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Pays, O.; Sirot, E.; Fritz, H. |
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Title |
Collective Vigilance in the Greater Kudu: Towards a Better Understanding of Synchronization Patterns |
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Year |
2011 |
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Ethology |
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Collective detection of predators is one of the main advantages of living in groups in prey species. However, the mechanisms linking individual and collective vigilance remain largely unknown. Here, we investigated individual and collective vigilance in a natural population of greater kudu (Tragelaphus strepsiceros), a gregarious ruminant living under high predation risk. Controlling for environmental, individual and group factors, we show that the proportion of time during which at least one individual was vigilant increased with group size, whereas individual investment in vigilance decreased. We also show that individuals tended to synchronize both vigilance and feeding activities. More generally, and whatever the considered group size, we demonstrate how the independent scanning assumption underestimated both the proportion of time during which no individual was vigilant and the proportion of time during which all individuals were simultaneously vigilant, but overestimated the proportion of time during which one vigilant individual only was present. Our results thus contrast with the point of view that the alternative to independent vigilance is coordinated vigilance and plead for a better description of the processes whereby reciprocal influences between individuals shape collective patterns of vigilance. |
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Blackwell Publishing Ltd |
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1439-0310 |
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Equine Behaviour @ team @ |
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5425 |
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Author |
Poisbleau, M.; Fritz, H.; Valeix, M.; Perroi, P.-Y.; Dalloyau, S.; Lambrechts, M.M. |
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Title |
Social dominance correlates and family status in wintering dark-bellied brent geese, Branta bernicla bernicla |
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Journal Article |
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Year |
2006 |
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Animal Behaviour. |
Abbreviated Journal |
Anim. Behav. |
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71 |
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6 |
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1351-1358 |
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In many gregarious species, including ducks and geese, being dominant provides more benefits than costs, because dominants have better access to resources essential for survival or reproduction. In geese, being in better body condition during migration towards the breeding grounds positively influences reproductive success. However, underlying proximate mechanisms linking prebreeding body condition on the wintering grounds to breeding success remain poorly understood. We investigated social dominance correlates and family status, in three consecutive winters, in a free-ranging, migrating, dark-bellied brent goose population. Families with juveniles dominated pairs, and pairs dominated singletons. Dominance rank did not increase with the number of juveniles per family. Males were dominant over females. Social dominance and reproductive status for a given winter were significantly correlated with body mass, body size and body condition during the previous winter, suggesting that body condition in winter also affects subsequent breeding success and hence also dominance. Levels of testosterone and triiodothyronine were not correlated with immediate or later dominance or reproductive status. We discuss the role of family status as a signal of social status in determining reproductive strategies. |
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0003-3472 |
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Equine Behaviour @ team @ |
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4690 |
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Fleurance, G.; Duncan, P.; Fritz, H.; Cabaret, J.; Cortet, J.; Gordon, I.J. |
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Title |
Selection of feeding sites by horses at pasture: Testing the anti-parasite theory |
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Journal Article |
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Year |
2007 |
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Applied Animal Behaviour Science |
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Appl. Anim. Behav. Sci. |
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108 |
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3-4 |
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228-301 |
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Foraging strategies; Horses; Parasite risk; Patch choice |
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Management of grazed grasslands for production and/or conservation objectives requires a thorough understanding of the choices of feeding sites by herbivores, and of the biological processes involved. Most models of the feeding strategies of herbivores are based on the principle that optimising the intake of energy (or some nutrient) is the primary goal of foragers but other selective forces, such as parasitism, could be important. Gastrointestinal parasites (including cyathostome nematodes) have powerful effects on the fitness of herbivores and may act as a major selection pressure favouring host behaviour that reduces the risk of encountering parasites. Among large herbivores, horses have perhaps the most marked tendency to select particular feeding sites within grasslands. We test here: (1) whether horses select feeding patches with relatively low parasite densities and (2) if their choice is affected by their parasite load. We used 10 two-year old saddle-horses and three periods. In the first period, the horses were under natural parasitism which varied strongly among individuals; in the second period they were