Proximity Of Predator Research Articles

Western Australian magpies respond to urgency information contained in conspecific alarm calls

Abstract Many animals provide information about predator proximity in their alarm calls. In response to predators further away, Western Australian magpies (Gymnorhina tibicen dorsalis) produce alarm calls containing fewer notes compared to those produced when predators are closer. Since the ability to make fine-scale adjustments to antipredator responses by being sensitive to the level of urgency in calls may be beneficial, receivers are expected to be able to appropriately decipher and respond to this information. We conducted playbacks to test whether magpies can respond to urgency information in conspecific alarm calls. Magpies were exposed to low-urgency calls (calls with one note), high-urgency calls (calls with four notes), and one- and four-note control calls. Receivers showed greater levels of responsiveness following playbacks of high-urgency calls compared to playbacks of low-urgency and control calls, providing evidence that magpies can respond to information about the urgency of a predator threat from conspecific alarm calls.

Prey tracking and predator avoidance in a Neotropical moist forest: a camera-trapping approach.

Whether prey species avoid predators and predator species track prey is a poorly understood aspect of predator-prey interactions, given measuring prey tracking by predators and predator avoidance by prey is challenging. A common approach to study these interactions among mammals in field situations is to monitor the spatial proximity of animals at fixed times, using GPS tags fitted to individuals. However, this method is invasive and only allows tracking of a subset of individuals. Here, we use an alternative, noninvasive camera-trapping approach to monitor temporal proximity of predator and prey animals. We deployed camera traps at fixed locations on Barro Colorado Island, Panama, where the ocelot (Leopardus pardalis) is the principal mammalian predator, and tested two hypotheses: (1) prey animals avoid ocelots; and (2) ocelots track prey. We quantified temporal proximity of predators and prey by fitting parametric survival models to the time intervals between subsequent prey and predator captures by camera traps, and then compared the observed intervals to random permutations that retained the spatiotemporal distribution of animal activity. We found that time until a prey animal appeared at a location was significantly longer than expected by chance if an ocelot had passed, and that the time until an ocelot appeared at a location was significantly shorter than expected by chance after prey passage. These findings are indirect evidence for both predator avoidance and prey tracking in this system. Our results show that predator avoidance and prey tracking influence predator and prey distribution over time in a field setting. Moreover, this study demonstrates that camera trapping is a viable and noninvasive alternative to GPS tracking for studying certain predator-prey interactions.

Is the urgency message encoded in heterospecific alarm calls perceived by domestic chickens?

AbstractVertebrate alarm calls can signal danger, and often encode information about predator proximity. Some species of birds alter the number of notes of their alarm calls to reflect urgency, with high‐urgency alarm calls having more notes than low‐urgency calls. Not only do individuals perceive the urgency message encoded in the alarm calls of conspecifics, but also in the alarm calls given by heterospecifics (sympatric and allopatric species). Yet, although well studied in wild species, the capacity to use heterospecific graded alarm call systems has not been investigated in domestic animals. Domestication may have altered the perceptual and communicative abilities of domestic species because they are less threatened by predators. Using playbacks conducted on domestic naked neck chickens (Gallus gallus domesticus) in France, we tested whether this species is able to decode information about urgency in alarm calls produced by a sympatric species; the common chaffinch (Fringilla coelebs), and by an allopatric species; the Australian magpie (Cracticus tibicen). We found the latency to resume foraging behaviour was higher after the high‐urgency call playbacks than the low‐urgency call playbacks, suggesting that the urgency encoded in heterospecific calls was perceived by chickens. However, results seem to indicate that the chickens are not able to discriminate between alarm and control (songs) sounds, but simply respond to specific sound characteristics of each playback stimulus. Our results raise some questions about how animals perceive and attend to information provided by heterospecific alarms. We hope this study will encourage future work with domesticated and nondomesticated animals.

