Improving Trapping Efficiency for Control of American Mink (Neovison vison) in Patagonia

Two main challenges when controlling alien American mink (Neovison vison) in Patagonia are to maximize campaign efficacy and cost-effectiveness and to avoid trapping native species. We designed and tested new variants of collapsible wire box traps, compared the efficacy of a food-based bait and a scent lure and compared catch rates in different seasons of the year. We used the data to model the efficiency rate of the trapping and to determine the trapping effort required to remove 70-90% of the estimated discrete mink population. Between January 2018 and March 2021, we operated 59 trapping transects over 103 three-day trapping periods in southern Chile. Traps were first baited with canned fish, and afterwards with mink anal gland lure. We compared the efficacy of mink capture with that of our previous study. We trapped 196 mink (125 males, 71 females), with most captures in summer. The medium-sized GMV-18 trap caught more male mink, but the more compact GMV-13 caught fewer non-target rodents and no native mammals. The scent lure was more successful than the canned fish when the previous campaign's data were included in the analysis. There was also a significant improvement in the proportion of female mink trapped and reduced labour compared with our previous campaign that used larger traps, fish bait and 400-500 m trap spacings. We caught relatively more females than males after the third night of trapping on a transect. Our data analysis supports the use of the GMV-13 variant of wire cage trap as the best trap size: it is effective on female mink, small, cheap and easy to transport. Combined with mink anal scent lure, it reduces the possibility of trapping native species compared with other traps tested in Chile. As the most efficient method for removing at least 70% of the estimated discrete mink population within the area covered by each trap transect in southern Chile tested to date, we recommend trapping campaigns using GMV-13 during summer, with a 200-m trap spacing, for up to 6 days before moving traps to a new site, with a combination of three days with a female scent gland lure, followed by three days with a male scent gland lure.

Modeling herbivore functional responses causing boom-bust dynamics following predator removal

Native biodiversity is threatened by invasive species in many terrestrial and marine systems, and conservation managers have demonstrated successes by responding with eradication or control programs. Although invasive species are often the direct cause of threat to native species, ecosystems can react in unexpected ways to their removal or reduction. Here, we use theoretical models to predict boom-bust dynamics, where the removal of predatory or competitive pressure from a native herbivore results in oscillatory population dynamics (boom-bust), which can endanger the native species' population in the short term. We simulate control activities, applied to multiple theoretical three-species Lotka-Volterra ecosystem models consisting of vegetation, a native herbivore, and an invasive predator. Based on these communities, we then develop a predictive tool that-based on relative parameter values-predicts whether control efforts directed at the invasive predator will lead to herbivore release followed by a crash. Further, by investigating the different functional responses, we show that model structure, as well as model parameters, are important determinants of conservation outcomes. Finally, control strategies that can mitigate these negative consequences are identified. Managers working in similar data-poor ecosystems can use the predictive tool to assess the probability that their system will exhibit boom-bust dynamics, without knowing exact community parameter values.

Responses of New Zealand forest birds to management of introduced mammals

Over the past 1000 years New Zealand has lost 40-50% of its bird species, and over half of these extinctions are attributable to predation by introduced mammals. Populations of many extant forest bird species continue to be depredated by mammals, especially rats, possums, and mustelids. The management history of New Zealand's forests over the past 50 years presents a unique opportunity because a varied program of mammalian predator control has created a replicated management experiment. We conducted a meta-analysis of population-level responses of forest birds to different levels of mammal control recorded across New Zealand. We collected data from 32 uniquely treated sites and 20 extant bird species representing a total of 247 population responses to 3 intensities of invasive mammal control (zero, low, and high). The treatments varied from eradication of invasive mammals via ground-based techniques to periodic suppression of mammals via aerially sown toxin. We modeled population-level responses of birds according to key life history attributes to determine the biological processes that influence species' responses to management. Large endemic species, such as the Kaka (Nestor meridionalis) and New Zealand Pigeon (Hemiphaga novaeseelandiae), responded positively at the population level to mammal control in 61 of 77 cases for species ≥20 g compared with 31 positive responses from 78 cases for species <20 g. The Fantail (Rhipidura fuliginosa) and Grey Warbler (Gerygone igata), both shallow endemic species, and 4 nonendemic species (Blackbird [Turdus merula], Chaffinch [Fringilla coelebs], Dunnock [Prunella modularis], and Silvereye [Zosterops lateralis]) that arrived in New Zealand in the last 200 years tended to have slight negative or neutral responses to mammal control (59 of 77 cases). Our results suggest that large, deeply endemic forest birds, especially cavity nesters, are most at risk of further decline in the absence of mammal control and, conversely suggest that 6 species apparently tolerate the presence of invasive mammals and may be sensitive to competition from larger endemic birds.

