Discrimination of introduced predators by ontogenetically naïve prey scales with duration of shared evolutionary history

Housework or vigilance? Bilbies alter their burrowing activity under threat of predation by feral cats

Behavioral adjustments to predation risk not only impose costs on prey species themselves but can also have cascading impacts on whole ecosystems. The greater bilby (Macrotis lagotis) is an important ecosystem engineer, modifying the physical environment through their digging activity, and supporting a diverse range of sympatric species that use its burrows for refuge and food resources. The bilby has experienced a severe decline over the last 200 years, and the species is now restricted to ~20% of its former distribution. Introduced predators, such as the feral cat (Felis catus), have contributed to this decline. We used camera traps to monitor bilby burrows at four sites in Western Australia, where bilbies were exposed to varying levels of cat predation threat. We investigated the impact of feral cats on bilby behavior at burrows, particularly during highly vulnerable periods when they dig and clear away soil or debris from the burrow entrance as they perform burrow maintenance. There was little evidence that bilbies avoided burrows that were visited by a feral cat; however, bilbies reduced the time spent performing burrow maintenance in the days following a cat visit (P = 0.010). We found the risk posed to bilbies varied over time, with twice the cat activity around full moon compared with dark nights. Given bilby burrows are an important resource in Australian ecosystems, predation by feral cats and the indirect impact of cats on bilby behavior may have substantial ecosystem function implications.

Identifying the most effective behavioural assays and predator cues for quantifying anti-predator responses in mammals: a systematic review

BACKGROUND

Mammals, globally, are facing population declines. Protecting and breeding threatened populations inside predator-free havens and translocating them back to the wild is commonly viewed as a solution. These approaches can expose predator-naïve animals to predators they have never encountered and as a result, many conservation projects have failed due to the predation of individuals that lacked appropriate anti-predator responses. Hence, robust ways to measure anti-predator responses are urgently needed to help identify naïve populations at risk, to select appropriate animals for translocation, and to monitor managed populations for changes in anti-predator traits. Here, we undertake a systematic review that collates existing behavioural assays of anti-predator responses and identifies assay types and predator cues that provoke the greatest behavioural responses.

METHODS

We retrieved articles from academic bibliographic databases and grey literature sources (such as government and conservation management reports), using a Boolean search string. Each article was screened against eligibility criteria determined using the PICO (Population-Intervention-Comparator-Outcome) framework. Using data extracted from each article, we mapped all known behavioural assays for quantifying anti-predator responses in mammals and examined the context in which each assay has been implemented (e.g., species tested, predator cue characteristics). Finally, with mixed effects modelling, we determined which of these assays and predator cue types elicit the greatest behavioural responses based on standardised difference in response between treatment and control groups.

REVIEW FINDINGS

We reviewed 5168 articles, 211 of which were eligible, constituting 1016 studies on 126 mammal species, a quarter of which are threatened by invasive species. We identified six major types of behavioural assays: behavioural focals, capture probability, feeding station, flight initiation distance, giving-up density, and stimulus presentations. Across studies, there were five primary behaviours measured: activity, escape, exploration, foraging, and vigilance. These behaviours yielded similar effect sizes across studies. With regard to study design, however, studies that used natural olfactory cues tended to report larger effect sizes than those that used artificial cues. Effect sizes were larger in studies that analysed sexes individually, rather than combining males and females. Studies that used 'blank' control treatments (the absence of a stimulus) rather than a treatment with a control stimulus had higher effect sizes. Although many studies involved repeat measures of known individuals, only 15.4% of these used their data to calculate measures of individual repeatability.

CONCLUSIONS

Our review highlights important aspects of experimental design and reporting that should be considered. Where possible, studies of anti-predator behaviour should use appropriate control treatments, analyse males and females separately, and choose organic predator cues. Studies should also look to report the individual repeatability of behavioural traits, and to correctly identify measures of uncertainty (error bars). The review highlights robust methodology, reveals promising techniques on which to focus future assay development, and collates relevant information for conservation managers.

