Exploiting interspecific olfactory communication to monitor predators

Elusive mustelids-18 months in the search of near-threatened stoat (Mustela erminea) and weasel (M. nivalis) reveals low captures

Stoat (Mustela erminea) and weasel (M. nivalis) are hard to monitor as they are elusive of nature and leave few identifying marks in their surroundings. Stoat and weasel are both fully protected in Denmark and are thought to be widely distributed throughout the country. Despite this stoat and weasel were listed on the Danish Red List as Near Threatened in 2019, as their densities and population trends are unknown. Using a modified novel camera trapping device, the Double-Mostela, a wooden box comprising a tracking tunnel and two camera traps, we attempted to obtain density estimates based on identification of individual stoats and weasels. We deployed camera traps both inside Double-Mostela traps and externally in three different study areas in northern Zealand, Denmark, and tested commercial, American scent-based lures to attract stoat and weasel. We obtained very low seasonal trapping rates of weasel in two study areas, but in one study area, we obtained a seasonal trapping rate of stoat larger compared to another study using the Mostela. In one study area, both species were absent. We observed no effect of scent-based lures in attracting small mustelids compared to non-bait traps. Potential reasons behind low capture rates of weasel and stoat are suboptimal habitat placement and timing of deployment of the Double-Mostelas, land-use changes over the last 200 years, predation from larger predators, as well as unintended secondary poisoning with rodenticides. Due to the scarcity of weasel and stoat captures, we were unable to make density estimates based on identification of individuals; however, we identified potential features that could be used for identification and density estimates with more captures.

Niche partitioning in a guild of invasive mammalian predators

Predators compete aggressively for resources, establishing trophic hierarchies that influence ecosystem structure. Competitive interactions are particularly important in invaded ecosystems where introduced predators can suppress native prey species. We investigated whether niche partitioning exists within a guild of invasive mammalian predators and determined the consequences for native species. Over 4405 camera-trap days, we assessed interactions among three invasive predators: two apex predators (feral cats Felis catus and ferrets Mustela furo) and a mesopredator (stoats Mustela erminea), in relation to their primary prey (lagomorphs, rodents and birds) and habitat use. Further, we tested for mesopredator release by selectively removing cats and ferrets in a pulse perturbation experiment. We found compelling evidence of niche partitioning; spatiotemporal activity of apex predators maximized access to abundant invasive prey, with ferrets targeting lagomorphs and cats targeting rodents. Mesopredators adjusted their behavior to reduce the risk of interference competition, thereby restricting access to abundant prey but increasing predation pressure on diurnal native birds. Stoats were only recorded at the treatment site after both larger predators were removed, becoming the most frequently detected predator at 6 months post-perturbation. We suggest there is spatial and resource partitioning within the invasive predator guild, but that this is incomplete, and avoidance is achieved by temporal partitioning within overlapping areas. Niche partitioning among invasive predators facilitates coexistence, but simultaneously intensifies predation pressure on vulnerable native species.

Odour-mediated Interactions Between an Apex Reptilian Predator and its Mammalian Prey

An important but understudied modality for eavesdropping between predators and prey is olfaction, especially between non-mammalian vertebrate predators and their prey. Here we test three olfactory eavesdropping predictions involving an apex reptilian predator, the sand goanna Varanus gouldii, and several species of its small mammalian prey in arid central Australia: 1) small mammals will recognize and avoid the odour of V. gouldii; 2) V. gouldii will be attracted to the odour of small mammals, especially of species that maximize its energetic returns; and 3) small mammals will be less mobile and will show higher burrow fidelity where V. gouldii is absent compared with where it is present. As expected, we found that small mammals recognized and avoided faecal odour of this goanna, feeding less intensively at food patches where the odour of V. gouldii was present than at patches with no odour or a pungency control odour. Varanus gouldii also was attracted to the odour of small mammals in artificial burrows and dug more frequently at burrows containing the odour of species that were energetically profitable than at those of species likely to yield diminishing returns. Our third prediction received mixed support. Rates of movement of three species of small mammals were no different where V. gouldii was present or absent, but burrow fidelity in two of these species increased as expected where V. gouldii had been removed. We conclude that olfaction plays a key role in the dynamic interaction between V. gouldii and its mammalian prey, with the interactants using olfaction to balance their respective costs of foraging and reducing predation risk. We speculate that the risk of predation from this apex reptilian predator drives the highly unusual burrow-shifting behaviour that characterizes many of Australia's small desert mammals.