Biases in the Detection of Intentionally Poisoned Animals: Public Health and Conservation Implications from a Field Experiment

Intentional poisoning is a global wildlife problem and an overlooked risk factor for public health. Managing poisoning requires unbiased and high-quality data through wildlife monitoring protocols, which are largely lacking. We herein evaluated the biases associated with current monitoring programmes of wildlife poisoning in Spain. We compared the national poisoning database for the 1990-2015 period with information obtained from a field experiment during which we used camera-traps to detect the species that consumed non-poisoned baits. Our findings suggest that the detection rate of poisoned animals is species-dependent: Several animal groups (e.g., domestic mammalian carnivores and vultures) tended to be over-represented in the poisoning national database, while others (e.g., corvids and small mammals) were underrepresented. As revealed by the GLMM analyses, the probability of a given species being overrepresented was higher for heaviest, aerial, and cryptic species. In conclusion, we found that monitoring poisoned fauna based on heterogeneous sources may produce important biases in detection rates; thus, such information should be used with caution by managers and policy-makers. Our findings may guide to future search efforts aimed to reach a more comprehensive understanding of the intentional wildlife poisoning problem.

Minimizing animal welfare harms associated with predation management in agro-ecosystems

The impacts of wild predators on livestock are a common source of human-wildlife conflict globally, and predators are subject to population control for this reason in many situations. Animal welfare is one of many important considerations affecting decisions about predation management. Recent studies discussing animal welfare in this context have presented arguments emphasizing the importance of avoiding intentional harm to predators, but they have not usually considered harms imposed by predators on livestock and other animals. Efforts to mitigate predation impacts (including 'no control' approaches) cause a variety of harms to predators, livestock and other wildlife. Successfully minimizing the overall frequency and magnitude of harms requires consideration of the direct, indirect, intentional and unintentional harms imposed on all animals inhabiting agricultural landscapes. We review the harms resulting from the management of dingoes and other wild dogs in the extensive beef cattle grazing systems of Australia to illustrate how these negative impacts can be minimized across both wild and domestic species present on a farm or in a free-ranging livestock grazing context. Similar to many other predator-livestock conflicts, wild dogs impose intermittent harms on beef cattle (especially calves) including fatal predation, non-fatal attack (mauling and biting), pathogen transmission, and fear- or stress-related effects. Wild dog control tools and strategies impose harms on dingoes and other wildlife including stress, pain and death as a consequence of both lethal and non-lethal control approaches. To balance these various sources of harm, we argue that the tactical use of lethal predator control approaches can result in harming the least number of individual animals, given certain conditions. This conclusion conflicts with both traditional (e.g. continuous or ongoing lethal control) and contemporary (e.g. predator-friendly or no-control) predation management approaches. The general and transferable issues, approaches and principles we describe have broad applicability to many other human-wildlife conflicts around the world.

The influence of different aspects of grouse moorland management on nontarget bird assemblages

Conflict between stakeholders with opposing interests can hamper biodiversity conservation. When conflicts become entrenched, evidence from applied ecology can reveal new ways forward for their management. In particular, where disagreement exists over the efficacy or ethics of management actions, research clarifying the uncertain impacts of management on wildlife can move debates forwards to conciliation.Here, we explore a case-study of entrenched conflict where uncertainty exists over the impacts of multiple management actions: namely, moorlands managed for the shooting of red grouse (willow ptarmigan) Lagopus lagopus in the United Kingdom (UK). Debate over how UK moorlands should be managed is increasingly polarized. We evaluate, for the first time at a regional scale, the relative impacts of two major moorland management practices-predator control and heather burning-on nontarget bird species of conservation concern.Birds were surveyed on 18 estates across Northern England and Southeast Scotland. Sites ranged from intensively managed grouse moors to moorland sites with no management for grouse shooting. We hypothesised that both targeted predator control and burning regimes would enhance ground-nesting wader numbers and, as a consequence of this, and of increased grouse numbers, nontarget avian predators should also be more abundant on heavily managed sites.There were positive associations between predator control and the abundance of the three most widespread species of ground-nesting wader: strong effects for European golden plover Pluvialis apricaria and Eurasian curlew Numenius arquata and, less strongly, for common snipe Gallinago gallinago. These effects saturated at low levels of predator control. Evidence for effects of burning was much weaker. We found no evidence of enhanced numbers of nontarget predators on heavily managed sites.

