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Context. Precise and accurate methods are essential to assess wildlife populations for sound management. We surveyed a managed population of fallow deer (Dama dama) in a Mediterranean environment in Italy, where this non-native ungulate has a negative impact on biodiversity.
Aims. We compare nocturnal distance-sampling (deer are detected by thermal imagery at night) population estimates with demographic projections of the same population.
Methods. We estimated natural survival in fawns (0.86), yearlings (0.83), adult males (0.70) and adult females (0.90) using capture–mark–recapture. By integrating survival estimates with population structure, reproductive traits and harvest data, we performed demographic projections. We performed nocturnal distance sampling on foot by using a thermal imagery once a year (in autumn) from 2001 to 2005. We walked 75–77 km (71 transects) per each survey.
Key results. We showed that our survey design met distance-sampling assumptions. Distance sampling and demographic projections yielded similar and precise (12.6% < CV <24.1%) population estimates, showing a decreasing (–164.64 deer year–1) population trend from 2755 deer in 2001 to 1877 in 2005.
Conclusions. We showed that nocturnal distance sampling is useful to monitor wild deer populations in forests effectively and that it represents a cost-effective tool to develop sounded management policy for this non-native species. We also provided, for the first time, a comprehensive stochastic population model for fallow deer in a Mediterranean environment. Using these population estimates, managers could reduce fallow deer population size to a level compatible with the conservation of the endangered Italian roe deer and improve forest regeneration.
Implications. Nocturnal distance sampling can be used to assess ungulate population living in dense forested habitats effectively and efficiently.
David M. Forsyth, David S. L. Ramsey, Clare J. Veltman, Robert B. Allen, Will J. Allen, Richard J. Barker, Chris L. Jacobson, Simon J. Nicol, Sarah J. Richardson, Charles R. Todd
Context. When environmental, economic and/or social effects of wildlife are considered undesirable and need to be reduced, managers require knowledge of the effectiveness of candidate control techniques, particularly the relationship between control effort and change in abundance.
Aims. We evaluated the effects of control on the abundances of introduced red deer (Cervus elaphus scoticus) and sika deer (Cervus nippon) at three New Zealand forest sites (two North Island, one South Island) in an 8-year adaptive-management experiment.
Methods. We identified paired areas of 3600 ha at each site that were as similar as possible in geology, physical environments and forest composition and applied deer control (helicopter- and/or ground-based hunting) to a randomly selected member of each pair. The abundances of deer were monitored in each treatment and non-treatment area for up to 7 years by using faecal pellet counts on 50 randomly located transects.
Key results. The difference between deer abundances in the treatment and non-treatment areas was significantly negative at one site, significantly positive at one site and indistinguishable at the other site. Faecal pellet abundances declined with increasing helicopter-based hunting effort but did not change with increasing ground-based hunting effort. There was evidence that aerially sown 1080 baits used for possum control in two treatment areas reduced deer abundances.
Conclusions. The substantial uncertainty surrounding the relationships between deer control effort and changes in deer abundance means that managers cannot assume that the environmental, economic and/or social problems caused by deer will be alleviated with the quantum of control effort applied in the present study.
Implications. Reducing the abundances of deer in forests may require substantially more control effort than is currently believed.
Context. The feral pig (Sus scrofa) is a widespread pest species in Australia and its populations are commonly controlled to reduce damage to agriculture and the environment. Feral pigs are also a resource and harvested for commercial export as game meat. Although many other control techniques are used, commercial harvesting of feral pigs is often encouraged by land managers, because it carries little or no cost and is widely perceived to control populations.
Aims. To use feral-pig harvesting records, density data and simple harvest models to examine the effectiveness of commercial harvesting to reduce feral-pig populations.
Methods. The present study examined commercial harvest off-take on six sites (246–657 km2) in southern Queensland, and 20 large blocks (∼2–6000 km2) throughout Queensland. The harvest off-take for each site was divided by monthly or average annual population size, determined by aerial survey, to calculate monthly and annual harvest rates. A simple harvest model assuming logistic population growth was used to determine the likely effectiveness of harvesting.
Key results. Commercial harvest rates were generally low (<∼20%) and are likely to provide only modest reductions in population size. Additionally, harvest rates capable of substantial reductions (>50%) in long-term population size were isolated occurrences and not maintained across sites and years. High harvest rates were observed only at low densities. Although these harvest rates may be sufficiently high to hold populations at low densities, the population is likely to escape this entrapment following a flush in food supply or a reduction in harvest effort.
Implications. Our results demonstrated that, at current harvest rates, commercial harvesting is ineffective for the landscape-scale control of feral-pig populations. Unless harvest rates can be significantly increased, commercial harvesting should be used as a supplement to, rather than as a substitute for, other damage-control techniques.
Context. Selective logging of native forests creates a mosaic of disturbance histories; however, little is known about how different taxa respond to such a mosaic.