Fighting ability and the toxicity of raiding pheromone in an obligate kleptoparasite, the stingless bee Lestrimelitta niitkib

Abstract

The evolution of obligate kleptoparasitism, the theft of food, has led to remarkable innovations, including physical weapons and chemical signals that can evolve into chemical weapons. Stingless bees in the genus Lestrimelitta are excellent examples of this phenomenon because they are obligate kleptoparasites that no longer collect floral resources and instead steal brood resources from other bees. Their ability to raid successfully is thus essential to their fitness even when they fight species that are physically bigger, have larger defense forces, or both. We conducted morphometric analyses, quantified Lestrimelitta niitkib mandibular gland pheromone (MGP) components, and carried out individual fighting trials between L. niitkib and the stingless bee Scaptotrigona mexicana, a common victim species, to shed light on the detailed reasons for their success at robbing. Measurements showed that L. niitkib mandibles have thicker exoskeleton cuticles and overall greater width, particularly in the medial and proximal sections, than S. mexicana, which is quite similar in body size. In all fights, L. niitkib bit victims and released MGP, as it does during raids. Scaptotrigona mexicana victims exhibited significantly increased uncoordinated behaviors and showed partial or complete paralysis. We analyzed and quantified the major components of MGP, which consisted of large quantities of geranial (mean of 253 μg) and neral (48 μg) per bee. Microinjections of 1 bee equivalent (BE) of natural or synthetic MGP and ≥ 0.1 BE of geranial significantly increased deleterious behaviors and paralysis as compared to control injections. We suggest that the large quantities of MGP used during raiding have led to an unexpected outcome, a semiochemical evolving the additional function of a toxin, and contribute to the ability of Lestrimelitta to rob its victims.

Significance statement

Kleptoparasites, organisms that steal food resources, employ multiple physical and chemical tools to survive. The success of kleptoparasitism requires a balance between honesty and coercion in interspecific communication. The genus Lestrimellita consists of a group of kleptoparasitic stingless bee species that raid other bee colonies for food and therefore depend upon winning these raids. However, why they succeed remains not fully understood. We studied differences in morphology between L. niitkib and its victims, the pheromones they release during raids, and ran individual fight trials between L. niitkib and a common victim to identify why they are successful. We suggest that the release of pheromones at the beginning of raids, in concert with the pheromone’s toxicity, has been combined to improve L. niitkib’s ability to successfully rob.

Body Odours as Lures for Stoats Mustela erminea: Captive and Field Trials

Simple Summary

The stoat (Mustela erminea) is invasive in New Zealand and has a serious impact on native biota. Trapping is the most common technique used to control stoats, but efforts to eradicate them or to improve control efficiency will require a range of different techniques. We examined the use of mustelid body odours as lures to attract stoats to traps or monitoring devices. Stoats were attracted to stoat urine, scats, and bedding, and to ferret (M. furo) bedding in captive and field trials. The use of odour lures may be particularly useful when the usual food-based lures are ineffective.