Capybara responses to varying levels of predation risk

Predators can generate physiological and behavioural responses in prey individuals. Thus, carnivore reintroductions might cause profound changes in communities and ecosystems by modifying antipredator responses. Combining observational and experimental approaches, we compared the short- and long-term antipredator responses of capybaras, Hydrochoerus hydrochaeris , between a landscape with a high density of predators (Pantanal, Brazil) and a landscape where predators became extinct in the mid-20th century but where a jaguar reintroduction project was in progress (Iberá, Argentina). Generalized linear models were used to test whether the presence of natural predators affects capybara behavioural budgets, gregarious behaviour and the associated physiological stress responses and to test whether, in the short term, capybaras increase their vigilance levels after detecting the proximity of a simulated predator (a playback of jaguar, Panthera onca , calls). Capybaras in the Pantanal did not show higher levels of vigilance but they spent a greater proportion of time foraging than did capybaras in Iberá. Pantanal groups were smaller and foraged closer to water. The baseline levels of stress hormones tended to be higher in Iberá. In response to simulated stimuli, both populations responded to predator sound cues by increasing vigilance, but Iberá groups also increased vigilance in response to a control sound, suggesting that they did not recognize the predator stimulus as a greater risk than another stimulus. In areas with predators, capybaras may reduce predation risk by choosing safer areas, where they can spend more time foraging when predators are not nearby. Vigilance may be only a reactive response to cues of the predator's proximity. Understanding the capybara's antipredator responses may help predict the potential effects and the success of jaguar reintroduction in a region where the jaguar has been absent for over 80 years. • Capybaras facing regular jaguar predation spent more time foraging in safe zones. • Capybaras living without predators did not recognize predator sound stimuli. • Vigilance may be only a reactive response to cues of the predator's proximity. • Prey released from predation for generations may lose some antipredator behaviours. • Naïvety and high density of capybaras could predict successful jaguar reintroduction.

Drop when the stakes are high: adaptive, flexible use of dropping behaviour by aphids

Abstract For herbivorous insects, dropping from the host plant is a commonly-observed antipredator defence. The use of dropping compared to other behaviours and its timing in relation to contact with a predator was explored in both pea aphids (Acyrthosiphon pisum) and potato aphids (Macrosiphum euphorbiae). Pea aphids dropped more frequently in response to ladybird adults (Adalia bipunctata) than lacewing larvae (Chrysoperla carnea). Potato aphids mainly walked away or backed-up in response to both predator types; but they dropped more frequently relative to other non-walking defences when faced with ladybird adults. Contact with a predator was an important influencer of dropping for both species, and most drops occurred from adjacent to the predator. Dropping appears to be a defence adaptively deployed only when the risk of imminent predation is high; factors that increase dropping likelihood include presence of faster-foraging predators such as adult ladybirds, predator proximity, and contact between aphid and predator.

Sedative and analgesic potentials of dexmedetomidine gluconate using constant rate infusion technique in rabbit

Rabbits are easily stressed. Stress can be caused by pain, disease, unfamiliar surroundings, transport, rough handling or proximity of potential predators. Thus, this study was conceived to evaluate the effective sedative and analgesic doses of dexmedetomide gluconate in rabbits using the constant rate infusion (CRI) technique. Eight healthy adult New Zealand White rabbits with an average weight of 1.93 ± 0.33kg were used for the study. They were starved of feed for three hours before the experiment but were supplied water sufficiently. The CRI infusion was prepared by adding 1mcgkg-1 into 500mL bags of lactated ringer's solution. Each rabbit received an initial dose of 20mcgkg-1 dexmedetomidine® intramuscularly at the thigh muscle. Venous access was secured fifteen minutes later and the fluid prepared for CRI was connected to the cannular, the fluid was set to flow at daily fluid maintenance rate of 90mlkgday-1 for one hour. The procedure was repeated replacing 20mcgkg-1 with 40mcgkg-1. Neither sedation nor analgesia was achieved with 20mcgkg-1 dexmedetomidine® while 40mcgkg-1 gave mild to moderate sedation, however, no analgesic effect was observed with the two dose regimes. In conclusion, sedation was achieved with 40mcgkg-1 but no analgesic effect was achieved in both doses used.