Can native predators be used as a stepping stone to reduce prey naivety to novel predators?

Predator naivety negatively affects reintroduction success, and this threat is exacerbated when prey encounters predators with which they have had no evolutionary experience. While methods have been developed to inculcate fear into such predator-naïve individuals, none have been uniformly successful. Exposing ontogenetically- and evolutionary-naïve individuals first to native predators may be an effective stepping stone to improved responses to evolutionarily novel predators. We focused on greater bilbies (Macrotis lagotis) and capitalized on a multi-year mammalian recovery experiment whereby western quolls (Dasyurus geoffroii) were reintroduced into parts of a large fenced reserve that contained a population of naïve bilbies. We quantified a suite of anti-predator behaviors and measures of general wariness across quoll-exposed and quoll-naive bilby populations. We then translocated both quoll-exposed and quoll-naïve individuals into a large enclosure that contained feral cats (Felis catus) and monitored several behaviors. We found that bilbies can respond appropriately to quolls but found only limited support that experience with quolls better-prepared bilbies to respond to cats. Both populations of bilbies rapidly modified their behavior in a similar manner after their reintroduction to a novel environment. These results may have emerged due to insufficient prior exposure to quolls, inappropriate behavioral tests, or insufficient predation risk during cat exposure. Alternatively, quolls and cats are only distantly related and may not share sufficient similarities in their predatory cues or behavior to support such a learning transfer. Testing this stepping stone hypothesis with more closely related predator species and under higher predation risk would be informative.

When ancestry haunts – can evolutionary links to ancestors affect vulnerability of Australian prey to introduced predators? A preliminary study

The high extinction risk of Australian marsupials has been attributed to their failure to recognise novel predators, the application of inappropriate antipredator responses, and advanced hunting strategies of novel predators. This study is a preliminary attempt to explore whether the Lumholtz’ tree-kangaroo (Dendrolagus lumholtzi) (a) is able to recognise odour cues from different predators as threats, and (b) possesses predator-archetype specific antipredator responses. A small number of available captive tree-kangaroos were exposed to faecal odours from two extant predators of different archetypes (python, dingo), a regionally extinct predator which closely matches past terrestrial predators (Tasmanian devil), and a novel predator (domestic dog). Lavender oil was used as non-predator novel odour and water as control. Results suggest that all subjects associated the presented odours with a threat, albeit to different degrees, but did not display predator-archetype specific responses. It appears that this species applies an ancestral antipredator response of flight-on-the ground when encountering predators, including novel predators. Although the results need to be confirmed with more animals, further studies on the vulnerability of Australian prey to novel predators should take the ancestral history of Australian prey species into account.

Sniffing out danger: rapid antipredator training of an endangered marsupial

Globally, predator aversion training has assisted naive prey species to learn to evade introduced predators, improving translocation success. Eastern barred bandicoots (Perameles gunnii; hereafter ‘bandicoot’) are extinct on mainland Australia due to habitat loss and introduced predators, and are the focus of a long-term captive breeding and reintroduction program. Our trials showed that captive bandicoots failed to recognise cat (Felis catus) scents as belonging to a predator, suggesting prey naivety towards cats. We trialled five stimuli to elicit short-term fear behaviour in bandicoots. An automatic compressed air spray and automatic bin lid were most effective. We coupled these stimuli with cat urine during predator aversion training and presented them to bandicoots on three occasions. Bandicoots learnt to avoid the area containing cat urine, suggesting bandicoots are capable of learning new behaviours rapidly. Six trained and five untrained captive bandicoots where released onto Summerland Peninsular, Phillip Island (with cat densities at 1.1 cats/km2). Both had high survival and recapture rates 7 months after release. Training endangered species to avoid introduced predators could assist with long-term species recovery.