Abstract

Eradication and control methods to limit damage caused to native biota in New Zealand by the stoat (Mustela erminea) rely on effective lures for trapping and detection devices, such as cameras. Long-life semiochemical lures have the potential for targeting stoats in situations where food-based lures are of limited success. The attractiveness of body odours of captive stoats was tested in a series of captive animal and extensive field trials to investigate their potential as trapping and monitoring lures. Stoats approached and spent significantly more time sniffing stoat urine and scats and bedding from oestrous female stoats than a non-treatment control. The bedding odours were attractive in both the breeding and the non-breeding season. Stoats also spent significantly more time sniffing oestrous stoat bedding than female ferret bedding, but the ferret odour also produced a significant response by stoats. In the field trials, there were no significant differences between the number of stoats caught with food lures (long-life rabbit or hen eggs) compared with oestrous female or male stoat bedding lures. These results indicate the potential of both stoat bedding odour and the scent of another mustelid species as stoat trapping lures that likely act as a general odour attractant rather than a specific chemical signal of oestrus.

Antipredator responses toward cat fur in wild brown rats tested in a semi-natural environment

Sensitivity to predator-related cues and performance of antipredator behaviors are universal among prey species. Rodents exhibit a diverse suite of antipredator behaviors that have been examined in both field and laboratory studies. However, the results from the laboratory have not always translated to the field. While laboratory studies consistently indicate strong fear-inducing effects of cat fur/skin odors, it is unclear whether this occurs in the field with wild rats. To address this issue, we tested the antipredator responses of wild brown rats (Rattus norvegicus) to predatory (domestic cat fur) and nonpredatory (common brushtail possum fur) odor cues in a semi-natural experimental paradigm. Rats were housed in open air enclosures containing two feeding stations. Following several nights of acclimatization, the feeding stations were paired with cat fur, possum fur, or no fur. Rats spent less time at a feeding station that was paired with cat fur. Duration of time spent at feeding stations increased across consecutive test days and across hours within individual test nights, although the rate of increase within nights was lower for cat fur paired stations. This overall increase might reflect habituation of antipredator behaviors, increasing hunger, or loss of cue potency over time. We suggest that wild brown rats recognize and respond to cat fur odor cues, but their behavioral response is highly adaptable and finely tuned to the trade-off between predation risk and starvation that occurs across short temporal scales.

Baiting/Luring Improves Detection Probability and Species Identification-A Case Study of Mustelids with Camera Traps

Simple Summary

Camera traps are now widely used in animal research because they can monitor animals continuously. Nocturnal mammals are particularly difficult to monitor, and identification without cameras would be difficult. However, camera traps can be improved. We here compared two experimental settings to increase detection and images taken of mustelids, mostly martens. Both tuna bait and glandular scents improved the detection and the number of images taken. Both methods were more successful than a control group setting without any attractants.

Abstract

Motion-triggered trail cameras (hereafter camera traps) are powerful tools which are increasingly used in biological research, especially for species inventories or the estimation of species activity. However, camera traps do not always reliably detect animal visits, as a target species might be too fast, too small, or too far away to trigger an image. Therefore, researchers often apply attractants, such as food or glandular scents, to increase the likelihood of capturing animals. Moreover, with attractants, individuals might remain in front of a camera trap for longer periods leading to a higher number of images and enhanced image quality, which in turn might aid in species identification. The current study compared how two commonly used attractants, bait (tuna) and glandular scent (mustelid mix), affected the detection and the number of images taken by camera traps compared to control camera sites with conventional camera traps. We used a before–after control group design, including a baseline. Attractants increased the probability of detecting the target species and number of images. Tuna experiments produced on average 7.25 times as many images per visit than control camera traps, and scent lures produced on average 18.7 times as many images per visit than the control traps.

Brown rats and house mice eavesdrop on each other's volatile sex pheromone components