Cat Gets Its Tern: A Case Study of Predation on a Threatened Coastal Seabird

Domestic cats have a cosmopolitan distribution, commonly residing in urban, suburban and peri-urban environments that are also critical for biodiversity conservation. This study describes the impact of a desexed, free-roaming cat on the behavior of a threatened coastal seabird, the Australian Fairy Tern, Sternula nereis nereis, in Mandurah, south-western Australia. Wildlife cameras and direct observations of cat incursions into the tern colony at night, decapitated carcasses of adult terns, dead, injured or missing tern chicks, and cat tracks and scats around the colony provided strong evidence of cat predation, which led to an initial change in nesting behavior and, ultimately, colony abandonment and the reproductive failure of 111 nests. The death of six breeding terns from the population was a considerable loss for this threatened species and had the potential to limit population growth. This study highlights the significant negative impacts of free-roaming cats on wildlife and the need for monitoring and controlling cats at sites managed for species conservation. It also provides strong evidence against the practice of trap-neuter-release programs and demonstrates that desexed cats can continue to negatively impact wildlife post-release directly through predation, but also indirectly through fundamental changes in prey behavior and a reduction in parental care.

Can multitrophic interactions and ocean warming influence large-scale kelp recovery?

Ongoing changes along the northeastern Atlantic coastline provide an opportunity to explore the influence of climate change and multitrophic interactions on the recovery of kelp. Here, vast areas of sea urchin-dominated barren grounds have shifted back to kelp forests, in parallel with changes in sea temperature and predator abundances. We have compiled data from studies covering more than 1,500-km coastline in northern Norway. The dataset has been used to identify regional patterns in kelp recovery and sea urchin recruitment, and to relate these to abiotic and biotic factors, including structurally complex substrates functioning as refuge for sea urchins. The study area covers a latitudinal gradient of temperature and different levels of predator pressure from the edible crab (Cancer pagurus) and the red king crab (Paralithodes camtschaticus). The population development of these two sea urchin predators and a possible predator on crabs, the coastal cod (Gadus morhua), were analyzed. In the southernmost and warmest region, kelp forests recovery and sea urchin recruitment are mainly low, although sea urchins might also be locally abundant. Further north, sea urchin barrens still dominate, and juvenile sea urchin densities are high. In the northernmost and cold region, kelp forests are recovering, despite high recruitment and densities of sea urchins. Here, sea urchins were found only in refuge habitats, whereas kelp recovery occurred mainly on open bedrock. The ocean warming, the increase in the abundance of edible crab in the south, and the increase in invasive red king crab in the north may explain the observed changes in kelp recovery and sea urchin distribution. The expansion of both crab species coincided with a population decline in the top-predator coastal cod. The role of key species (sea urchins, kelp, cod, and crabs) and processes involved in structuring the community are hypothesized in a conceptual model, and the knowledge behind the suggested links and interactions is explored.

Spatial processes decouple management from objectives in a heterogeneous landscape: predator control as a case study

Predator control is often implemented with the intent of disrupting top-down regulation in sensitive prey populations. However, ambiguity surrounding the efficacy of predator management, as well as the strength of top-down effects of predators in general, is often exacerbated by the spatially implicit analytical approaches used in assessing data with explicit spatial structure. Here, we highlight the importance of considering spatial context in the case of a predator control study in south-central Utah. We assessed the spatial match between aerial removal risk in coyotes (Canis latrans) and mule deer (Odocoileus hemionus) resource selection during parturition using a spatially explicit, multi-level Bayesian model. With our model, we were able to evaluate spatial congruence between management action (i.e., coyote removal) and objective (i.e., parturient deer site selection) at two distinct scales: the level of the management unit and the individual coyote removal. In the case of the former, our results indicated substantial spatial heterogeneity in expected congruence between removal risk and parturient deer site selection across large areas, and is a reflection of logistical constraints acting on the management strategy and differences in space use between the two species. At the level of the individual removal, we demonstrated that the potential management benefits of a removed coyote were highly variable across all individuals removed and in many cases, spatially distinct from parturient deer resource selection. Our methods and results provide a means of evaluating where we might anticipate an impact of predator control, while emphasizing the need to weight individual removals based on spatial proximity to management objectives in any assessment of large-scale predator control. Although we highlight the importance of spatial context in assessments of predator control strategy, we believe our methods are readily generalizable in any management or large-scale experimental framework where spatial context is likely an important driver of outcomes.

