Behavioural correlations across multiple stages of the antipredator response: do animals that escape sooner hide longer?

Effects of Varied Stimuli on Escape Behavior Diversification of Himalayan Marmots for Different Human Disturbances

We measured the alert distance (AD), flight-initiation distance (FID), buffer distance (BD), and distance fled (DF) of Himalayan marmots (Marmota himalayana) from four populations experiencing human disturbances of the same persistence but different intensities when subjected to varied stimuli (a running or walking man with or without a leashed dog and a dog alone). We analyzed the effects of different stimuli on the AD, FID, BD, and DF of marmots from each population and the relationship among the AD, FID, and DF to illustrate the escape strategy diversification of the studied marmots for different human disturbances when disturbed by varied stimuli. We found that intra-population diversification emerged when the marmots were threatened by different stimuli. The AD and FID were shorter when an individual was walking toward than when he was running toward the focal marmots. A man with a leashed dog as a stimulus produced a similar result to that of a man alone. Nevertheless, no diversification emerged when a single dog was the threat, and all three distances triggered due to the dog were significantly shorter than those triggered due to a man alone (walking or running) or a man with a leashed dog approaching the marmots. Inter-population diversification also emerged when the marmots from the four populations were disturbed by the same stimulus: when threatened by an individual or a man with a leashed dog, their escape behavior was determined by the intensity of the disturbance. The changes in the AD and FID were similar across all four populations, with the two distances increasing with the decrease in disturbance intensity, but the DF showed no significant variation across all the four areas. No significant inter-population diversification emerged when the marmots were threatened by a single dog. These diversifications may result from the different levels of habituation of marmots to human disturbances and the different sizes and, consequently, visibilities of humans and dogs.

More complex anti-predator behaviors develop with age in Chinese water deer fawns

An anti-predator strategy increases the fitness of the prey itself, in which vigilance behavior plays an important role. Numerous studies have explored the correlation between prey age and the level of vigilance towards an approaching predator. However, limited studies have delved into the development of vigilant behaviors, much less the vigilant decision-chains. Chinese water deer (Hydropotes inermis), an extremely timid and sensitive animal capable of independent movement at birth, exhibits changes in vigilance strategy from newborn to the end of suckling period. Through individual recognition and standardized flight initiation trial, we measured the distances between the approaching predator and the occurrence of various vigilance behaviors (stare, flight, roaring, stretching neck, vigilant stomping). Our results reveal that Chinese water deer exhibited the vigilant strategy of roaring in the early stage (<3 weeks), and stretching neck and vigilant stomping in the late stage (≥10 weeks), displaying an overall trend of increasing complexity. The vigilant decision-chains of the fawns become more diverse with age. Fawns prioritize their own intrinsic status when making flight decisions under the same threat, with age, birth weight, and pre-flight behaviors emerging as the dominant determinants. Overall, our findings indicate that suckling fawns of Chinese water deer adopt different vigilance behavioral strategies with their development and depending on their age, birth weight and pre-flight behaviors when faced with a threat.

Human presence shifts the landscape of fear for a free-living mammal

Humans may play a key role in providing small prey mammals spatial and temporal refuge from predators, but few studies have captured the heterogeneity of these effects across space and time. Global COVID-19 lockdown restrictions offered a unique opportunity to investigate how a sudden change in human presence in a semi-urban park impacted wildlife. Here, we quantify how changes in the spatial distributions of humans and natural predators influenced the landscape of fear for the California ground squirrel (Otospermophilus beecheyi) in a COVID-19 pandemic (2020) and non-COVID (2019) year. We used a structural equation modeling approach to explore the direct and indirect effects of human presence, predator presence, and habitat features on foraging that reflected fear responses (e.g., giving-up densities [GUDs], number of foragers, and average food intake rate while at food patches). In 2019, humans and dogs had moderate effects on GUDs; squirrels were less fearful (lower GUDs) in areas frequently visited by humans and dogs, but the effects of raptors were weak. In contrast, in 2020, the effects of humans and dogs on GUDs were weak; squirrels were more fearful of high raptor activity, open sky, and ground cover. In both years, squirrels farthest from refuge were the most risk-averse. Overall, our analyses revealed an increase in perceived risk from natural predators in 2020 associated with a change in the concentration of human presence. Thus, risk-sensitive foraging was dynamic across space and time, depending on a complex interplay among human and dog activity, natural predators, and microhabitat features. Our findings elucidate the myriad ways humans directly and indirectly influence animal perception of safety and danger.