Mammalian pheromones often linger in the environment and thus are particularly susceptible to interceptive eavesdropping, commonly understood as a one-way dyadic interaction, where prey sense and respond to the scent of a predator. Here, we tested the “counterespionage” hypothesis that predator and prey co-opt each other’s pheromone as a cue to locate prey or evade predation. We worked with wild brown rats (predator of mice) and wild house mice (prey of brown rats) as model species, testing their responses to pheromone-baited traps at infested field sites. The treatment trap in each of two trap pairs per replicate received sex attractant pheromone components (including testosterone) of male mice or male rats, whereas corresponding control traps received only testosterone, a pheromone component shared between mouse and rat males. Trap pairs disseminating male rat pheromone components captured 3.05 times fewer mice than trap pairs disseminating male mouse pheromone components, and no female mice were captured in rat pheromone-baited traps, indicating predator aversion. Indiscriminate captures of rats in trap pairs disseminating male rat or male mouse pheromone components, and fewer captures of rats in male mouse pheromone traps than in (testosterone-only) control traps indicate that rats do eavesdrop on the male mouse sex pheromone but do not exploit the information for mouse prey location. The counterespionage hypothesis is supported by trap catch data of both mice and rats but only the mice data are in keeping with our predictions for motive of the counterespionage.

Bigger doesn't mean bolder: behavioral variation of four wild rodent species to novelty and predation risk following a fast-slow continuum

Background

Understanding how wild species respond to novel situations with associated risk can provide valuable insights for inter-specific behavioral variation and associations with pace-of-life (POL). Rodents, a globally distributed and diverse taxonomic group, have been the subjects of countless studies emulating risky situations. Controlled laboratory experiments with a focus on wild-caught species provide the opportunity to test fine-scale behavioral responses to contexts of risk with ecological implications. For example, assessing the importance of predator cues eliciting antipredator responses, as well as whether wild rodents embody behavioral plasticity and repertoires, illustrated by habituation and variation in behavioral traits, respectively.

Results

In this comparative study, we examined multiple behavioral responses of four rodent species in eastern Taiwan (three native species Mus caroli, Apodemus agrarius, Rattus losea, and one invasive, Rattus exulans) exposed to an unfamiliar microenvironment and novel cue from an allopatric predator, the leopard cat (Prionailurus bengalensis). All wild-caught animals were subjected to two consecutive nights of experimental trials in a laboratory setting. Behavioral responses to a novel situation during the first trial differed between species; smaller species investing more time in non-defensive behaviors compared to the larger species. More specifically, the smaller species M. caroli and A. agrarius allocated more time to exploration and foraging, whereas the larger rat species R. exulans and R. losea spent more time motionless or concealing. During the second trial, the addition of leopard cat cues did not elicit antipredator behaviors, but rather, rodents were found to exhibit increased non-defensive behaviors, specifically foraging efforts.

Conclusions

Our results suggest that these four species do largely follow a behavioral fast-slow continuum with the two smaller mice species demonstrating increased boldness in a novel context compared to the larger rat species. Also, the wild populations of rodents in eastern Taiwan may be naïve to leopard cats. Finally, the rodents in our study demonstrated habituation to the microenvironment, indicating they possess adaptive capacity.

Leveraging Motivations, Personality, and Sensory Cues for Vertebrate Pest Management

Managing vertebrate pests is a global conservation challenge given their undesirable socio-ecological impacts. Pest management often focuses on the 'average' individual, neglecting individual-level behavioural variation ('personalities') and differences in life histories. These differences affect pest impacts and modify attraction to, or avoidance of, sensory cues. Strategies targeting the average individual may fail to mitigate damage by 'rogues' (individuals causing disproportionate impact) or to target 'recalcitrants' (individuals avoiding standard control measures). Effective management leverages animal behaviours that relate primarily to four core motivations: feeding, fleeing, fighting, and fornication. Management success could be greatly increased by identifying and exploiting individual variation in motivations. We provide explicit suggestions for cue-based tools to manipulate these four motivators, thereby improving pest management outcomes.

