Invasive species are frequently the target of eradication or control programmes to mitigate their impacts. However, manipulating single species in isolation can lead to unexpected consequences for other species, with outcomes such as mesopredator release demonstrated both theoretically and empirically in vertebrate assemblages with at least two trophic levels. Less is known about the consequences of species removal in more complex assemblages where a greater number of interacting invaders increases the potential for selective species removal to result in unexpected changes in community structure. Using a replicated Before-After Control-Impact field experiment with a four-species assemblage of invasive mammals we show that species interactions in the community are dominated by competition rather than predation. There was no measurable response of two mesopredators (rats and mice) following control of the top predator (stoats), but there was competitive release of rats following removal of a herbivore (possums), and competitive release of mice following removal of rats.

Identifying species occupying an area is essential for many ecological and conservation studies. Faecal DNA is a potentially powerful method for identifying cryptic mammalian species. In New Zealand, 10 species of ungulate (Order: Artiodactyla) have established wild populations and are managed as pests because of their impacts on native ecosystems. However, identifying the ungulate species present within a management area based on pellet morphology is unreliable. We present a method that enables reliable identification of 10 ungulate species (red deer, sika deer, rusa deer, fallow deer, sambar deer, white-tailed deer, Himalayan tahr, Alpine chamois, feral sheep, and feral goat) from swabs of faecal pellets. A high resolution melting (HRM) assay, targeting a fragment of the 12S rRNA gene, was developed. Species-specific primers were designed and combined in a multiplex PCR resulting in fragments of different length and therefore different melting behaviour for each species. The method was developed using tissue from each of the 10 species, and was validated in blind trials. Our protocol enabled species to be determined for 94% of faecal pellet swabs collected during routine monitoring by the New Zealand Department of Conservation. Our HRM method enables high-throughput and cost-effective species identification from low DNA template samples, and could readily be adapted to discriminate other mammalian species from faecal DNA.

All capture methods impose animal welfare impacts, but these impacts are rarely quantified or reported. We present data from two wildlife capture studies that trialled new methods for capturing Bennett’s wallabies (Notamacropus rufogriseus) and red deer (Cervus elaphus) in New Zealand. We used helicopter net-gunning for both species, and compared this method with ground-based netting for wallabies and helicopter darting for red deer, using, for the first time in New Zealand, the fast-acting opioid thiafentanil. Efficacy and animal welfare parameters quantified were duration of handling and recovery, and frequency of adverse events, including escape, injury, and mortality. Cost-effectiveness was quantified for each method. Capture mortalities occurred for all methods for both species. For red deer, chemical immobilisation led to fewer traumatic injuries and fewer mortalities, while for wallabies, net-gunning led to fewer mortalities. Net-gunning was an efficient capture method for deer in open habitat, but led to the escape of 54% of wallabies and one wallaby mortality (4%). Ground-based netting resulted in the mortality of 17% of wallabies at the time of capture, and the capture of non-target species. The cost per captured wallaby was 40% more expensive for net-gunning (NZ$1045) than for ground-based netting (NZ$745), but, once corrected for mortalities at the time of capture and suitability of individuals for GPS-collar deployment, this was reduced to 29% and 12% more expensive, respectively. Net-gunning for red deer resulted in the escape of 13% of animals and mortality of 10% of animals at the time of capture. Helicopter-based darting for red deer using thiafentanil (c. 0.03–0.06 mg/kg) had high capture efficacy (zero escapes), rapid induction times (mean of 3 min), and a low mortality rate at 14 days post-capture (3%), but it was more expensive per deer captured and collared than aerial netting (NZ$2677 and NZ$2234, respectively). We recommend reporting of adverse event data for all wildlife capture techniques to permit continual refinement of field methods.

Sentinel species are increasingly used by disease managers to detect and monitor the prevalence of zoonotic diseases in wildlife populations. Characterizing home-range movements of sentinel hosts is thus important for developing improved disease surveillance methods, especially in systems where multiple host species co-exist. We studied ranging activity of major hosts of bovine tuberculosis (TB) in an upland habitat of New Zealand: we compared home-range coverage by ferrets (Mustela furo), wild deer (Cervus elaphus), feral pigs (Sus scrofa), brushtail possums (Trichosurus vulpecula) and free-ranging farmed cattle (Bos taurus). We also report in detail the proportional utilization of a seasonal (4-monthly) range area for the latter four species. Possums covered the smallest home range (<30 ha), ferrets covered ~100 ha, pigs ~4 km(2), deer and cattle both >30 km2. For any given weekly period, cattle, deer and pigs were shown to utilize 37–45% of their estimated 4-month range, while possums utilized 62% during any weekly period and 85% during any monthly period of their estimated 4-month range. We suggest that present means for estimating TB detection kernels, based on long-term range size estimates for possums and sentinel species, probably overstate the true local surveillance coverage per individual.

In New Zealand, bovine tuberculosis (bTB) is present in domestic cattle and deer herds primarily as the result of on-going disease transmission from the primary wildlife host, the brushtail possum (Trichosurus vulpecula). However, bTB is also present in other introduced free-ranging mammalian species. Between 1996 and 2007, we conducted a series of studies to determine whether poison control of possum populations would have any effect on the prevalence of Mycobacterium bovis infection in sympatric feral pigs (Sus scrofa). We compared trends in the prevalence of bTB infection in feral pigs in six study areas: possum numbers were reduced in three areas, but not in the other three, effectively providing a thrice-replicated before-after-control-intervention design. Before possum control, the overall prevalence of culture-confirmed M. bovis infection in feral pigs was 16.7-94.4%, depending on area. Infection prevalence varied little between genders but did vary with age, increasing during the first 2-3 years of life but then declining in older pigs. In the areas in which possum control was applied, M. bovis prevalence in feral pigs fell to near zero within 2-3 years, provided control was applied successfully at the whole-landscape scale. In contrast, prevalence changed much less or not at all in the areas with no possum control. We conclude that feral pigs in New Zealand acquire M. bovis infection mainly by inter-species transmission from possums, but then rarely pass the disease on to other pigs and are end hosts. This is in contrast to the purported role of pigs as bTB maintenance hosts in other countries, and we suggest the difference in host status may reflect differences in the relative importance of the oral route of infection in different environments. Despite harbouring M. bovis infection for a number of years, pigs in New Zealand do not sustain bTB independently, but are good sentinels for disease prevalence in possum populations.

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Incidental kills of deer during aerial-1080 poisoning of brushtail possums (Trichosurus vulpecula) using baits containing sodium monofluoroacetate (1080) causes widespread hunter opposition to this control method. We document the deaths of a large number of fallow deer (Dama dama) after aerial-1080 poisoning in the Blue Mountains, Otago. Three deer fitted with radio collars all died during the poisoning. Eight randomly located "search cells" (25-57 ha) were each searched twice. One pig (Sus scrofa), 53 deer, 58 possum, and 20 bird (three native) carcasses were found. Deercarcass density varied widely between cells (2.2-38.6/km 2 ), reflecting differences in deer density but apparently also the amount of ground cover. The total number of deer killed was estimated using Lincoln indices. More fawns were killed than larger adult deer. Comparison with historical harvest data suggested that between two-thirds and three-quarters of the deer present had been killed. This unintended by-kill will have reduced deer impacts on native plants and the risk of Tb spread or persistence in deer. However, such incidental benefits may not offset the increased indirect "social" costs likely to arise from increased hunter opposition to use of aerial-1080 poisoning.

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