Reactive anti-predator behavioral strategy shaped by predator characteristics

Large mammalian herbivores use a diverse array of strategies to survive predator encounters including flight, grouping, vigilance, warning signals, and fitness indicators. While anti-predator strategies appear to be driven by specific predator traits, no prior studies have rigorously evaluated whether predator hunting characteristics predict reactive anti-predator responses. We experimentally investigated behavioral decisions made by free-ranging impala, wildebeest, and zebra during encounters with model predators with different functional traits. We hypothesized that the choice of response would be driven by a predator’s hunting style (i.e., ambush vs. coursing) while the intensity at which the behavior was performed would correlate with predator traits that contribute to the prey’s relative risk (i.e., each predator’s prey preference, prey-specific capture success, and local predator density). We found that the choice and intensity of anti-predator behaviors were both shaped by hunting style and relative risk factors. All prey species directed longer periods of vigilance towards predators with higher capture success. The decision to flee was the only behavior choice driven by predator characteristics (capture success and hunting style) while intensity of vigilance, frequency of alarm-calling, and flight latency were modulated based on predator hunting strategy and relative risk level. Impala regulated only the intensity of their behaviors, while zebra and wildebeest changed both type and intensity of response based on predator traits. Zebra and impala reacted to multiple components of predation threat, while wildebeest responded solely to capture success. Overall, our findings suggest that certain behaviors potentially facilitate survival under specific contexts and that prey responses may reflect the perceived level of predation risk, suggesting that adaptive functions to reactive anti-predator behaviors may reflect potential trade-offs to their use. The strong influence of prey species identity and social and environmental context suggest that these factors may interact with predator traits to determine the optimal response to immediate predation threat.

Learning steers the ontogeny of an efficient hunting sequence in zebrafish larvae

Goal-directed behaviors may be poorly coordinated in young animals but, with age and experience, behavior progressively adapts to efficiently exploit the animal’s ecological niche. How experience impinges on the developing neural circuits of behavior is an open question. We have conducted a detailed study of the effects of experience on the ontogeny of hunting behavior in larval zebrafish. We report that larvae with prior experience of live prey consume considerably more prey than naive larvae. This is mainly due to increased capture success and a modest increase in hunt rate. We demonstrate that the initial turn to prey and the final capture manoeuvre of the hunting sequence were jointly modified by experience and that modification of these components predicted capture success. Our findings establish an ethologically relevant paradigm in zebrafish for studying how the brain is shaped by experience to drive the ontogeny of efficient behavior.

Modified live traps increase capture success of semifossorial voles in Alpine meadows

Live-trapping of rodents is facilitated by their thigmotaxis (i.e. the tendency to walk along linear structures of the habitat). However, in open habitats, such as meadows and prairies, where linear structures (e.g. rocks and fallen branches) are generally absent and where densities are likely to be low, capturing rodents is often very demanding or ineffective. This applies especially to semifossorial small mammals. Therefore, we developed a technique to increase the capture success of these rodents in Alpine meadows. We applied a box in Tetrapak® with the perforated floor at the opening of Sherman traps. Semifossorial voles (Microtus spp.), leaving their burrows, would remain in a confined status, in the dark within the Tetrapak®, being forced to enter the trap or to go back in the tunnel. Sherman traps modified with Tetrapak® were positioned immediately upon active burrows, alternating with the same number of unmodified traps. Then, we compared the number of captures with and without this modification. Two trapping sessions were carried out, for 3 days/site each, in eight sites (totally 2784 trap-days). Overall, 55 semifossorial voles were trapped; 41 (74.6%) were caught in modified traps, showing that they increase the capture success of semifossorial voles in Alpine meadows.

Temperature and Estrogen Alter Predator–Prey Interactions between Fish Species

Synopsis A variety of environmental estrogens are commonly detected in human-impacted waterways. Although much is known about the effects of these environmental estrogens on the reproductive physiology and behavior of individuals within species, comparatively less is known about how these compounds alter the outcomes of interactions between species. Furthermore, few studies have considered how the effects of contaminants are modulated by natural variation in abiotic factors, such as temperature. To help fill this knowledge gap, we conducted a factorial experiment to examine the independent and combined effects of estrone (E1) and temperature on the outcome of predator–prey interactions between two common North American freshwater fishes, fathead minnows (Pimephales promelas) and bluegill sunfish (Lepomis macrochirus). Larval fathead minnows and adult sunfish were exposed to either a low (mean±standard deviation, 90.1 ± 18 ng/L; n = 16) or high (414 ± 147 ng/L; n = 15) concentration of E1 or to a solvent control for 30 days at one of four natural seasonal temperatures (15°C, 18°C, 21°C, and 24°C) before predation trials were performed. Exposure to E1 was associated with a significant increase in larval predation mortality that was independent of temperature. Across all temperature treatments, approximately 74% of control minnows survived; this survivorship significantly exceeded that of minnows exposed to either concentration of E1 (49% and 53% for minnows exposed to the low and high concentrations, respectively). However, exposure to E1 also impaired the prey-capture success of sunfish, partially mitigating predation pressure on exposed minnows. Overall prey-capture success by sunfish showed an inverted U-shaped distribution with temperature, with maximal prey consumption occurring at 21°C. This study illustrates the vulnerability of organismal interactions to estrogenic pollutants and highlights the need to include food web interactions in assessments of risk.