Loss of Predator Discrimination by Critically Endangered Vancouver Island Marmots Within Five Generations of Breeding for Release

Conservation translocations, which involve the intentional movement and release of organisms for conservation benefit, are increasingly required to recover species of conservation concern. In order to maximize post-release survival, and to accomplish conservation translocation objectives, animals must exhibit behaviors that facilitate survival in the wild. The Vancouver Island marmot (Marmota vancouverensis) is a critically endangered endemic in Canada which has been captive-bred for 24 years for reintroductions and reinforcements that have increased the wild population from ~30 to more than 200 individuals. Despite this success many marmots are killed by predators after release and predation represents a major hurdle to full marmot recovery. To better understand if captive-bred marmots are prepared for the novel environment into which they will be released, and to determine whether such suitability changes over time, we presented taxidermy mounts of mammalian predators and non-predators to marmots that were wild-caught, and captive born for between one and five generations. We also examined mortality of offspring from marmots we tested that had been released to the wild. A minimum of 43% of offspring were killed by predators in the wild over 17 years, most by cougars. Marmots in captivity generally responded to taxidermy mounts by decreasing foraging and increasing vigilance, and overall responded more strongly to predators than non-predators, especially wolves. However, marmots in captivity for more than two generations lacked discrimination between cougars, non-predators, and controls, suggesting a rapid loss of predator recognition. This study was only possible because predator-recognition trials were initiated early in the conservation translocation program, and could then be repeated after a number of generations. The finding that changes occurred relatively rapidly (within five generations during which changes in genetic diversity were negligible) suggests that behavioral suitability may deteriorate more rapidly than genetics would suggest. Strategies addressing potential behavior loss should be considered, including sourcing additional wild individuals or pre-release training of captive-born individuals. Subsequently, post-release survival should be monitored to determine the efficacy of behavior-optimization strategies.

Canids potentially threaten bilbies at Astrebla Downs National Park

The ecological role of canids in arid Australia is unresolved. Some argue they play a role regulating populations of herbivores and introduced mesopredators such as feral cats (Felis catus) and foxes (Vulpes vulpes). However, evidence also suggests they pose a threat to native species populations. The aims of this study were to determine the extent of canid predation on the bilby population at Astrebla Downs National Park, Queensland, to improve our understanding of the ecological role that canids serve in the park and to determine whether seasonal changes in the canid diet can be used to predict if and when management should intervene. Canid scats (n=723) were collected over seven years and their content examined. The percentage of bilby remains in the canid scats varied from 13 to 85% (mean=43%) and was 20–100% by volume. In total, 23 vertebrate species were identified in canid scats. The percentage of cat remains was 0–44% (mean=11%), peaking in 2013 during a cat plague and coinciding with canids actively hunting cats. Fox remains were not detected in dog scats. These results indicate that canids had a varied diet and at times threatened the bilby population at Astrebla.

Are British urban foxes (Vulpes vulpes) "bold"? The importance of understanding human-wildlife interactions in urban areas

Human-wildlife interactions are believed to be increasing in urban areas. In Britain, numerous media reports have stated that urban foxes (Vulpes vulpes) are becoming "bolder," thereby posing a risk to public safety. However, such claims overlook how an individual's personality might influence urban fox behavior. Personality determines multiple aspects of an animal's interactions with both conspecifics and its environment, and can have a significant impact on how people perceive wildlife. Furthermore, describing urban foxes as "bold" confounds two different but inter-related behaviors, both of which influence an animal's propensity to take risks. Neophobia affects an animal's reaction to novelty, wariness its reaction to potential threats. Since urban wildlife frequently encounters both novel and threatening stimuli, a highly adaptable species such as the red fox might be predicted to exhibit reduced neophobia and wariness. We investigated how social status influenced both behaviors in Bristol's fox population. Dominant foxes were significantly more neophobic and warier than subordinates, which adopt a more exploratory and risk-taking lifestyle to meet their energetic and other needs. We found no seasonal effect on neophobia and wariness, although this may be due to sample size. The presence of conspecifics decreased neophobia for dominants, and wariness for both dominants and subordinates. We highlight the importance of considering animal social status and personality when planning management protocols, since interventions that destabilize fox social groups are likely to increase the number of subordinate foxes in the population, thereby increasing rather than decreasing the number of interactions between humans and urban foxes.

