Night Capture of Roosting Cave Birds by Neanderthals: An Actualistic Approach

Evidence is accumulating on the regular and systematic Neanderthal exploitation of birds. However, the motivations, mechanisms, and circumstances underlying this behavior remains little explored despite their potential implications on Neanderthal ecology and capabilities. Fossil remains of choughs (Pyrrhocorax, Corvidae) are among the most abundant in cave sites with Mousterian technology. We reviewed the evidence showing that Neanderthals processed choughs for food, and confirmed that it occurred frequently over a widespread spatial and temporal scale. This lead us to propose the hypothesis that the cave-like refuge is the keystone resource connecting Neanderthals and choughs captured at night in rocky shelters eventually used by both species. By adopting an actualistic approach, we documented the patterns of refuge use and population dynamics of communally roosting choughs, the strategies and technology currently used to capture them, and their behavioral response against experimental human predators at night. Actualistic experiments showed that large numbers of choughs can be captured without highly sophisticated tools at night regularly and periodically, due to their occupation year-round during long-term periods of the same nocturnal shelters, the constant turnover of individuals, and their high site tenacity at these roost-sites even after recurrent disturbance and predation. Captures even with bare hands are further facilitated because choughs tend to flee confused into the cavity in darkness when dazzled and cornered by human (experimental) predators. Given the extreme difficulty of daylight chough capturing in open country, nocturnal hunting with the help of fire in the roosting caves and consumption in situ are proposed as the most plausible explanations for the strong association of choughs and Neanderthals in fossil assemblages. Night hunting of birds has implications for the social, anatomical, technological, and cognitive capacities of Neanderthals.

Suppression of personality variation in boldness during foraging in three-spined sticklebacks

Consistent inter-individual variation in behaviour within a population, widely referred to as personality variation, can be affected by environmental context. Feedbacks between an individual’s behaviour and state can strengthen (positive feedback) or weaken (negative feedback) individual differences when experiences such as predator encounters or winning contests are dependent on behavioural type. We examined the influence of foraging on individual-level consistency in refuge use (a measure of risk-taking, i.e. boldness) in three-spined sticklebacks, Gasterosteus aculeatus, and particularly whether changes in refuge use depended on boldness measured under control conditions. In the control treatment trials with no food, individuals were repeatable in refuge use across repeated trials, and this behavioural consistency did not differ between the start and end of these trials. In contrast, when food was available, individuals showed a higher degree of consistency in refuge use at the start of the trials versus controls but this consistency significantly reduced by the end of the trials. The effect of the opportunity to forage was dependent on behavioural type, with bolder fish varying more in their refuge use between the start and the end of the feeding trials than shyer fish, and boldness positively predicted the likelihood of feeding at the start but not at the end of the trials. This suggests a state-behaviour feedback, but there was no overall trend in how bolder individuals changed their behaviour. Our study shows that personality variation can be suppressed in foraging contexts and a potential but unpredictable role of feedbacks between state and behaviour. Significance statement In this experimental study, we examined how foraging influences consistency in risk-taking in individual three-spined sticklebacks. We show that bolder individuals become less consistent in their risk-taking behaviour than shyer individuals during foraging. Some bolder individuals reinforce their risk-taking behaviour, suggesting a positive feedback between state and behaviour, while others converge on the behaviour of shyer individuals, suggesting a negative feedback. In support of a role of satiation in driving negative feedback effects, we found that bolder individuals were more likely to feed at the start but not at the end of the trials. Overall, our findings suggest that foraging can influence personality variation in risk-taking behaviour; however, the role of feedbacks may be unpredictable.