Factors that influence vital rates of Seaside and Saltmarsh sparrows in coastal New Jersey, USA

As saltmarsh habitat continues to disappear, understanding the factors that influence saltmarsh breeding bird population dynamics is an important step for the conservation of these declining species. Using five years (2011 - 2015) of demographic data, we evaluated and compared Seaside (Ammodramus maritimus) and Saltmarsh (A. caudacutus) sparrow apparent adult survival and nest survival at the Edwin B. Forsythe National Wildlife Refuge, New Jersey, USA. We determined the effect of site management history (unditched vs. ditched marsh) on adult and nest survival to aid in prioritizing future management or restoration actions. Seaside Sparrow apparent adult survival (61.6%, 95% CI: 52.5 - 70.0%) averaged >1.5 times greater than Saltmarsh Sparrow apparent adult survival (39.9%, 95% CI: 34.0 - 46.2%). Nest survival and predation and flooding rates did not differ between species, and predation was the primary cause of failure for both species. Apparent adult survival and nest survival did not differ between unditched and ditched marshes for either species, indicating that marsh ditching history may not affect breeding habitat quality for these species. With predation as the primary cause of nest failure for both species in New Jersey, we suggest that future research should focus on identification of predator communities in salt marshes and the potential for implementing predator-control programs to limit population declines.

Landscape genetics of the nonnative red fox of California

Invasive mammalian carnivores contribute disproportionately to declines in global biodiversity. In California, nonnative red foxes (Vulpes vulpes) have significantly impacted endangered ground‐nesting birds and native canids. These foxes derive primarily from captive‐reared animals associated with the fur‐farming industry. Over the past five decades, the cumulative area occupied by nonnative red fox increased to cover much of central and southern California. We used a landscape‐genetic approach involving mitochondrial DNA (mtDNA) sequences and 13 microsatellites of 402 nonnative red foxes removed in predator control programs to investigate source populations, contemporary connectivity, and metapopulation dynamics. Both markers indicated high population structuring consistent with origins from multiple introductions and low subsequent gene flow. Landscape‐genetic modeling indicated that population connectivity was especially low among coastal sampling sites surrounded by mountainous wildlands but somewhat higher through topographically flat, urban and agricultural landscapes. The genetic composition of populations tended to be stable for multiple generations, indicating a degree of demographic resilience to predator removal programs. However, in two sites where intensive predator control reduced fox abundance, we observed increases in immigration, suggesting potential for recolonization to counter eradication attempts. These findings, along with continued genetic monitoring, can help guide localized management of foxes by identifying points of introductions and routes of spread and evaluating the relative importance of reproduction and immigration in maintaining populations. More generally, the study illustrates the utility of a landscape‐genetic approach for understanding invasion dynamics and metapopulation structure of one of the world's most destructive invasive mammals, the red fox.

The Selective Use of Hypochlorite to Prevent Pond Crashes for Algae-Biofuel Production

Although algae-biofuels have many advantages including high areal productivity, algae can be preyed upon by amoebas, protozoans, ciliates, and rotifers, particularly in open pond systems. Thus, these higher organisms need to be controlled. In this study, Chlorella kessleri was used as the algal culture and Brachionus calyciflorus as the source of predation. The effect of sodium hypochlorite (bleach) was tested with the goal of totally inhibiting the rotifer while causing minor inhibition to the alga. The 24-hr LC50 for B. calyciflorus in spring water was 0.198 mg Cl/L while the 24-hr LC50 for C. kessleri was 0.321 mg Cl/L. However, chlorine dissipates rapidly as the algae serves as reductant. Results showed a chlorine dosage between 0.45 to 0.6 mg Cl/L and a dosing interval of two hours created the necessary chlorine concentrations to inhibit predation while letting the algae grow; thus giving algae farmers a tool to prevent pond crashes. Water Environ. Res., 87 (2015).

Competition on the range: science vs. perception in a bison-cattle conflict in the western USA

Competition between livestock and wild ungulates is commonly perceived to occur on shared rangelands. In the Henry Mountains (HM) of Utah, a free‐ranging population of bison Bison bison has raised concerns among ranchers holding grazing permits on these public lands. Bison are the most conspicuous potential competitors with cattle, but lagomorphs (mainly jackrabbits Lepus californicus) are also abundant in this area. The local ranching community is applying political pressure on state and federal agencies to resolve ‘the bison problem’, but the relative grazing impacts of bison, cattle and lagomorphs have not previously been quantified.

We constructed 40 grazing exclosures (each 5·95 m²) in the conflict area: 20 excluded bison + cattle (‘partial’) and 20 excluded bison + cattle + lagomorphs (‘full’). All exclosures, each with a paired open reference plot, were monitored for 1 year, and above‐ground plant production was measured. GPS telemetry (bison) and scheduled grazing (cattle) allowed visitation to be quantified for each ungulate species based on the number of ‘animal days’ in the area. Rancher perceptions of wildlife–cattle interactions were recorded in a questionnaire survey.

