed uncertainty but has led managers to support the application of adaptive management for their pest control Control of brushtail possums (Trichosurus vulpecula) in New Zealand and red foxes (Vulpes vulpes) in Victoria, Australia, is conducted over large areas in many operations, but individual managers apply different control regimes based on the perceived benefits and opportunity costs. We report on the processes used to set up the first adaptive management experiments in pest control in New Zealand or Australia that combine the competing models approach (used when only a single management regime can be applied at one time) with an experimental approach (made possible when different management regimes are applied simultaneously in different places) with the aim of elucidating benefits and costs of the different strategies used to control the 2 pests. [ABSTRACT FROM AUTHOR]

There is currently great interest in restoring ecosystems affected by invasive organisms. In New Zealand, deer were introduced during the nineteenth century, causing dramatic changes to the understory composition and structure of some forests. Deer prefer to browse on short tree species, mostly associated with early successional stands and moist-fertile sites, but many tall tree species are browsed only when other food sources are scarce. The government has invested heavily in control programs aimed at reducing deer numbers and thereby restoring forests to something approaching their preinvasion composition and structure, but have met with only limited success. Based on a literature review, we give several examples of situations in which deer impacts may not be reversible, including the following: (1) palatable species remaining highly browsed even at low deer densities as a result of diet switching; (2) occupation of vacated niches by plant species not eaten by deer; (3) local extinction of seed sources; (4) fundamental alterations to successional pathways; (5) shifts in ecosystem processes; (6) other exotic animals becoming naturalized and weakening the effectiveness of single-species control; and (7) exotic plants weakening the effectiveness of single-species control. We consider the contributions that scientific research can make to effective forest restoration, including empirically based forest-dynamics models that place regeneration in the context of other processes, such as disturbance, soil fertility, and multiple invasive organisms. [ABSTRACT FROM AUTHOR]

Wild mammalian herbivores can compete with domestic livestock and damage other types of production systems. We reviewed damage by wild mammalian herbivores, excluding rodents, to primary production in New Zealand and assessed whether primary producers alter stocking rates in response to changes in forage availability following pest control. Given the dearth of information on the damage caused by wild mammalian herbivores to many production systems, we primarily focused on their damage to agriculture. With the exception of the substantial damage that brushtail possums (Trichosurus vulpecula) and European rabbits (Oryctolagus cuniculus) cause, there are no quantitative estimates of pasture depletion by other wild mammalian herbivores on New Zealand farmland. Estimates of dry matter consumption by wild mammalian herbivores, converted to stock unit equivalents, suggest that several species can substantially reduce stocking rates when they occur on farmland. Quantitative data on the damage they cause to horticulture and silviculture are lacking, but damage to coniferous seedlings has been recorded for possums, wallabies (Notamacropus spp.), and some species of deer (Cervus spp., Rusa spp., and Dama dama). The process that primary producers use to decide whether to control wild mammalian herbivores includes complex social and economic factors, but quantitative information is important for weighing up the expected costs and benefits of pest control. However, it is unclear how primary producers manage livestock in response to increases in forage availability following pest control. The paucity of quantitative data on wild mammalian herbivore damage to production assets is a substantial knowledge gap. Key research priorities are (i) understanding how damage varies with pest density (critical information for effective pest management) and (ii) and how primary producers alter stocking rates following reductions in pest density. [ABSTRACT FROM AUTHOR]