Zooming in on mechanistic predator-prey ecology: Integrating camera traps with experimental methods to reveal the drivers of ecological interactions

Camera trap technology has galvanized the study of predator-prey ecology in wild animal communities by expanding the scale and diversity of predator-prey interactions that can be analysed. While observational data from systematic camera arrays have informed inferences on the spatiotemporal outcomes of predator-prey interactions, the capacity for observational studies to identify mechanistic drivers of species interactions is limited. Experimental study designs that utilize camera traps uniquely allow for testing hypothesized mechanisms that drive predator and prey behaviour, incorporating environmental realism not possible in the laboratory while benefiting from the distinct capacity of camera traps to generate large datasets from multiple species with minimal observer interference. However, such pairings of camera traps with experimental methods remain underutilized. We review recent advances in the experimental application of camera traps to investigate fundamental mechanisms underlying predator-prey ecology and present a conceptual guide for designing experimental camera trap studies. Only 9% of camera trap studies on predator-prey ecology in our review use experimental methods, but the application of experimental approaches is increasing. To illustrate the utility of camera trap-based experiments using a case study, we propose a study design that integrates observational and experimental techniques to test a perennial question in predator-prey ecology: how prey balance foraging and safety, as formalized by the risk allocation hypothesis. We discuss applications of camera trap-based experiments to evaluate the diversity of anthropogenic influences on wildlife communities globally. Finally, we review challenges to conducting experimental camera trap studies. Experimental camera trap studies have already begun to play an important role in understanding the predator-prey ecology of free-living animals, and such methods will become increasingly critical to quantifying drivers of community interactions in a rapidly changing world. We recommend increased application of experimental methods in the study of predator and prey responses to humans, synanthropic and invasive species, and other anthropogenic disturbances.

Rapid eradication assessment (REA): a tool for pest absence confirmation

Abstract ContextEradication of invasive species is necessary to protect and assist the recovery of native species and ecosystems. Knowing when to declare an eradication has been successful after ongoing non-detections is a challenge. AimsThe rapid eradication assessment (REA) model is a powerful simulation framework to determine, given model parameters and a fixed level of monitoring effort, the level of confidence in declaring the success of pest eradication. The aim of the present study was to extend the current functionality of the REA model for broader applicability. MethodsThe REA model was advanced so that it was able to account for (1) usage of multiple static device types with different probabilities of detection, (2) incursion detection at a known location and (3) usage of mobile detection devices, which are increasingly being used in conservation. Key resultsAn invasive rat incursion response on Great Mercury Island in New Zealand is used as a comprehensive example to demonstrate the distribution of estimated probability of pest absence among the cases using the current REA model and the extensions presented here. ConclusionsAlthough Great Mercury Island already had a sparse but extensive island-wide network of static biosecurity surveillance devices, and deployed additional static devices around the area of incursion, the greatest improvement in the estimated probability of pest absence following a rat incursion was from additionally using a trained rodent-detection dog. ImplicationsThe added functionality in the REA model and demonstration of its use on a real-world scenario will allow more realistic application by wildlife managers.

An Evaluation of Systematic Versus Strategically-Placed Camera Traps for Monitoring Feral Cats in New Zealand

Simple Summary

Feral cats are detrimental to native biodiversity worldwide. In New Zealand, feral cats are well established across much of the pastoral landscape, including forested areas. Feral cats, like many carnivore species, are elusive in their nature, and often occur at low densities, making them difficult to detect. Camera traps are a useful, non-invasive monitoring device, capable of ‘capturing’ feral cats as they pass by. Although cameras provide a wealth of information about animals within their field of view; there remains much to be learned about optimal camera trap placement within a landscape, if maximizing detection probability is the objective. Here, we report the results of two methods of camera trap deployment within similar sites: (1) systematic deployment on a grid and (2) strategic deployment, predominantly favoring habitats with assumed higher cat activity. Using the Royle–Nichols abundance-induced heterogeneity model (RN), which assumes detection probability and animal abundance are linked, we found that more cats were detected by cameras at forest margins than in mixed scrub or open farmland (but only slightly more than in forest locations). If maximizing cat detections is the aim, we recommend that cameras should be placed at the edges of forests (including forest fragments) whenever feasible.