­­Effect of multimodal cues from a predatory fish on refuge use and foraging on an amphidromous shrimp

Background Prey can alter their behavior when detecting predator cues. Little is known about which sensory channel, number of channels, or the interaction among channels that shrimp species use to evaluate the threat from predators. The amphidromous shrimp Xiphocaris elongata has an induced defense, an elongated rostrum, where predatory fishes are present. We sought to test if kairomones or visual cues when presented singly from fish either eating flakes or shrimp, had more effect on altering the temporal feeding and refuge use patterns of long-rostrum (LR) X. elongata. We were also interested in elucidating potential interactions among cues when presented simultaneously in different combinations (kairomones + visual + mechanosensory, kairomones + alarm + visual, kairomones + alarm, kairomones + visual) on the same response variables. We expected that when presented alone kairomones will significantly increase refuge use and decrease foraging, particularly late at night, in comparison to visual cues alone, and that multiple cues when presented simultaneously will further increase refuge use and decrease foraging at night. Methods We exposed shrimp to individual or multiple cues from the predatory fish mountain mullet, Augonostomus monticola. We examined shrimp behavior with respect to refuge use and foraging activity during four time periods (after sunset, nighttime, sunrise, and sunset) in a 24-hour period. Results Shrimp presented fish visual and chemical cues singly did not differ from one another but differed from control shrimp (no cues) with respect to refuge use or foraging. The number of shrimp using refuge in the treatment with most cues (KVM: kairomones+ visual + mechanosensory) was higher than in all the treatments with less cues. A significant decline in foraging was observed when multiple cues were presented simultaneously. The highest number of shrimp foraged one hour after sunset and at nighttime. A significant interaction was observed between cue treatments and time periods, with shrimp in the KVM treatment foraging less and using more refuge late at night and at sunrise than shrimp in other treatments or time periods. Conclusions The observation that fish chemical and visual cues when presented singly produced similar refuge use and foraging patterns was contrary to expectation and suggests that visual and chemical cues, when presented alone, provide redundant information to X. elongata with regards to predation threat. The significant increase in refuge use and reduction in foraging observed in the KVM treatment suggest multimodal signal enhancement in the perception of threat. This makes evolutionary sense in “noisy” environments, such as streams, where detection, localization, and intention of predators is much improved when cues are received through multiple sensory channels.

Behavioural responses to chemical cues of predators differ between fire salamander larvae from two different habitats

Predation is one of the strongest selection pressures, forcing prey organisms to detect predators and to display various antipredator behaviours, such as refuge-use or decreased activity. To recognise predators, chemosensory cues play a pivotal role, particularly in aquatic ecosystems. However, it is less known whether the ability to use these cues to respond with adequate antipredator behaviour varies between individuals occupying different habitats that are dissimilar in predation risk. Using field experiments, we examined antipredator behaviour of larval fire salamanders (Salamandra salamandra) from two different habitats, ponds and streams. Among other differences, ponds and streams are inhabited by habitat-specific predators, such as alpine newts (Ichthyosaura alpestris) occurring in ponds. We exposed larvae from both habitats to either chemical cues from alpine newts or a blank control (tap water) and investigated potential differences in their behavioural responses in two experiments. Pond larvae, but not stream larvae, became significantly less active when faced with chemical cues from newts compared to those faced with a control stimulus. Moreover, larvae from both habitats tested in water containing chemical cues spent significantly less time outside a shelter than those in control water. Our results demonstrate that larval fire salamanders recognise predatory newts through kairomones and alter their behaviour accordingly. However, experience with predatory newts may not be necessary to differentiate kairomones from control water, but may be beneficial for larvae to further develop their antipredator behaviour, thus representing conformance to a niche.

Fish avoid visually noisy environments that reduce their perceptual abilities

The environment contains different forms of ecological noise that can reduce the ability of animals to detect information. Here we ask whether animals can adapt their behaviour to either exploit or avoid areas of their environment with increased dynamic visual noise. By immersing three-spined sticklebacks (Gasterosteus aculeatus) into environments with a simulated form of naturally occurring visual noise – light bands created by the refraction of light from surface waves termed caustic networks – we tested how such visual noise affected the movements, habitat use, and perceptual abilities of these fish. Fish avoided areas of higher visual noise, and achieved this by increasing their activity as a function of the locally perceived noise level, resulting in individuals moving away from noisier areas. By projecting virtual prey into the environment with different levels of visual noise, we found that the fish’s ability to visually detect prey decreased as visual noise increased. We found no evidence that fish increased their exploration (and decreased their refuge use) in environments with increased visual noise, which would have been predicted if they were exploiting increased visual noise to reduce their own likelihood of being detected. Our results indicate that animals can use simple behavioural strategies to mitigate the impacts of dynamic visual noise on their perceptual abilities, thereby improving their likelihood of gathering information in dynamically changing and noisy environments.