Nest-site selection and breeding success of passerines in the world's southernmost forests.

BackgroundBirds can maximize their reproductive success through careful selection of nest-sites. The ‘total-foliage’ hypothesis predicts that nests concealed in vegetation should have higher survival. We propose an additional hypothesis, the ‘predator proximity’ hypothesis, which states that nests placed farther from predators would have higher survival. We examined these hypotheses in the world’s southernmost forests of Navarino Island, in the Cape Horn Biosphere reserve, Chile (55°S). This island has been free of mammalian ground predators until recently, and forest passerines have been subject to depredation only by diurnal and nocturnal raptors.MethodsDuring three breeding seasons (2014–2017), we monitored 104 nests for the five most abundant open-cup forest-dwelling passerines (Elaenia albiceps, Zonotrichia capensis, Phrygilus patagonicus, Turdus falcklandii, and Anairetes parulus). We identified nest predators using camera traps and assessed whether habitat characteristics affected nest-site selection and survival.ResultsNest predation was the main cause of nest failure (71% of failed nests). Milvago chimango was the most common predator, depredating 13 (87%) of the 15 nests where we could identify a predator. By contrast, the recently introduced mammal Neovison vison, the only ground predator, depredated one nest (7%). Species selected nest-sites with more understory cover and taller understory, which according to the total-foliage hypothesis would provide more concealment against both avian and mammal predators. However, these variables negatively influenced nest survival. The apparent disconnect between selecting nest-sites to avoid predation and the actual risk of predation could be due to recent changes in the predator assemblage driven by an increased abundance of native M. chimango associated with urban development, and/or the introduction of exotic mammalian ground predators to this island. These predator assemblage changes could have resulted in an ecological trap. Further research will be needed to assess hypotheses that could explain this mismatch between nest-site selection and nest survival.

Prey colonization in freshwater landscapes can be stimulated or inhibited by the proximity of remote predators.

Recent findings suggest that the colonization of habitat patches may be affected by the quality of surrounding patches. For instance, patches that lack predators may be avoided when located near others with predators, a pattern known as risk contagion. Alternatively, predator avoidance might also redirect dispersal towards nearby predator-free patches resulting in so-called habitat compression. However, it is largely unknown how predators continue to influence these habitat selection behaviours at increasing distances from outside of their own habitat patch. In addition, current information is derived from artificial mesocosm experiments, while support from natural ecosystems is lacking. This study used bromeliad landscapes as a natural model system to study how oviposition habitat selection of Diptera responds to the cues of a distant predator, the carnivorous elephant mosquito larva. We established landscapes containing predator-free bromeliad habitat patches placed at increasing distances from a predator-containing patch, along with replicate control landscapes. These patches were then left to be colonized by ovipositing bromeliad insects. We found that distance to predators modulates habitat selection decisions. Moreover, different dipteran families had different responses suggesting different habitat selection strategies. In some families, predator-free patches at certain distances from the predator patch were avoided, confirming risk contagion. In other families, these patches received higher numbers of colonists providing evidence of predator-induced habitat compression. We confirm that effects of predators in a natural ecosystem can extend beyond the patch in which the predator is present and that the presence or absence of remote predator effects on habitat selection depends on the distance to predators. The notion that perceived habitat quality can depend on conditions in neighbouring patches forces habitat selection studies to adopt a landscape perspective and account for the effects of both present and remote predators when explaining community assembly in metacommunities.