Vole hunting: novel predatory and carnivorous behavior by California ground squirrels

Dietary flexibility allows animals to respond adaptively to food pulses in the environment. Here we document the novel emergence of widespread hunting of California voles and carnivorous feeding behavior by California ground squirrels. Over two months in the twelfth year of a long-term study on the squirrel population, we document 74 events of juvenile and adult ground squirrels of both sexes depredating, consuming, and/or competing over vole prey. Our video footage, photographic evidence, and direct observations of marked individual squirrels provide insights into the ecological circumstances favoring behavioral flexibility in foraging associated with a decadal peak in vole abundance. Digital video images related to the article are available at http://www.momo-p.com/showdetail-e.php?movieid=momo241126ob01a.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10164-024-00832-6.

Lifting the Veil of Darkness: Thermal Technology Facilitates Collection of Flight-Initiation Distances by Night

Flight-Initiation Distance (FID)-a direct measure of an individual animal's escape response-is a widely used method to study escape ecology in fauna. The technique has primarily been applied to bird species that are active by day. Indexing the escape behaviour of nocturnal species has been limited due to the need for light to detect and observe animals which confounds behavioural responses. We demonstrate the use of existing high-end thermal technology to facilitate standardised, un-biased, nocturnal FIDs in small and large, terrestrial and arboreal animals, which feature initial separation (starting) distances which are the same by day and night. We provide the following (1) method for collecting FIDs by night which specifically addresses solutions to novel challenges associated with collecting these by night, (2) report of the FIDs of some strictly nocturnal bird and mammal species and compare diurnal and nocturnal FIDs for some species, (3) demonstration that the positive daytime relationship between FID and Starting Distance also occurs by night, and (4) minimum sample size threshold for quantifying escape responses and how these vary when sampling the FIDs of different animal species by night. We demonstrate the capacity to conduct nocturnal FIDs on a broad range of taxa not previously studied. We recommend 25-50 samples are needed to accurately quantify a species escape response in a particular context. Our method expands the capacity to understand how species escape by night, a critical period during which many predator-prey interactions occur.

Do human-wildlife interactions predict offspring hiding strategies in peri-urban fallow deer?

Human activities can induce significant behavioural changes in wildlife. Often explored through extractive interactions (e.g. hunting) that can favour certain behavioural traits, the implications of non-extractive ones, such as wildlife feeding, remain understudied. Research shows that people tend to favour bolder individuals within populations despite their dynamics and consequences being unclear. Using fallow deer in a peri-urban environment, we studied whether mothers that show reduced fear of humans and consistently approach them for food adopt weaker anti-predator strategies by selecting less concealed fawning bedsites closer to human hotspots. This would provide the advantage of additional feeding opportunities in comparison with shyer mothers while keeping their fawns close. Our dataset encompassed 281 capture events of 172 fawns from 110 mothers across 4 years. Surprisingly, mothers that regularly accepted food from humans selected more concealed bedsites farther from human hotspots, giving their offspring better protection while also benefitting from additional food during lactation. Our results show behavioural adaptations by a subset of females and, for the first time, link the tendency to approach humans and strategies to protect offspring. Given previous findings that these begging females also deliver heavier fawns at birth, our research further investigates human-wildlife feeding interactions and their behavioural implications.

Sex- and state-dependent covariation of risk-averse and escape behavior in a widespread lizard

Mounting evidence has shown that personality and behavioral syndromes have a substantial influence on interspecific interactions and individual fitness. However, the stability of covariation among multiple behavioral traits involved in antipredator responses has seldom been tested. Here, we investigate whether sex, gravidity, and parasite infestations influence the covariation between risk aversion (hiding time within a refuge) and escape response (immobility, escape distance) using a viviparous lizard, Zootoca vivipara, as a model system. Our results demonstrated a correlation between risk-averse and escape behavior at the among-individual level, but only in gravid females. We found no significant correlations in either males or neonates. A striking result was the loss of association in postparturition females. This suggests that the "risk-averse - escape" syndrome is ephemeral and only emerges in response to constraints on locomotion driven by reproductive burden. Moreover, parasites have the potential to dissociate the correlations between risk aversion and escape response in gravid females, yet the causal chain requires further examination. Overall, our findings provide evidence of differences in the association between behaviors within the lifetime of an individual and indicate that individual states, sex, and life stages can together influence the stability of behavioral syndromes.

