Investigating differences in vigilance tactic use within and between the sexes in eastern grey kangaroos

Peer reviewedPostprin

Collective Animal Behavior from Bayesian Estimation and Probability Matching

Animals living in groups make movement decisions that depend, among other factors, on social interactions with other group members. Our present understanding of social rules in animal collectives is based on empirical fits to observations and we lack first-principles approaches that allow their derivation. Here we show that patterns of collective decisions can be derived from the basic ability of animals to make probabilistic estimations in the presence of uncertainty. We build a decision-making model with two stages: Bayesian estimation and probabilistic matching.
In the first stage, each animal makes a Bayesian estimation of which behavior is best to perform taking into account personal information about the environment and social information collected by observing the behaviors of other animals. In the probability matching stage, each animal chooses a behavior with a probability given by the Bayesian estimation that this behavior is the most appropriate one. This model derives very simple rules of interaction in animal collectives that depend only on two types of reliability parameters, one that each animal assigns to the other animals and another given by the quality of the non-social information. We test our model by obtaining theoretically a rich set of observed collective patterns of decisions in three-spined sticklebacks, Gasterosteus aculeatus, a shoaling fish species. The quantitative link shown between probabilistic estimation and collective rules of behavior allows a better contact with other fields such as foraging, mate selection, neurobiology and psychology, and gives predictions for experiments directly testing the relationship between estimation and collective behavior

Effects of Reproductive Status, Social Rank, Sex and Group Size on Vigilance Patterns in Przewalski's Gazelle

Quantifying vigilance and exploring the underlying mechanisms has been the subject of numerous studies. Less attention has focused on the complex interplay between contributing factors such as reproductive status, social rank, sex and group size. Reproductive status and social rank are of particular interest due to their association with mating behavior. Mating activities in rutting season may interfere with typical patterns of vigilance and possibly interact with social rank. In addition, balancing the tradeoff between vigilance and life maintenance may represent a challenge for gregarious ungulate species rutting under harsh winter conditions. We studied vigilance patterns in the endangered Przewalski's gazelle (Procapra przewalskii) during both the rutting and non-rutting seasons to examine these issues.Field observations were carried out with focal sampling during rutting and non-rutting season in 2008-2009. Results indicated a complex interplay between reproductive status, social rank, sex and group size in determining vigilance in this species. Vigilance decreased with group size in female but not in male gazelles. Males scanned more frequently and thus spent more time vigilant than females. Compared to non-rutting season, gazelles increased time spent scanning at the expense of bedding in rutting season. During the rutting season, territorial males spent a large proportion of time on rutting activities and were less vigilant than non-territorial males. Although territorial males may share collective risk detection with harem females, we suggest that they are probably more vulnerable to predation because they seemed reluctant to leave rut stands under threats.Vigilance behavior in Przewalski's gazelle was significantly affected by reproductive status, social rank, sex, group size and their complex interactions. These findings shed light on the mechanisms underlying vigilance patterns and the tradeoff between vigilance and other crucial activities

How Group Size Affects Vigilance Dynamics and Time Allocation Patterns: The Key Role of Imitation and Tempo

In the context of social foraging, predator detection has been the subject of numerous studies, which acknowledge the adaptive response of the individual to the trade-off between feeding and vigilance. Typically, animals gain energy by increasing their feeding time and decreasing their vigilance effort with increasing group size, without increasing their risk of predation (‘group size effect’). Research on the biological utility of vigilance has prevailed over considerations of the mechanistic rules that link individual decisions to group behavior. With sheep as a model species, we identified how the behaviors of conspecifics affect the individual decisions to switch activity. We highlight a simple mechanism whereby the group size effect on collective vigilance dynamics is shaped by two key features: the magnitude of social amplification and intrinsic differences between foraging and scanning bout durations. Our results highlight a positive correlation between the duration of scanning and foraging bouts at the level of the group. This finding reveals the existence of groups with high and low rates of transition between activies, suggesting individual variations in the transition rate, or ‘tempo’. We present a mathematical model based on behavioral rules derived from experiments. Our theoretical predictions show that the system is robust in respect to variations in the propensity to imitate scanning and foraging, yet flexible in respect to differences in the duration of activity bouts. The model shows how individual decisions contribute to collective behavior patterns and how the group, in turn, facilitates individual-level adaptive responses

Do Dogs (Canis lupus familiaris) Make Counterproductive Choices Because They Are Sensitive to Human Ostensive Cues?