Larval newts adjust foraging rate to perceived predator and competitor proximity

Foraging is key for most animals, because their energy and matter income depend on food ingestion. However, animals may respond adaptively to perceived competitor and/or predator proximity by modifying their foraging rates. Increased foraging activity is expected to improve the chances of succeeding in competition. However, the benefits of increased foraging activity could be offset by the risks of increased conspicuousness to predators. Plus, starvation may have counteracting or additive effects on foraging behaviour. Here, we test these hypotheses in larval Iberian ribbed newts (Pleurodeles waltl). We estimated foraging rates of individuals haphazardly assigned to either a restricted or an unrestricted-feeding regime, in water with (1) self-odour as control, (2) predator Dytiscus sp. chemical cues, and (3) competitor conspecific larva chemical cues. Treatments were presented in a random sequence. Newt larvae responded to either predator or conspecific chemical cues by increasing foraging rates relative to the control. Conspecific chemical cues increased foraging rates over the other two treatments. Feeding regime did not modify larva response to perceived predator and competitor proximity. Increased foraging rates in the presence of conspecific chemical cues could simultaneously improve larval energetic status to face competition and reduce prey available for the competitor. Intermediate foraging rates in the presence of predator chemical cues suggest a trade-off between the benefits (likely improved energetic status or accelerated metamorphosis) and the costs (likely increased conspicuousness) of increased food ingestion. These results prove that larval newts adjust foraging rates to perceived predator and competitor proximity.

Complex habitat patterns create unpredictable nest predation risk – an artificial nest experiment

Although birds might increase nesting survival by selecting safe sites, nest predation is a major limiting factor in natural bird populations. We investigated how forest structure, predator distribution, and nest location contribute to nest predation risk, and whether lower predation probabilities characterize formerly “safe” sites. We distributed 304 artificial ground and tree nests in a forest landscape, following the previous year locations of forest grouse observations (with and without broods). We modelled nest predation incidence using generalized mixed models; we also identified potential nest predators by tooth/bill marks on plasticine eggs. We found complex habitat effects: nest predation depended non-linearly on the stand age (low risk in post-clear-cut stands; peak values in middle-aged stands) and there were no simple relationships with predator proximity or nest concealment. Predation probabilities were higher in tree nests than in ground nests, and did not differ in the locations where broods had been observed or not.

Sound repetition rate controls the duration of tonic immobility in chicks (Gallus gallus)

Tonic Immobility (TI) functions as anti-predator defense. Its duration depends on cues signaling predator proximity. One such cue includes alarm calls from conspecifics and non-conspecifics. This study aimed to determine the cue within alarm calls that controls TI duration. We induced TI in chicks (Gallus gallus) and found that their TI durations increased in the presence of adult conspecific alarm calls, non-conspecific alarm calls, and synthetic sounds made of white noise set to the repetition rate found in natural alarm calls. Moreover, chicks did not increase their TI durations when exposed to conspecific attraction calls, synthetic sounds made of white noise set to the repetition rate found in natural attraction calls, and derived sounds made of a natural alarm call lacking an internote interval. We then created: 1) sounds with white noise set to the internote interval found in natural alarm calls and the note duration found in natural attraction calls, and 2) sounds with white noise set to the internote interval found in natural attraction calls and the note duration found in natural alarm calls. Neither affected TI duration. We conclude that repetition rate acts as a salient cue that lengthens TI duration.

Human-attacks by an urban raptor are tied to human subsidies and religious practices

Growing urbanization is increasing human-wildlife interactions, including attacks towards humans by vertebrate predators, an aspect that has received extremely scarce investigation. Here, we examined the ecological, landscape and human factors that may promote human-aggression by raptorial Black kites Milvus migrans in the 16-millions inhabitants megacity of Delhi (India). Physical attacks depended on human activities such as unhygienic waste management, ritual-feeding of kites (mainly operated by Muslims), human density, and presence of a balcony near the nest, suggesting an association between aggression and frequent-close exposure to humans and derived food-rewards. Surprisingly, while more than 100,000 people could be at risk of attack in any given moment, attitudes by local inhabitants were strikingly sympathetic towards the birds, even by injured persons, likely as a result of religious empathy. These results highlight the importance of socio-cultural factors for urban biota and how these may radically differentiate the under-studied cities of developing countries from those of western nations, thus broadening our picture of human-wildlife interactions in urban environments. The rapid sprawling of urban and suburban areas with their associated food-subsidies is likely to increase proximity and exposure of large predators to humans, and vice versa, leading to heightened worldwide conflicts.