Sensory integration of danger and safety cues may explain the fear of a quiet coyote

Sensory integration theory predicts natural selection should favour adaptive responses of animals to multiple forms of information, yet empirical tests of this prediction are rare, particularly in free-living mammals. Studying indirect predator cues offers a salient opportunity to inquire about multimodal risk assessment and its potentially interactive effects on prey responses. Here we exposed California ground squirrels from two study sites (that differ in human and domestic dog activity) to acoustic and/or olfactory predator cues to reveal divergent patterns of signal dominance. Olfactory information most strongly predicted space use within the testing arena. That is, individuals, especially those at the human-impacted site, avoided coyote urine, a danger cue that may communicate the proximity of a coyote. By contrast, subjects allocated less time to risk-sensitive behaviours when exposed to acoustic cues. Specifically, although individuals were consistent in their behavioural responses across trials, 'quiet coyotes' (urine without calls) significantly increased the behavioural reactivity of prey, likely because coyotes rarely vocalize when hunting. More broadly, our findings highlight the need to consider the evolution of integrated fear responses and contribute to an emerging understanding of how animals integrate multiple forms of information to trade off between danger and safety cues in a changing world.

Integrating sensory ecology and predator-prey theory to understand animal responses to fire

Fire regimes are changing dramatically worldwide due to climate change, habitat conversion, and the suppression of Indigenous landscape management. Although there has been extensive work on plant responses to fire, including their adaptations to withstand fire and long-term effects of fire on plant communities, less is known about animal responses to fire. Ecologists lack a conceptual framework for understanding behavioural responses to fire, which can hinder wildlife conservation and management. Here, we integrate cue-response sensory ecology and predator-prey theory to predict and explain variation in if, when and how animals react to approaching fire. Inspired by the literature on prey responses to predation risk, this framework considers both fire-naïve and fire-adapted animals and follows three key steps: vigilance, cue detection and response. We draw from theory on vigilance tradeoffs, signal detection, speed-accuracy tradeoffs, fear generalization, neophobia and adaptive dispersal. We discuss how evolutionary history with fire, but also other selective pressures, such as predation risk, should influence animal behavioural responses to fire. We conclude by providing guidance for empiricists and outlining potential conservation applications.

Fear generalization and behavioral responses to multiple dangers

Animals often exhibit consistent-individual differences (CIDs) in boldness/fearfulness, typically studied in the context of predation risk. We focus here on fear generalization, where fear of one danger (e.g., predators) is correlated with fear of other dangers (e.g., humans, pathogens, moving vehicles, or fire). We discuss why fear generalization should be ecologically important, and why we expect fear to correlate across disparate dangers. CIDs in fear are well studied for some dangers in some taxa (e.g., human fear of pathogens), but not well studied for most dangers. Fear of some dangers has been found to correlate with general fearfulness, but some cases where we might expect correlated fears (e.g., between fear of humans, familiar predators, and exotic predators) are surprisingly understudied.

Beyond simple habituation: Anthropogenic habitats influence the escape behaviour of spur-winged lapwings in response to both human and non-human threats

Habitat development may affect wildlife behaviour, favouring individuals or behaviours that cope better with perceived threats (predators). Bolder behaviours in human-dominated habitats (HDH; e.g. urban and rural settlements) may represent habituation specifically to humans, or a general reduction in predator-avoidance response. However, such carry-over effects across threat types (i.e. beyond humans) and phases of the escape sequence have not been well studied to date. Here we investigated escape behaviours of a locally common wader species, the spur-winged lapwing Vanellus spinosus. We assayed their flight initiation distance (FID) and subsequent escape behaviours in agricultural areas and in HDH. We found that lapwings in HDH were bolder, and that the difference was manifested in several phases of the predator-avoidance sequence (shorter FIDs, shorter distances fled, and a higher probability of escape by running vs. flying). When re-approached (by an observer) after landing, lapwings in HDH were also more repetitive in their FID than those in other habitats. To determine whether this apparent bolder behaviour in HDH areas is merely a consequence of habituation to humans or represents a broader behavioural change, we introduced an additional threat type-a remotely-operated taxidermic jackal ('Jack-Truck'). Finding bolder responses in the HDH to the human threat alone (and not to the Jack-Truck) could have supported the habituation hypothesis. In contrast, however, we found a bolder response in the HDH to both threat types, as well as a correlation between their FIDs across different sites. These bolder behaviours suggest that HDH impose a broader behavioural change on lapwings, rather than just simple habituation. Overall, our findings demonstrate how FID trials can reveal strong behavioural carry-over effects of HDH following human and non-human threats, including effects on the subsequent phases of escaping the predator. Further, FID assays may reveal consistent behavioural types when assessed under field conditions, and offer a direct way to differentiate among the various poorly understood and non-mutually exclusive mechanisms that lead to behavioural differences among organisms in HDH. The mechanistic perspective is essential for understanding how rapid urbanization impacts wildlife behaviour, populations, and the range of behaviours within them, even in species apparently resilient to such environmental changes.