State-behavior feedbacks suppress personality variation in boldness during foraging in sticklebacks

Consistent inter-individual variation within a population, widely referred to as personality variation, can be affected by environmental context. Feedbacks between an individual’s personality and state can strengthen (positive feedback) or weaken (negative feedback) individual differences when experiences such as predator encounters or winning contests are dependent on personality type. We examined the influence of foraging on individual-level consistency in refuge use (a measure of risk-taking, i.e. boldness) in three-spined sticklebacks, Gasterosteus aculeatus, and particularly whether changes in refuge use depended on boldness measured under control conditions. In the control treatment trials with no food, individuals were repeatable in refuge use across repeated trials, and this behavioral consistency did not differ between the start and end of these trials. In contrast, when food was available, individuals showed a higher degree of consistency in refuge use at the start of the trials versus controls but this consistency significantly reduced by the end of the trials. The effect of the opportunity to forage was dependent on personality, with bolder fish varying more in their refuge use between the start and the end of the feeding trials than shyer fish. This suggests a state-behavior feedback, but there was no overall trend in how individuals changed their behavior, with some individuals spending more, and others less, time in the refuge area at the end than at the start of the trials. Our study shows that personality variation can be suppressed in foraging contexts and a potential but unpredictable role of feedbacks between state and behavior.

Wild-born versus captive-bred: a comparison of survival and refuge selection by translocated numbats (Myrmecobius fasciatus)

ContextTo re-establish a population of the threatened numbat (Myrmecobius fasciatus) in a newly created safe haven at Mount Gibson Wildlife Sanctuary, in the semi-arid zone of Western Australia, wild-born and captive-bred individuals of both sexes were translocated. AimTo compare: (1) the use of refuges by wild-born numbats pre- and post-translocation, and (2) the survival and refuge use of captive-bred numbats compared with wild-sourced numbats post-translocation. MethodsMonitoring via radio-tracking facilitated the gathering of information on survival and behaviour of numbats pre- and post-translocation, and allowed a comparison of how different factors (e.g. captive-bred or wild-born; male or female) influenced survival and establishment in a new environment. Key resultsThere were no significant differences in survival between sexes or between wild-born and captive-bred individuals. However, there were some differences in behaviour between sexes and source populations. Captive-bred numbats, regardless of sex, made greater use of tree hollows as nocturnal refuges than did their wild-born counterparts. Among wild-born numbats, there was a comparatively greater use of tree hollows and logs on the ground by males at Mount Gibson than at Scotia. The use of diurnal escape refuges did not vary between sexes or between captive-bred and wild-born individuals. ConclusionsOn the basis of the information presented here, we conclude that, in the absence of predation by mammalian predators, and with suitable release habitat, captive-bred-to-wild translocations of numbats may be as likely to succeed as are wild-to-wild translocations, at least over the first few months post-translocation. ImplicationsOptimising the size and genetic diversity of the founding population by using animals from a variety of sources may not need to be heavily constrained by concerns about the ability of captive-bred numbats to adapt to and survive life in the wild.

Individual willingness to leave a safe refuge and the trade-off between food and safety: a test with social fish

Refuges offer prey animals protection from predation, but increased time spent hiding can reduce foraging opportunities. Within social groups, individuals vary in their refuge use and willingness to forage in the presence of a predator. Here, we examine the relative foraging benefits and mortality costs associated with individual refuge use and foraging behaviour within groups of goldfish ( Carassius auratus ) under predation risk from an avian predator (little egret— Egretta garzetta ). We assessed individual order of emergence from the refuge and participation over 15 group foraging outings, and assigned each fish a daily outing index score. The individual fish that emerged from the refuge earlier than the other group members and that participated in more outings received high outing index scores and consumed more food compared with fish that tended to emerge in posterior positions and participate in fewer outings. However, individual fish that attained high outing index scores suffered a higher risk of predation. Furthermore, the amount of time the egret spent at the pool affected group foraging behaviour: as predation risk increased, groups of fish consumed significantly less food. Our results exemplify the trade-off between foraging success and safety from predation that prey species regularly experience.