Birds orient their heads appropriately in response to functionally referential alarm calls of heterospecifics

Vertebrate alarm calls signal danger and often encode graded or categorical information about predator proximity or type. In addition to allowing communication with conspecifics, alarm calls are a valuable source of information for eavesdropping heterospecifics. However, although eavesdropping has been experimentally demonstrated in over 70 species, we know little about exactly what information eavesdroppers gain from heterospecific alarm calls. Here, we investigated whether Australian magpies, Cracticus tibicen, extract relevant information about the type of threat from functionally referential alarm calls given by noisy miners, Manorina melanocephala. Miner aerial alarm calls signal a predator in flight, whereas mobbing calls signal a terrestrial or perched predator. We therefore tested whether magpies gain information on the elevation of expected danger. We first confirmed, by measuring bill angles on video, that magpie head orientation changes appropriately with differences in the elevation of a conspicuous moving object. We then conducted a field experiment that measured magpie bill angle in response to playback of miner aerial and mobbing alarm calls. The maximum and mean bill angles were higher in response to aerial than to mobbing calls, suggesting that magpies use information from miner alarms to search visually at appropriate elevations for the specific type of danger. Magpies were also vigilant for longer after aerial alarm calls that followed mobbing calls, implying perception of an escalating threat level. Our work shows that individuals can gain information on the type or location of danger from heterospecific alarm calls, which is likely to increase the effectiveness of antipredator responses.

Identification of possible nutritional and stress risk factors in the development of marmoset wasting syndrome.

Marmoset wasting syndrome (MWS) describes a series of symptoms in callitrichids that lead to general weakness and a failure to thrive in captive conditions such as zoological institutions. Though the cause of MWS has not been identified, the majority of hypotheses are linked to deficiencies of specific nutrients and increased stress levels. Questionnaires were sent to zoos requesting information on diets and housing of currently living and dead callitrichids before their deaths, as well as their postmortem reports. Risk factors for development and occurrence of MWS include close proximity of predator enclosures and high levels of dietary magnesium and zinc. Variables with effects which may protect against the development of MWS included provision of a nest box, natural trees within enclosure, reduced visibility to visitors, as well as dietary factors such as higher concentrations of potassium and fiber fractions. The protective effects of limited concentrate feeds and increased total dietary fiber may help reduce the risks of developing MWS. The minerals may not have biological implications in MWS per se, however, they may be reflective of diets too high in concentrates and too low in plant matter. Habitat designs that are less naturalistic and those which provide insufficient privacy or hide areas may increase chronic stress for callitrichid species, possibly because of visitor-related stress. Other causes of chronic stress in captive zoo populations should be the topic of further research to reduce occurrence of MWS.

Honest error, precaution or alertness advertisement? Reactions to vertebrate pseudopredators in red‐nosed cuxiús (Chiropotes albinasus), a high‐canopy neotropical primate