Exposure to polystyrene nanoplastics induces an anxiolytic-like effect, changes in antipredator defensive response, and DNA damage in Swiss mice

Although the in vivo toxicity of nanoplastics (NPs) has already been reported in different model systems, their effects on mammalian behavior are poorly understood. Thus, we aimed to evaluate whether exposure to polystyrene (PS) NPs (diameter: 23.03 ± 0.266 nm) alters the behavior (locomotor, anxiety-like and antipredator) of male Swiss mice, induces brain antioxidant activity, and erythrocyte DNA damage. For this, the animals were exposed to NPs for 20 days at different doses (6.5 ng/kg and 6500 ng/kg). Initially, we did not observe any effect of pollutants on the locomotor activity of the animals (inferred via open field test and Basso mouse scale for locomotion). However, we noticed an anxiolytic-like behavior (in the open field test) and alterations in the antipredatory defensive response of mice exposed to PS NPs, when confronted with their predator potential (snake, Pantherophis guttatus). Furthermore, such changes were associated with suppressing brain antioxidant activity, inferred by lower DPPH radical scavenging activity, reduced total glutathione content, as well as the translocation and accumulation of NPs in the brain of the animals. In addition, we noted that the treatments induced DNA damage, evaluated via a single-cell gel electrophoresis assay (comet assay) applied to circulating erythrocytes of the animals. However, we did not observe a dose-response effect for all biomarkers evaluated and the estimated accumulation of PS NPs in the brain. The values of the integrated biomarker response index and the results of the principal component analysis (PCA) and the hierarchical clustering analysis confirmed the similarity between the responses of animals exposed to different doses of PS NPs. Therefore, our study sheds light on how PS NPs can impact mammals and reinforce the ecotoxicological risk associated with the dispersion of these pollutants in natural environments and their uptake by mammals.

Social context mediates the expression of a personality trait in a gregarious lizard

The social environment is a key factor that influences behavioural traits across a wide array of species. Yet, when investigating individual differences in behaviour, studies tend to measure animals in isolation from other conspecifics-even in social species. Surprisingly, whether behavioural traits measured in isolation are predictive of individual-level behaviour when in social groups is still poorly understood. Here, we repeatedly measured risk-taking behaviour (i.e. boldness; 741 total trials) in both the presence and absence of conspecifics in a social lizard, the delicate skink (Lampropholis delicata). Further, we manipulated food availability during group trials to test whether the effect of the social environment on risk-taking behaviour was mediated by competition over resources. Using 105 lizards collected from three independent populations, we found that individual risk-taking behaviour was repeatable when measured in either social isolation or within groups both with and without food resources available. However, lizards that were bolder during individual trials were not also bolder when in groups, regardless of resource availability. This was largely driven by individual differences in social behavioural plasticity, whereby individual skinks responded differently to the presence of conspecifics. Together, this resulted in a rank order change of individual behavioural types across the social conditions. Our results highlight the importance of the social environment in mediating animal personality traits across varying levels of resource availability. Further, these findings suggest that behavioural traits when measured in isolation, may not reflect individual variation in behaviour when measured in more ecologically realistic social groups.

Intolerant baboons avoid observer proximity, creating biased inter-individual association patterns

Social network analysis is an increasingly popular tool for behavioural ecologists exploring the social organisation of animal populations. Such analyses require data on inter-individual association patterns, which in wild populations are often collected using direct observations of habituated animals. This assumes observers have no influence on animal behaviour; however, our previous work showed that individuals in a habituated group of chacma baboons (Papio ursinus griseipes) displayed consistent and individually distinct responses to observer approaches. We explored the implications of our previous findings by measuring the inter-individual association patterns of the same group of chacma baboons at different observer distances. We found a strong positive association between individual tolerance levels (towards observers) and how often an animal appeared as a neighbour to focal animals when observers were nearer, and a neutral relationship between the same variables when the observer was further away. Additionally, association matrices constructed from different observation distances were not comparable within any proximity buffer, and neither were the individual network metrics generated from these matrices. This appears to be the first empirical evidence that observer presence and behaviour can influence the association patterns of habituated animals and thus have potentially significant impacts on measured social networks.