Predator avoidance behavior of nocturnal and diurnal rodents

Animals trade-off predation risk against feeding opportunities and prey species may use signals or cues of predators to assess predation risk. We analyzed the mesopredators pine and stone marten (Martes martes, M. foina) and nocturnal and diurnal rodents (Glis glis, Apodemus spp., Sciurus vulgaris). The non-experimental approach used camera traps at feeders which were visited by both, predator and prey. As prey species can eavesdrop on predator signals/cues, there should show some avoidance behavior. The study was conducted on a small mountain in Germany, largely covered by wood, between 29.6.2018 and 5.10.2018. Camera traps were placed 0.6 m near a feeder. Food was replenished regularly to provide a continuous food supply. 34 camera traps provided data for an analysis; total trap nights were 513 (12,312 h). Martens detected the food sources first in 10 instances, and prey species Apodemus/G. glis in 24 instances. G. glis seemed to generally avoid places where martens were feeding while Apodemus and Sciurus did not. The visitations of G. glis depended on whether martens were the first visitors and it significantly avoided such places. Similarly, Apodemus appeared less often at a feeder when martens have been present as a first visitor. The time interval to resume feeding to a monitored feeder after a marten visit was significantly longer compared to a control in G. glis, but not in Apodemus and S. vulgaris. The study shows different responses, with the weakest in the diurnal rodent, and the highest in G. glis. Thus, if a food resource was known by prey species before a predator occurred, the trade-off was shifted towards feeding, but when the predators detect the food source first, the trade-off was shifted to predator avoidance.

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.

Relaxed predation theory: size, sex and brains matter

Australia's wildlife is being considerably impacted by introduced mammalian predators such as cats (Felis catus), dogs (Canis lupus familiaris), and foxes (Vulpes vulpes). This is often attributed to native wildlife being naïve to these introduced predators. A systematic review of the literature reveals that native metatherians (body mass range 0.02-25 kg) do not recognise, and show relaxed antipredator behaviours towards, native and some introduced mammalian predators. Native eutherians (all with body mass < 2 kg), however, do appear to recognise and exhibit antipredator behaviours towards both native and introduced predators. Based on our findings, we propose a novel theory, the 'Relaxed Predation Theory'. Our new theory is based on the absence of large mammalian predators leading to reduced predation pressure in Australia during the past 40000-50000 years, and on three key differences between Australian metatherians and eutherians: size, sex, and brains. In light of this Relaxed Predation Theory, we make a number of recommendations for the conservation of Australian wildlife: (i) predator avoidance training of suitable species; (ii) exclusion fencing to exclude some, but not all, predators to facilitate the development of antipredator behaviours; (iii) captive breeding programs to prevent the extinction of some species; and (iv) reintroduction of Australia's larger predators, potentially to compete with and displace introduced predators. A more detailed understanding of the responses of Australian mammals to predators will hopefully contribute to the improved conservation of susceptible species.

A comparative study of survival, recruitment and population growth in two translocated populations of the threatened greater bilby (Macrotis lagotis)