AbstractPredation on primates is considered to have far‐reaching effects on the foraging and social ecology of a species. Primate species display a variety of responses to predator proximity and attack, ranging from active physical defense and mobbing, to flight and concealment. Warning calls are often given, and potentially threatening animals may be tracked, either actively or with head movements. Such behaviors take time that could be used for other activities. Accordingly, there should be strong selection to respond only to those species that represent a genuine threat. However, primates give defense‐based behaviors to non‐predator species. We tested the hypotheses that responses to pseudopredators are (i) precautionary calls made by individuals following the Dinner/Life Principle, or (ii) represent the ontogeny of species recognition. Of the species that ellicted a response from the cuxiús, 80% resembled a primate predator; 95% of the encounters that elicited a response from the cuxiús occurred when the distance between the pseudopredator and cuxiús was ≤20 m. In regard to the frequency of responses to pseudopredators, we found no difference between adults and juveniles (47.6% and 52.4%, respectively) and no differences between adult males and adult females (60% and 40% of the responses, respectively). However, reactions to pseudopredators were of shorter duration ( ± standard error (SE): 42.2 ± 15.9 s) than were reactions to actual predator species ( ± SE: 1,024.3 ± 329.1 s). There were only three instances where alarm calls were made to species that did not resemble predators, and 66.7% (N = 2) were made by adult cuxiús and only 33.3% (N = 1) were made by a juvenile cuxiú. Therefore, we found partial support for the Dinner/Life Principle hypothesis, but no support for the ontogeny hypothesis. Examination of such responses to pseudopredators in other primate and non‐primate species may help understand the evolution of such behaviors.

Chemosensory adaptations of the mountain fly Drosophila nigrosparsa (Insecta: Diptera) through genomics\u2019 and structural biology\u2019s lenses

Chemoreception is essential for survival. Some chemicals signal the presence of nutrients or toxins, others the proximity of mating partners, competitors, or predators. Chemical signal transduction has therefore been studied in multiple organisms. In Drosophila species, a number of odorant receptor genes and various other types of chemoreceptors were found. Three main gene families encode for membrane receptors and one for globular proteins that shuttle compounds with different degrees of affinity and specificity towards receptors. By sequencing the genome of Drosophila nigrosparsa, a habitat specialist restricted to montane/alpine environment, and combining genomics and structural biology techniques, we characterised odorant, gustatory, ionotropic receptors and odorant binding proteins, annotating 189 loci and modelling the protein structure of two ionotropic receptors and one odorant binding protein. We hypothesise that the D. nigrosparsa genome experienced gene loss and various evolutionary pressures (diversifying positive selection, relaxation, and pseudogenisation), as well as structural modification in the geometry and electrostatic potential of the two ionotropic receptor binding sites. We discuss possible trajectories in chemosensory adaptation processes, possibly enhancing compound affinity and mediating the evolution of more specialized food, and a fine-tuned mechanism of adaptation.

Prey reduce risk-taking and abundance in the proximity of predators.

Prey have evolved anti-predator defences that reduce or eliminate the risk of predation. Predators often reproduce at specific sites over many years causing permanent threats to local prey species. Such prey may respond by moving elsewhere thereby reducing local population abundance, or they may stay put and adjust their behavior to the presence of predators. We tested these predictions by analyzing population abundance and anti-predator behavior within 100 m of and 500 m away from nests of sparrowhawks Accipiter nisus and goshawks A. gentilis for 80 species of birds. Population abundance of prey was reduced by 11% near goshawk nests and by 15% near sparrowhawk nests when compared with nearby control sites in similar habitats. Flight initiation distance (FID) of prey, estimated as the distance at which birds took flight when approached by a human, increased by 50% in the presence of hawk nests, providing evidence of adjustment of anti-predator behavior to prevailing risks of predation. Susceptibility to predation was estimated as log transformed abundance of the observed number of prey items obtained from prey remains collected around nests minus log transformed expected number of prey according to point counts of breeding birds. FID increased from 10 to 46 m with increasing susceptibility of prey species to predation by the goshawk and from 12 to 15 m with increasing susceptibility of prey species to predation by the sparrowhawk. These findings suggest that prey adjust their distribution and anti-predator behavior to the risk of predation.