Aims. We followed adaptive-management principles to test logging and burning impacts on eastern pygmy possums, Cercartetus nanus (Geoffroy and Desmarest, 1817), by undertaking a large-scale field experiment that coincided with harvesting. We predicted that home range would increase after logging because of a reduction in resources (food and/or dens) and because hollows suitable for denning would decrease, resulting in greater use of unlogged patches and alternate dens.
Methods. We radio-tracked C. nanus in a before-and-after logging experiment to investigate home range, habitat selection and den use. We tracked 50 possums, some individuals for a maximum of 8 months, within control, recently logged and regrowth (5 years since logging) sites.
Key results. Home ranges were variable (0.04–19.5 ha), with males having significantly larger home ranges. We were unable to detect a difference in home-range size between controls and the first year after logging and burning, or regrowth 5 years after logging. Home ranges comprised a mosaic of disturbed and undisturbed areas, and possums did not avoid logged habitat in their home ranges, indicating that logging did not significantly influence habitat selection. We suggest that possums were not sensitive to selective logging and burning because nectar-producing plants are adapted to fire disturbance and because a variety of den sites were used, most commonly in tree hollows and fallen logs, which were commonly left as logging residue. Indeed, possums frequently denned in logged patches, both recently after logging (63% of dens) and in regrowth 5 years after logging (76% of dens). Counts of fallen hollow logs at each site indicated that their density was not reduced by logging, with regrowth sites having the greatest abundance of logs (260 ha–1).
Conclusions. The mosaic of disturbance created by selective logging operations did not negatively affect home range or den selection of C. nanus.
Implications. Ecologically sustainable logging practices that include a range of mitigation measures to protect biodiversity can be compatible with the management of threatened species. Assessment of the effectiveness of these methods often will rely on scientific research.
Context. Avian–human conflict is a growing issue in urban areas, yet studies of conflict tend to be species and situation specific and focus on landscape characteristics that generate or exacerbate the problem.
Aims. To determine characteristics of bird species that cause conflict in urban areas within their native range and to develop a model that can be used to assess the relative likelihood of a New Zealand species causing conflict in the future.
Methods. Ecological, behavioural and life-history characteristics of 33 conflict-causing species identified from the literature and 106 randomly selected non-conflict congeners were compared using an information-theoretic approach to multi-model selection and inference. Variables from the confidence set of models were used to develop a model that was applied to the New Zealand urban avifauna to provide a relative measure of a species’ potential to generate conflict.
Key results. A model including only dietary breadth best explained the conflict (ωi = 0.833). Using dietary breadth, flocking, clutch size, granivory, territoriality and non-ground nesting – the confidence model set – New Zealand’s native pukeko (Porphyrio porphyria), red-billed gull, (Larus scopulinus), and kākā (Nestor meridionalis) were identified as the three species most likely to generate conflict with urban residents.
Conclusions. Broad dietary requirements may allow a species to take advantage of novel and varied food sources in the urban environment and lead to population growth. Large populations at high density may amplify problems, exceeding residents’ tolerance levels and resulting in conflict. Species characteristics relating to nesting, sociality and body size were found to be uninformative.
Implications. Species with a broad diet, particularly those identified by this study as having a high potential for conflict, should be the focus of monitoring to identify population growth and the emergence of problems in urban areas. This will allow proactive implementation of management, improving the likelihood of conflict mitigation.
Context. In metapopulations, colonisation is the result of dispersal from neighbouring occupied patches, typically juveniles dispersing from natal to breeding sites. When occupancy dynamics are dispersal driven, occupancy should refer to the presence of established, breeding populations. The detection of transient individuals at sites that are, by definition, unoccupied (i.e. false positive detections), may result in misleading conclusions about metapopulation dynamics. Until recently, the issue of false positives has been considered negligible and current efforts to account for such error have been restricted to the context of species misidentification. However, the detection of transient individuals visiting multiple sites while dispersing is a distinct source of false positives that can bias estimates of occupancy because visited sites do not contribute to metapopulation dynamics in the same way as do sites occupied by established, reproducing populations. Although transient-induced false positive error presents a challenge to occupancy studies aiming to account for all sources of detection error and estimate occupancy without bias, accounting for it has received little attention.
Aims. Using a novel application of an existing occupancy model, we sought to account for false positives that result from transient individuals being observed at truly unoccupied sites (i.e. where no establishment has occurred).
Methods. We applied a Bayesian multi-season occupancy model correcting for false negative and false positive errors, to 3 years of detection or non-detection data from a metapopulation of water voles, Arvicola amphibious, in which both types of patch-state misclassification are suspected.
Key results. We provide evidence that transient individuals can cause false positive detection errors. We then demonstrate the flexibility of the occupancy model to account for both false negative and false positive detection errors beyond the typical application to species misidentification. Accounting for both types of observation error reduces the bias in estimates of occupancy and avoids misleading conclusions about the status of (meta) populations by allowing for the distinction to be made between resident and transient occupancy.
Conclusion. In many species, transience may result in patch-state misclassification which needs to be accounted for so as to draw correct inference about metapopulation status. Making the distinction between occupancy by established populations and visitation by transients will influence how we interpret patch occupancy dynamics, with important implications for the management of wildlife.