Abstract Context Translocations have been widely used to re-establish populations of threatened Australian mammalian species. However, they are limited by the availability of sites where key threats can be effectively minimised or eliminated. Outside of ‘safe havens’, threats such as exotic predators, introduced herbivores and habitat degradation are often unable to be completely eliminated. Understanding how different threats affect Australian mammal populations can assist in prioritising threat-management actions outside of safe havens. AimsWe sought to determine whether translocations of the greater bilby to two sites in the temperate zone of South Australia could be successful when human-induced threats, such as prior habitat clearance, historic grazing, the presence of feral cats and European rabbits, could not be completely eliminated. Methods Greater bilbies were regularly cage trapped at two translocation sites and a capture–mark–recapture study was used to determine survival, recruitment and population growth at both sites. Key results Our study showed that bilbies were successfully translocated to an offshore island with a previous history of grazing and habitat clearance, but which was free of exotic predators. At a second site, a mainland exclosure with feral cats and European rabbits present, the bilby population declined over time. Adult bilbies had similar survival rates in both populations; however, the mainland bilby population had low recruitment rates and low numbers of subadults despite high adult female fecundity. ConclusionsThe results indicated that past grazing and habitat clearance did not prevent the bilby population on the offshore island establishing and reaching a high population density. In the mainland exclosure, the low recruitment is probably due to feral cats predating on subadult bilbies following pouch emergence. Implications The results demonstrated that the bilby, an ecologically flexible Australian marsupial, can be successfully translocated to sites with a history of habitat degradation if exotic predators are absent. At the mainland exclosure site, threat mitigation for bilbies should focus on control or eradication of the feral cats. The control of European rabbits without control of feral cats could lead to prey-switching by feral cats, further increasing predation pressure on the small bilby population.

In situ predator conditioning of naive prey prior to reintroduction

Many translocations and introductions to recover threatened populations fail because predators kill prey soon after release; a problem exacerbated for predator-naive prey. While pre-release training has been shown to work in some situations, it is time consuming and relies on using inferred predator cues and treating small groups. We review a relatively new and very promising management tool: in situ, pre-release predator conditioning. Here, the goal is to allow prey in large enclosures to live with low densities of predators to accelerate selection for antipredator traits (in an evolutionary sense) or provide prey essential experience with predators that they will later encounter. We review the published results of a large-scale, controlled experiment where we have permitted burrowing bettongs (Bettongia lesueur) and greater bilblies (Macrotis lagotis) to live with low densities of feral cats (Felis catus), a species implicated in their widespread decline and localized extinction. We found that both species could persist with cats, suggesting that future work should define coexistence thresholds-which will require knowledge of prey behaviour as well as the structure of the ecological community. Compared to control populations, predator-naive prey exposed to cats has a suite of morphological and behavioural responses that seemingly have increased their antipredator abilities. Results suggest that predator-conditioned bilbies survive better when released into a large enclosure with an established cat population; future work will determine whether this increased survival extends to the wild. This article is part of the theme issue 'Linking behaviour to dynamics of populations and communities: application of novel approaches in behavioural ecology to conservation'.

Overcoming prey naiveté: Free-living marsupials develop recognition and effective behavioral responses to alien predators in Australia

Naiveté in prey arises from novel ecological mismatches in cue recognition systems and antipredator responses following the arrival of alien predators. The multilevel naiveté framework suggests that animals can progress through levels of naiveté toward predator awareness. Alternatively, native prey may be preadapted to recognize novel predators via common constituents in predator odors or familiar predator archetypes. We tested predictions of these competing hypotheses on the mechanisms driving behavioral responses of native species to alien predators by measuring responses of native free-living northern brown bandicoots (Isoodon macrourus) to alien red fox (Vulpes vulpes) odor. We compared multiple bandicoot populations either sympatric or allopatric with foxes. Bandicoots sympatric with foxes showed recognition and appropriate antipredator behavior toward fox odor via avoidance. On the few occasions bandicoots did visit, their vigilance significantly increased, and their foraging decreased. In contrast, bandicoots allopatric with foxes showed no recognition of this predator cue. Our results suggest that vulnerable Australian mammals were likely naïve to foxes when they first arrived, which explains why so many native mammals declined soon after fox arrival. Our results also suggest such naiveté can be overcome within a relatively short time frame, driven by experience with predators, thus supporting the multilevel naiveté framework.