Dogs appear to be sensitive to human ostensive communicative cues in a variety of situations, however there is still a measure of controversy as to the way in which these cues influence human-dog interactions. There is evidence for instance that dogs can be led into making evaluation errors in a quantity discrimination task, for example losing their preference for a larger food quantity if a human shows a preference for a smaller one, yet there is, so far, no explanation for this phenomenon. Using a modified version of this task, in the current study we investigated whether non-social, social or communicative cues (alone or in combination) cause dogs to go against their preference for the larger food quantity. Results show that dogs' evaluation errors are indeed caused by a social bias, but, somewhat contrary to previous studies, they highlight the potent effect of stimulus enhancement (handling the target) in influencing the dogs' response. A mild influence on the dog's behaviour was found only when different ostensive cues (and no handling of the target) were used in combination, suggesting their cumulative effect. The discussion addresses possible motives for discrepancies with previous studies suggesting that both the intentionality and the directionality of the action may be important in causing dogs' social biases

Marine pollution by hydrocarbures ; study of consequences on Mytilus edulis, with respect to the delay since pollution

Grâce à la collaboration de trois services à l’occasion d’une pollution de la Manche par du fuel n° 2, des analyses de prélèvements de moules, échelonnés sur moins de 2 mois dans deux secteurs pollués, ont permis d’apprécier la teneur encore élevée au 9e jour, en carbures aromatiques et en 3/4 benzopyrène et le retour à une teneur n’excédant pas la teneur d’échantillons témoins, en moins de 42 jours avec régression plus rapide pour le B.T.A.Thanks to the collaboration of three medical departments, with regard to a pollution of the Channel by fuel-oil n° 2, samples of mussels were taken, within less than 2 months in two polluated areas. Their analysis has allowed to determine their still high aromatic carbides and 3/4 benzopyrene content on the 9 th day and the reversion to a content which did not exceed that of the check samples in less than 42 days with a quicker regression as to A.T.B

School level structural and dynamic adjustments to risk promote information transfer and collective evasion in herring

Many large-scale animal groups have the ability to react in a rapid and coordinated manner to environmental perturbations or predators. Information transfer among organisms during such events is thought to confer important antipredator advantages. However, it remains unknown whether individuals in large aggregations can change the structural properties of their collective in response to higher predation risk, and if so whether such adjustments promote responsiveness and information transfer. We examined the role of risk perception on the schooling dynamics and collective evasions of a large herring, Clupea harengus, school (ca. 60 000 fish) during simulated-predator encounters in a sea cage. Using an echosounder, high-resolution imaging sonar and acoustic video analysis, we quantified swimming dynamics, collective reactions and the speed of the propagating waves of evasion induced by a mobile predator model. In the higher risk condition, fish swam faster, exhibited a stronger circular swimming pattern, and we found an increased correlation strength indicating that the school had a greater ability to collectively respond to a perturbation. When exposed to a simulated threat, collective evasions were stronger and behavioural change (evasion manoeuvres) propagated more quickly within the school under environmental conditions perceived as being more risky. Our results demonstrate that large schools make structural and behavioural adjustments in response to perceived risk in a way that improves collective information transfer, and thus responsiveness, during predator attacks.publishe

Examining Complex Vertical Movements of Mesopelagic Scattering Layers: From Taxonomic-Based Migration Decisions to Global Biological Fluxes

Diel vertical migrations (DVM) of mesopelagic animals, which organize in depth-discrete acoustic scattering layers (SLs) linking the surface and deep ocean, represent the largest mass movement of animals on the planet. DVMs are recognized to play a pivotal role in structuring ecological and physicochemical processes in oceanic ecosystems. Mass animal migrations reflect adaptive decisions made by organisms in response to spatiotemporal variations in resources, conferring foraging or reproductive advantages while reducing predation risk. However, there exists little data describing fine-scale behavioral patterns of mesopelagic migrants. Here, we describe the migration patterns of SLs using acoustic data collected in the Gulf of Mexico and examine the characteristics of the migrating layers connecting SLs during DVMs. Our results highlight the complex dynamics of these vertical migrations and reveal that DMVs, during both descending and ascending phases, are comprised of multiple threads differing in speed, length, and taxonomic composition; suggesting that different groups of mesopelagic organisms rely on different adaptive migration strategies. Predictions from an acoustic-based carbon flux model parameterized with DEEPEND catch data indicate that taxonomic categories greatly differ in their contribution to the vertical transport of carbon, with differences reaching several orders of magnitude, implying important biogeochemical consequences. Our study helps to better understand the dynamics of DMVs and their role in trophic interactions, vertical connectivity of food-webs, and Gulf of Mexico biological pump