Abstract

We deploy camera traps to monitor feral cat (Felis catus) populations at two pastoral sites in Hawke’s Bay, North Island, New Zealand. At Site 1, cameras are deployed at pre-determined GPS points on a 500-m grid, and at Site 2, cameras are strategically deployed with a bias towards forest and forest margin habitat where possible. A portion of cameras are also deployed in open farmland habitat and mixed scrub. We then use the abundance-induced heterogeneity Royle–Nichols model to estimate mean animal abundance and detection probabilities for cameras in each habitat type. Model selection suggests that only cat abundance varies by habitat type. Mean cat abundance is highest at forest margin cameras for both deployment methods (3 cats [95% CI 1.9–4.5] Site 1, and 1.7 cats [95% CI 1.2–2.4] Site 2) but not substantially higher than in forest habitats (1.7 cats [95% CI 0.8–3.6] Site 1, and 1.5 cats [95% CI 1.1–2.0] Site 2). Model selection shows detection probabilities do not vary substantially by habitat (although they are also higher for cameras in forest margins and forest habitats) and are similar between sites (8.6% [95% CI 5.4–13.4] Site 1, and 8.3% [5.8–11.9] Site 2). Cat detections by camera traps are higher when placed in forests and forest margins; thus, strategic placement may be preferable when monitoring feral cats in a pastoral landscape.

Humans, but not their dogs, displace pumas from their kills: An experimental approach

Domestic dogs are the most abundant large carnivore on the planet, and their ubiquity has led to concern regarding the impacts of dogs as predators of and competitors with native wildlife. If native large carnivores perceive dogs as threatening, impacts could extend to the community level by altering interactions between large carnivores and their prey. Dog impacts may be further exacerbated if these human-associated predators are also perceived as indicators of risk from humans. However, observational approaches used to date have led to ambiguity regarding the effects of dog presence on wildlife. We experimentally quantified dog impacts on the behavior of a native large carnivore, presenting playbacks of dog vocalizations to pumas in central California. We show that the perceived presence of dogs has minimal impacts on puma behavior at their kill sites, and is no more likely to affect total feeding time at kills than non-threatening controls. We previously demonstrated that pumas exhibit strong responses to human cues, and here show that perceived risk from human presence far exceeds that from dogs. Our results suggest that protected areas management policies that restrict dogs but permit human access may in some cases be of limited value for large carnivores.

Modeling habituation of introduced predators to unrewarding bird odors for conservation of ground-nesting shorebirds

Foraging mammalian predators face a myriad of odors from potential prey. To be efficient, they must focus on rewarding odors while ignoring consistently unrewarding ones. This may be exploited as a nonlethal conservation tool if predators can be deceived into ignoring odors of vulnerable secondary prey. To explore critical design components and assess the potential gains to prey survival of this technique, we created an individual-based model that simulated the hunting behavior of three introduced mammalian predators on one of their secondary prey (a migratory shorebird) in the South Island of New Zealand. Within this model, we heuristically assessed the outcome of habituating the predators to human-deployed unrewarding bird odors before the bird's arrival at their breeding grounds, i.e., the predators were "primed." Using known home range sizes and probabilities of predators interacting with food lures, our model suggests that wide-ranging predators should encounter a relatively large number of odor points (between 10 and 115) during 27 d of priming when odor is deployed within high-resolution grids (100-150 m). Using this information, we then modeled the effect of different habituation curves (exponential and sigmoidal) on the probability of predators depredating shorebird nests. Our results show that important gains in nest survival can be achieved regardless of the shape of the habituation curve, but particularly if predators are fast olfactory learners (exponential curve), and even if some level of dishabituation occurs after prey become available. Predictions from our model can inform the amount and pattern in which olfactory stimuli need to be deployed in the field to optimize encounters by predators, and the relative gains that can be expected from reduced predation pressure on secondary prey under different scenarios of predator learning. Habituating predators to odors of threatened secondary prey may have particular efficacy as a conservation tool in areas where lethal predator control is not possible or ethical, or where even low predator densities can be detrimental to prey survival. Our approach is also relevant for determining interaction probabilities for devices other than odor points, such as bait stations and camera traps.