Breeding in a den of thieves: pros and cons of nesting close to egg predators

AbstractBreeding success of many Arctic‐breeding bird populations varies with lemming cycles due to prey switching behavior of generalist predators. Several bird species breed on islands to escape from generalist predators like Arctic fox Vulpes lagopus, but little is known about how these species interact. We studied brent geese Branta bernicla bernicla that share islands with gulls (Larus spec.) in Taimyr, Siberia (Russia). On one hand, gulls are egg predators, which occasionally steal an egg when incubating geese leave the nest for foraging bouts. On the other hand, gulls import marine resources to the islands, enriching the soil with their guano. We considered three hypotheses regarding clutch size of brent geese after partial nest predation. According to the “predator proximity hypothesis”, clutch size is expected to be smallest close to gulls, because of enhanced predator exposure. Conversely, clutch size is expected to be largest close to gulls, because of the supposedly better feeding conditions close to gulls, which might reduce nest recess times of geese and hence egg predation risk (“guano hypothesis”). Furthermore, gulls may defend their nesting territory, and thus nearby goose nests might benefit from this protection against other gulls (“nest association hypothesis”). We mapped goose and gull nests toward the end of the goose incubation period. In accordance with the latter two hypotheses, goose clutch size decreased with distance to the nearest gull nest in all but the lemming peak year. In the lemming peak year, clutch size was consistently high, indicating that partial nest predation was nearly absent. By mapping food quantity and quality, we found that nitrogen availability was indeed higher closer to gull nests, reflecting guanofication. Unlike predicted by the nest association hypothesis, a predation pressure experiment revealed that egg predation rate decreased with distance to the focal gull nests. We therefore propose that higher food availability close to gulls enables female geese to reduce nest recess time, limiting egg predation by gulls.

Lion proximity, not moon phase, affects the nocturnal movement behaviour of zebra and wildebeest

AbstractMoon phase affects nocturnal activity patterns in mammals. Among ungulates, a number of studies have found animals to be more active over full moon nights. This may be because increased luminosity provides increased opportunity to forage and/or increased ability to detect predators; known as the visual acuity hypothesis. Here, we use GPS‐derived movement data to test for the influence of moon phase on plains zebra Equus quagga and blue wildebeest Connochaetes taurinus activity in Kruger National Park, South Africa. We compare animal movement (rate and displacement) over full and new moon nights, and consider the effect of lion proximity. We found that lion proximity largely determined the nocturnal movements of zebra and wildebeest, not moon phase. When lions were >1 km away, there was no difference in the nocturnal movement activity of prey animals over full and new moon conditions, contradicting previous findings. When lions were within 1 km of these animals, however, the movement of zebra and wildebeest greatly increased over the new moon, the relatively dark period when lion were most likely hunting. Although we could not explicitly test for predator detection here, our findings suggest that the visual acuity hypothesis does not hold for zebra and wildebeest in Kruger National Park (KNP) given that there is no evidence for increased foraging activity over the full moon. The influence of moon phase on the nocturnal activity of African ungulates may be more complicated than anticipated, and we suggest that this cannot be estimated unless predator proximity is accounted for.

Plastic response of fearful prey to the spatiotemporal dynamics of predator distribution.

Ecological theory predicts that the intensity of antipredator responses is dependent upon the spatiotemporal context of predation risk (the risk allocation hypothesis). However, most studies to date have been conducted over small spatial extents, and did not fully take into account gradual responses to predator proximity. We simultaneously collected spatially explicit data on predator and prey to investigate acute responses of a threatened forest ungulate, the boreal caribou (Rangifer tarandus), to the spatiotemporal dynamics of wolf (Canis lupus) distribution during spring. Movement analysis of GPS-collared individuals from both species revealed high plasticity in habitat-selection decisions of caribou. Female caribou avoided open areas and deciduous forests and moved relatively fast and toward foraging areas when wolves were closer than 2.5 km. Caribou also avoided food-rich areas only when wolves were within 1 km. Our results bridge the gap between long-term perceived risk and immediate flight responses by revealing dynamic antipredator tactics in response to predator proximity.