Effects of different attractants and human scent on mesocarnivore detection at camera traps

ContextCamera traps paired with baits and scented lures can be used to monitor mesocarnivore populations, but not all attractants are equally effective. Several studies have investigated the efficacy of different attractants on the success of luring mesocarnivores to camera traps; fewer studies have examined the effect of human scent at camera traps. AimsWe sought to determine the effects of human scent, four attractants and the interaction between attractants and human scent in luring mesocarnivores to camera traps. Methods We compared the success of synthetic fermented egg (SFE), fatty acid scent (FAS) tablets, castor oil, and sardines against a control of no attractant in luring mesocarnivores to camera traps. We deployed each attractant and the control with either no regard to masking human scent or attempting to restrict human scent for a total of 10 treatments, and replicated treatments eight to nine times in two different phases. We investigated whether: (1) any attractants increased the probability of capturing a mesocarnivore at a camera trap; (2) not masking human scent affected the probability of capturing a mesocarnivore at a camera trap; and (3) any attractants increased the probability of repeat detections at a given camera trap. We also analysed the behaviour (i.e. speed and distance to attractant) of each mesocarnivore in relation to the attractants. Key resultsSardines improved capture success compared with the control treatments, whereas SFE, castor oil, and FAS tablets had no effect when all mesocarnivores were included in the analyses. Masking human scent did not affect detection rates in the multispecies analyses. Individually, the detection of some species depended on the interactions between masking (or not masking) human scent and some attractants. ConclusionsSardines were the most effective as a broad-based attractant for mesocarnivores. Mesocarnivores approached traps baited with sardines at slower rates, which allows for a higher success of capturing an image of the animal. ImplicationsHuman scent may not need to be masked when deploying camera traps for multispecies mesocarnivore studies, but researchers should be aware that individual species respond differently to attractants and may have higher capture success with species-specific attractants.

Learning steers the ontogeny of an efficient hunting sequence in zebrafish larvae

The success of goal-directed behaviours relies on the coordinated execution of a sequence of component actions. In young animals, such sequences may be poorly coordinated, but with age and experience, behaviour progressively adapts to efficiently exploit the animal’s ecological niche. How experience impinges on the developing neural circuits of behaviour is an open question. As a model system, larval zebrafish (Danio rerio) hold enormous potential for studying both the development of behaviour and the underlying circuits, but no relevant experience-dependent learning paradigm has yet been characterized. To address this, we have conducted a detailed study of the effects of experience on the ontogeny of hunting behaviour in larval zebrafish. We report that larvae with prior prey experience consume considerably more prey than naive larvae. This is mainly due to increased capture success that is also accompanied by a modest increase in hunt rate. We identified two components of the hunting sequence that are jointly modified by experience. At the onset of the hunting sequence, the orientation strategy of the turn towards prey is modified such that experienced larvae undershoot prey azimuth. Near the end of the hunt sequence, we find that experienced larvae are more likely to employ high-speed capture swims initiated from longer distances to prey. Combined, these modified turn and capture manoeuvrers can be used to predict the probability of capture success and suggest that their development provides advantages specific to larvae feeding on live-prey. Our findings establish an ethologically relevant paradigm in zebrafish for studying how the brain is shaped by experience to drive the ontogeny of efficient behaviour.

Foraging innovation in an artificial environment: a case of little egret luring prey goldfish through beak dipping

Behavioural innovations play an important role in animal ecology and evolution. We report a case of little egret using its beak dips as a tool to lure and catch prey goldfish in an artificial environment designed to test predator–prey behavioural foraging games. The egret mimicked the food pellets falling into the pool from a mechanical feeder that fed the goldfish at regular intervals. The falling pellets created ripples in the water that acted as a cue for the prey goldfish to come out of the cover and feed on the floating pellets. The egret learned this phenomenon through time and used its beak dips to create ripples and attract the prey outside. The egret preferably used the location of the feeder in the pool to carry out its beak dipping attempts and maximize its fish capture success. The egret attempted this behaviour more in the largest cover that provided the best refuge to the prey goldfish. The egret beak dipping attempts to lure the prey goldfish out of the cover declined through experimental time as well as with increasing prey kills. As the beak dipping behaviour did not result in a high capture rate of fish, the egret subsequently reduced its attempts through time. This case study illustrates that foraging innovations can occur through learning in laboratory conditions containing a novel but artificial environment.