all dewormed, and in the third, a sub-set of the horses was experimentally infected with cyathostome larvae. Ninety-eight percent of the infective larvae in the pasture were found <1 m from faeces. The main determinant of the choice of feeding patch by horses was the availability of patches of different parasite risk and grass height. Controlling for availability, the horses used tall grasses (>16 cm) less than expected, whether the grass was contaminated or not, and they selected for short patches >1 m from faeces, where the risk of encountering parasites was low. These results suggest that selection of feeding sites by horses is driven by an interaction between their nutritional and anti-parasite strategies: the horses avoid the patches of tall grass which are generally of low quality and areas contaminated by parasite larvae which leads them to prefer the patches of short grass far from faeces. The parasite status of the horses at the time of the experiment had no effect on their feeding choices. However, before concluding that the challenge by cyathostomes has no effect on the selection of feeding sites in horses, it will be necessary to test whether the history of parasitism of the individuals, rather than the current status, is important. |
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Equine Behaviour @ team @ |
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4228 |
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Monard, A.-M.; Duncan, P.; Fritz, H.; Feh, C. |
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Title |
Variations in the birth sex ratio and neonatal mortality in a natural herd of horses |
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1997 |
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Behavioral Ecology and Sociobiology |
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Behav. Ecol. Sociobiol. |
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41 |
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4 |
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243-249 |
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Variations in birth sex ratios and sex differences in juvenile mortality occur in a number of mammalian species, and in many cases have been linked to resource availability. Most of these biases in offspring sex ratios concern polygynous species with pronounced sexual dimorphism, and where females only are philopatric. Data on species with unusual life-history strategies, such as slight sexual dimorphism or dispersal by both sexes, are of particular interest. In this study of a natural herd of horses (Equus caballus) which experienced an eruptive cycle, and therefore a period of nutritional stress, male offspring had higher neonatal mortality rates in nutritionally poor years than in good ones, whereas “year quality” had no effect on the mortality of female offspring; year quality could therefore be used by mares as predictor of sex-specific offspring survival. We show that the environmental conditions that predicted lower survival of males were negatively related to their production: the birth sex ratio the following year was female-biased; and mares were less likely to produce a son when they had produced a son the preceding year. There was no significant effect of mother's parity, age or rank, or the timing of conception or birth on offspring sex ratios. The mechanism leading to biases in the birth sex ratio could have been the loss of male embryos by mares that did not foal. As there was no evidence for selective abortion of male foetuses in females that did foal the next year, it is not necessary to invoke maternal adjustment, though this remains a possibility. Finally, there was a suggestion that male offspring were more costly to raise than females, since mothers that reared a son in poor years tended to experience an increase in the interbirth interval between their two subsequent offspring. |
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Equine Behaviour @ team @ |
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2388 |
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Poisbleau, M.; Jenouvrier, S.; Fritz, H. |
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Title |
Assessing the reliability of dominance scores for assigning individual ranks in a hierarchy |
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2006 |
Publication |
Animal Behaviour. |
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Anim. Behav. |
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72 |
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4 |
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835-842 |
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The dominance score (number of wins divided by the total number of interactions) is the most widely used procedure in field studies to rank individuals. Its reliability depends on the number of interactions on which it is calculated. However, most authors use it without any estimate of the associated error. We describe the precision associated with a dominance score estimate as a function of the number of interactions on which it is based, and hence provide a tool to plan field protocols and effort. The precision error decreases according to a power function with increasing number of interactions, but with more precision for extreme scores for any given number of interactions. We discuss the fact that the minimum number of interactions should be based on the precision associated with the 50% score, the least precise of all scores. We also emphasize the trade-off between recording effort and precision of the estimator, and give an example of our choice of 26 interactions for fieldwork on ducks and geese. When comparing individual ranks based on dominance scores with ranks given by the dominance matrix, we found a good correlation, with more mismatches around the middle of the hierarchy. This was consistent with the precision calculated with our model. We conclude that dominance score is a reliable tool, but conclusions must take into account the number of interactions on which the calculations are done. We also discuss the importance of initial assumptions and sources of bias in field studies. |
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refbase @ user @ |
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456 |
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