Ranchers perceived bison as a high‐level competitor with cattle, whereas lagomorphs were perceived as low‐level competitors.

Grazed reference plots yielded an average (±SE) of 22·7 g m⁻² (±5·16) of grass, compared to 36·5 g m⁻² (±7·33) in the partial exclosures and 43·7 g m⁻² (±7·61) in the full exclosures. Exclusion of large herbivores thus resulted in a 13·8 g m⁻² increase in grass biomass relative to the reference plots (P = 0·005), with the additional exclusion of lagomorphs resulting in a further 7·18 g m⁻² increase (P = 0·048).

Overall, lagomorphs accounted for 34·1%, bison 13·7% and cattle 52·3% of the total grass biomass removed by all herbivores on the shared range.

Synthesis and applications. Cattle face a greater competitive challenge from lagomorphs than from bison in the study area. This case study illustrates the need for science‐based management of social–ecological systems in which even long‐term resource users might underestimate the complexities of trophic interactions. Attention should be redirected at the lagomorphs and their main predators, coyotes Canis latrans, which are currently subject to population control. To reduce negative perceptions among local ranchers, options should be explored to incorporate benefit‐sharing into the management of the bison population.

Cattle face a greater competitive challenge from lagomorphs than from bison in the study area. This case study illustrates the need for science‐based management of social–ecological systems in which even long‐term resource users might underestimate the complexities of trophic interactions. Attention should be redirected at the lagomorphs and their main predators, coyotes Canis latrans, which are currently subject to population control. To reduce negative perceptions among local ranchers, options should be explored to incorporate benefit‐sharing into the management of the bison population.

Editor's Choice

Strategic rat control for restoring populations of native species in forest fragments

Forest fragments have biodiversity value that may be enhanced through management such as control of non-native predators. However, such efforts may be ineffective, and research is needed to ensure that predator control is done strategically. We used Bayesian hierarchical modeling to estimate fragment-specific effects of experimental rat control on a native species targeted for recovery in a New Zealand pastoral landscape. The experiment was a modified BACI (before-after-control-impact) design conducted over 6 years in 19 forest fragments with low-density subpopulations of North Island Robins (Petroica longipes). The aim was to identify individual fragments that not only showed clear benefits of rat control, but also would have a high probability of subpopulation growth even if they were the only fragment managed. We collected data on fecundity, adult and juvenile survival, and juvenile emigration, and modeled the data in an integrated framework to estimate the expected annual growth rate (λ) of each subpopulation with and without rat control. Without emigration, subpopulation growth was estimated as marginal (λ = 0.95-1.05) or negative (λ = 0.74-0.90) without rat control, but it was estimated as positive in all fragments (λ = 1.4-2.1) if rats were controlled. This reflected a 150% average increase in fecundity and 45% average increase in adult female survival. The probability of a juvenile remaining in its natal fragment was 0.37 on average, but varied with fragment connectivity. With juvenile emigration added, 6 fragments were estimated to have a high (>0.8) probability of being self-sustaining (λ > 1) with rat control. The key factors affecting subpopulation growth rates under rat control were low connectivity and stock fencing because these factors were associated with lower juvenile emigration and higher fecundity, respectively. However, there was also substantial random variation in adult survival among fragments, illustrating the importance of hierarchical modeling for fragmentation studies.

Livestock husbandry as a tool for carnivore conservation in Africa’s community rangelands: a case–control study

Conflict between people and wildlife is a major issue in both wildlife conservation and rural development. In African rangelands, species such as African wild dogs (Lycaon pictus), cheetahs (Acinonyx jubatus), lions (Panthera leo), leopards (Panthera pardus), and spotted hyaenas (Crocuta crocuta) may kill livestock and are therefore themselves killed by local pastoralists. Such conflict has led to the extirpation of these species from many areas, and also impacts the livelihoods of local livestock farmers. To investigate the possibilities for coexistence of people, livestock, and large predators in community rangelands, we measured the effectiveness of traditional livestock husbandry in reducing depredation by wild carnivores, using a case–control approach. Different measures were effective against different predator species but, overall, the risk of predator attack by day was lowest for small herds, accompanied by herd dogs as well as human herders, grazing in open habitat. By night, the risk of attack was lowest for herds held in enclosures (‘bomas’) with dense walls, pierced by few gates, where both men and domestic dogs were present. Unexpectedly, the presence of scarecrows increased the risks of attack on bomas. Our findings suggest that improvements to livestock husbandry can contribute to the conservation and recovery of large carnivores in community rangelands, although other measures such as prey conservation and control of domestic dog diseases are also likely to be necessary for some species.