Flightless birds were once the largest and heaviest terrestrial fauna on many archipelagos around the world. Robust approaches for estimating their population parameters are essential for understanding prehistoric insular ecosystems and extinction processes. Body mass and population density are negatively related for extant flightless bird species, providing a method for quantifying densities and population sizes of extinct flightless species. Here we assemble an updated global data set of body mass and population densities for extant flightless birds and estimate the relationship between these variables. We use generalised least squares models that account for phylogenetic relatedness and incorporate the effects of limiting factors (e.g. habitat suitability) on population density. We demonstrate the applicability of this allometric relationship to extinct species by estimating densities for each of the nine species of moa (Dinornithiformes) and generating a combined spatially explicit map of total moa density across New Zealand. To compare our density estimates with those previously published, we summed individual species' abundances to generate a mean national density of 2.02–9.66 birds km−2 for low‐ and high‐density scenarios, respectively. Our results reconcile the extreme bimodality of previous estimates (< 2 birds km−2 and > 10 birds km−2) and are comparable to contemporary densities of large herbivorous wild mammals introduced into New Zealand about 150 yr ago. The revised moa density has little effect on the harvest rates required to bring about extinction within 150–200 yr, indicating that rapid extinction was an inevitable response to human hunting, irrespective of the initial population of moa. [ABSTRACT FROM AUTHOR]

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. Pigs were seven times more likely to redisturb a site than to disturb a new site. Below-ground food items constituted a third of pigs' diet and were dominated by stag beetle larvae. Sites disturbed by feral pigs had shorter seedlings compared with undisturbed sites, but this was due to pigs' choice of sites rather than a consequence of the disturbance. Net temporal changes in density and height of seedlings were similarly slow in both disturbed and undisturbed sites. The basal respiration of microbes in soils recently disturbed by pigs was significantly higher than that for undisturbed soils. There was a suggestion that disturbed soils had higher ratios of fungi to bacteria than undisturbed soils (P = 0.06). This may reflect either disturbance favouring fungi over bacteria or selection of sites with more fungi or more of their main prey, the fungivorous stag beetle Dorcus helmsii. Our results indicate that pigs disturb soil primarily to forage for food and that the consequences of disturbance for seedling regeneration and soil ecology are limited or neutral. The consequences of ground disturbance and predation for populations of animal prey, such as the stag beetles, require further investigation. [ABSTRACT FROM AUTHOR]

1 Angiosperm trees often dominate forests growing in resource-rich habitats, whereas conifers are generally restricted to less productive habitats. It has been suggested that conifers may be displaced by angiosperms except where competition is less intense, because conifer seedlings are inherently slow growing, and are outpaced by faster-growing angiosperm species. Here we investigate whether competition with ferns and deeply shading trees also contributes to a failure of conifers to regenerate in resource-rich habitats. 2 We examined how changes in soil nutrient availability and drainage affected vegetation along the retrogressive stages of a soil chronosequence in southern New Zealand. Vegetation composition shifted from angiosperm-tree dominance on ‘recent’ alluvial terraces (< 24 ky), via coniferous-tree dominance on older marine terraces (79–121 ky), to coniferous-shrub dominance on the oldest marine terraces (291 ky). Soil drainage deteriorated along the sequence, and N : Pleaves and N : Psoil indicate increasing P-limitation. Conifer species appear to be adapted to persistence on infertile and poorly drained soils. 3 The floor of the relatively fertile alluvial forests was deeply shaded (∼1% light transmission) by dense groves of tree-ferns and ground-ferns, and by large-leaved subcanopy trees. Few seedlings of any type were found on the forest floor, even in tree-fall gaps, and establishment was restricted to rotting logs and tree-fern trunks. Angiosperms were particularly successful at colonizing these raised surfaces. 4 Less shade was cast by the conifer-dominated forests on infertile marine terraces (∼5% light transmission), which lacked tall ferns. There were many opportunities for conifer establishment, with high seedling densities recorded on the forest floor and on logs. By contrast, angiosperm seedlings were mainly restricted to logs. 5 Our results suggest that several mechanisms act in concert to reduce regeneration opportunities for conifers in productive habitats. In particular, we suggest that tall ferns and deep shade are responsible for a restriction of regeneration opportunities in relatively productive forests in New Zealand, diminishing the opportunities for conifers to escape the competitive effects of fast-growing angiosperms. Thus ‘crocodiles’ may alter the outcome of the race between ‘hares’ and ‘tortoises’. [ABSTRACT FROM AUTHOR]