Implications. The ability to estimate occupancy free of bias induced by false positive detections can help ensure that downward trends in occupancy are detected despite such declines being accompanied by increasing frequency of transients associated with, for example, reductions in mate availability or failure to establish. Our approach can be applied to any occupancy study in which false positive detections are suspected because of the behaviour of the focal species.
Context. A main goal of conservation is to mitigate anthropogenic impacts on natural ecosystems, thus conservation tools themselves should not negatively affect target species. Predator-exclusion cages are effectively used to reduce predation of turtle nests; however, their effects on nest environment and developing hatchlings have not been examined.
Aims. Our study had the following four goals: (1) to examine effects of cages on the nest environment, (2) determine whether nest caging affects proxies for hatchling fitness, (3) evaluate whether nest predators preferentially interact with certain cage types, and (4) assess the cost-effectiveness of different nest caging designs.
Methods. In 2010 and 2011 in Algonquin Provincial Park, Ontario, painted turtle (Chrysemys picta; n = 93) and snapping turtle (Chelydra serpentina; n = 91) nests were assigned to one of three treatments (wooden-sided cages, above- and below-ground wire cages) or a control (no nest cage) and outfitted with a data logger to record incubation temperature. After emergence, hatching success and proxies of hatchling fitness were measured.
Key results. Nest temperature, hatching success, frequency of hatchling deformities and locomotor performance did not differ among cage treatments. However, hatchling body condition differed among treatments; wooden-sided and below-ground cages had the most positive influence on body condition in painted and snapping turtles, respectively. Predator interactions did not differ among treatments, and wooden-sided cages were the most inexpensive to construct.
Conclusions. Nest cages did not alter the nest environment from natural conditions but did alter hatchling body condition, and nest caging affected species differently.
Implications. Nest cages are known to reduce nest depredation, and our data indicated that, in general, nest cages also do not affect the nest environment or proxies for hatchling fitness. Thus, our findings indicated that cages are effective conservation tools that do not present secondary deleterious effects on potential recruitment.
Context. Roads have numerous impacts on wildlife populations, such as forming barriers to movement and isolating them from resources. However, knowledge of how wildlife behave in road-impacted environments is limited.
Aims. Our aim was to assess the suitability of roadside habitat for the swamp wallaby (Wallabia bicolor).
Methods. We measured the home range, habitat use and body metrics of swamp wallabies at two roadside locations. The home ranges and fitness of the roadside wallabies were compared with the metrics of swamp wallabies within the adjacent reserve.
Key results. The roadside wallabies had a preference for canopy cover, but not for other habitat features. The roadside home ranges were stable and relatively small. The nocturnal ranges were considerably smaller and further from the road than were diurnal ranges. Only one wallaby crossed the road during the study, via an underpass. There was a significant positive linear correlation between pes length and bodyweight. Roadside wallabies were significantly heavier than were reserve wallabies.
Conclusions. Our study suggested that individual wallabies avoid the road, are habituated to the roadside environment and may even benefit from it. At the very least, roadside habitats are adequate for the swamp wallaby.
Implications. Fencing and road crossings are likely to be beneficial conservation-management measures for swamp wallabies in roadside reserves.
Context. Farmland crops may suffer damage from native animals, but also provide a critical resource during times of food scarcity. We know little about bird use of almond crops.
Aims. To examine factors influencing temporal and spatial variation in the use of almond crops in north-western Victoria by bird species, including the threatened regent parrot (Polytelis anthopeplus), and to record levels of crop damage.
Methods. We measured bird occurrence in 15 transects during the almond-growing season of 2009/10, and 32 transects during 2010/11. Crop-damage assessments were conducted in 2010/11. Spatio-temporal variation in bird occurrence was related to seasonal factors, landscape variables and bird-control activities.
Key results. Significantly more regent parrots and small parrots (e.g. Platycercus elegans and Psephotus haematonotus) were recorded in almond plantations in 2009/10 than in 2010/11. Rainfall and wheat production was much higher in 2010/11, and we hypothesise that the availability of alternative foods reduced parrot dependence on almonds. Regent parrot occurrence did not differ across months within a season, but more small parrots were recorded during almond nut maturity. Regent parrots appeared to prefer locations where almond crops abutted native vegetation, but only during 2009/10, a dry year with likely limited food availability. Small parrots occurred more often in crops close to riverine vegetation and distant from farm offices. Nut damage was generally low, with only 7 of 32 transects sustaining >4% total damage, but damage assessments were conducted during a season of high rainfall, with likely greater availability of alternative food. Percentage damage was significantly correlated with the number of regent and small parrots. Shooting activity did not deter birds from using almond crops.
Conclusions. Parrots appear to rely more on almond crops for food when environmental conditions limit other food resources. A key strategy for managing bird impacts on almonds while supporting species conservation is to provide decoy crops of preferred native plants.
Implications. Rapid loss of almond plantations may lead to population declines in the threatened regent parrot if the availability of alternative food is not simultaneously increased. The role of production land uses in supporting native birds needs to be recognised by conservation management agencies.
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