Timothy J. Roper

Group decision-making in animals

Groups of animals often need to make communal decisions, for example about which activities to perform, when to perform them and which direction to travel in; however, little is known about how they do so. Here, we model the fitness consequences of two possible decision-making mechanisms: ‘despotism’ and ‘democracy’. We show that under most conditions, the costs to subordinate group members, and to the group as a whole, are considerably higher for despotic than for democratic decisions. Even when the despot is the most experienced group member, it only pays other members to accept its decision when group size is small and the difference in information is large. Democratic decisions are more beneficial primarily because they tend to produce less extreme decisions, rather than because each individual has an influence on the decision per se. Our model suggests that democracy should be widespread and makes quantitative, testable predictions about group decision-making in non-humans.

Reliable microsatellite genotyping of the Eurasian badger ( Meles meles ) using faecal DNA

The potential link between badgers and bovine tuberculosis has made it vital to develop accurate techniques to census badgers. Here we investigate the potential of using genetic profiles obtained from faecal DNA as a basis for population size estimation. After trialling several methods we obtained a high amplification success rate (89%) by storing faeces in 70% ethanol and using the guanidine thiocyanate/silica method for extraction. Using 70% ethanol as a storage agent had the advantage of it being an antiseptic. In order to obtain reliable genotypes with fewer amplification reactions than the standard multiple‐tubes approach, we devised a comparative approach in which genetic profiles were compared and replication directed at similar, but not identical, genotypes. This modified method achieved a reduction in polymerase chain reactions comparable with the maximum‐likelihood model when just using reliability criteria, and was slightly better when using reliability criteria with the additional proviso that alleles must be observed twice to be considered reliable. Our comparative approach would be best suited for studies that include multiple faeces from each individual. We utilized our approach in a well‐studied population of badgers from which individuals had been sampled and reliable genotypes obtained. In a study of 53 faeces sampled from three social groups over 10 days, we found that direct enumeration could not be used to estimate population size, but that the application of mark–recapture models has the potential to provide more accurate results.

Activity synchrony and social cohesion: a fission-fusion model

A social group can only be spatially coherent if its members synchronize activities such as foraging and resting. However, activity synchronization is costly to individuals if it requires them to postpone an activity that would be personally more profitable in order to do what the rest of the group is doing. Such costs will be particularly high in groups whose members belong to different age, size or sex classes since the optimal allocation of time to various activities is likely to differ between such classes. Thus, differences in the costs of activity synchronization between and within classes could cause non–homogenous groups to be less stable than homogenous groups, with the result that homogenous groups predominate in the population: that is, they could cause ‘social segregation’ of animals of different sex, size or age. We develop a model that predicts the degree of social segregation attributable to differences in activity synchronization between homogenous and non–homogenous groups and use this model in determining whether activity synchronization can explain intersexual social segregation in red deer (Cervus elaphus). Differences in activity synchronization between mixed–sex and unisex groups of red deer explained 35% of the observed degree of intersexual social segregation, showing that activity synchronization is an important cause of social segregation in this species.

“Leading According to Need” in Self‐Organizing Groups

Self‐organizing‐system approaches have shed significant light on the mechanisms underlying synchronized movements by large groups of animals, such as shoals of fish, flocks of birds, or herds of ungulates. However, these approaches rarely consider conflicts of interest between group members, although there is reason to suppose that such conflicts are commonplace. Here, we demonstrate that, where conflicts exist, individual members of self‐organizing groups can, in principle, increase their influence on group movement destination by strategically changing simple behavioral parameters (namely, movement speed, assertiveness, and social attraction range). However, they do so at the expense of an increased risk of group fragmentation and a decrease in movement efficiency. We argue that the resulting trade‐offs faced by each group member render it likely that group movements are led by those members for which reaching a particular destination is most crucial or group cohesion is least important. We term this phenomenon leading according to “need” or “social indifference,” respectively. Both kinds of leading can occur in the absence of knowledge of or communication about the needs of other group members and without the assumption of altruistic cooperation. We discuss our findings in the light of observations on fish and other vertebrates.

Responses of Wild Birds to Novel Prey: Evidence of Dietary Conservatism

Models of the evolution of aposematic coloration assume that the first brightly coloured morphs to appear in a cryptic population of chemically defended insects would have attracted the attention of predators, putting them at a disadvantage by comparison with their less conspicuous relatives. However, if birds show a generalised avoidance response (neophobia) towards novel prey, this could allow conspicuous morphs to survive long enough to enable aposematic selection to take over. The present experiment attempted to evaluate this possibility by pre-training individually identifiable wild blackbirds (n=19) and robins (n=12) with pastry baits of a particular colour and then giving them a choice between familiar-coloured and novel-coloured baits. The number of trials taken for each bird to contact the novel colour of bait for the first time, and toeat it on a regular basis, was recorded. Birds were extremely variable in their responses: some accepted novel-coloured baits immediately while others took more than a hundred exposures before eating them regularly. Green baits were avoided for longer than red or yellow. The results suggest (a) that a new aposematically coloured morph would not necessarily suffer a higher predation rate than its cryptic ancestors, and (b) that colours that are normally considered to be aposematic on the basis of laboratory experiments may not be especially aversive to wild birds.

Olfaction in the domestic fowl: a critical review.

It has been known for some time that many species of birds, including domestic fowl Gallus domesticus, have an olfactory sense. However, the functional significance of avian olfaction is less clear. We review neurobiological, embryological and behavioral evidence relevant to the question of how domestic fowl use the sense of smell. Evidence suggests a potential role for olfaction in the formation of attachments to familiar objects or environments; in the elicitation of fear responses by alarm and predator-related odors; in the control of feeding and drinking; and in avoidance of noxious substances. The fact that domestic fowl can detect and respond to a wide range of odors, in a variety of behavioral contexts, has important practical implications, especially in relation to welfare and husbandry.

Effects of novel colour and smell on the response of naive chicks towards food and water

Many warningly coloured prey emit a conspicuous smell of pyrazines when attacked by a predator and it has been suggested that this odour cue constitutes part of the preys aposematic anti-predator defences. The aim of the study was to test the hypothesis that pyrazine odours enhance the neophobic response of birds towards prey that is novel in appearance. Naive domestic chicks,Gallus gallus domesticus, were presented with food or water that was either familiar or novel (coloured with food dye) in appearance, in the presence or absence of five different odours. The odours in question were 2-methoxy-3-sec-butyl pyrazine, 2-methoxy-3-isobutyl pyrazine, almond oil, vanilla oil and thiazole. Presence of each of the pyrazines and of almond odour increased the latency with which chicks ate or drank, but only when the food or water was a novel colour. The effect was weaker with vanilla odour and absent with thiazole. When odours of 2-methoxy-3-sec-butyl pyrazine and thiazole were paired with a novel-coloured environment, eating and drinking were not inhibited. This suggests that odours naturally associated with chemical defence in insects or plants do enhance neophobia, but only when presented in conjunction with prey that has a novel appearance. However, confounding factors such as differences in odour intensity cannot at present be excluded. The implications of the results for theories concerning the evolution of warning coloration are discussed.

Social transmission of food-preferences in adult rats

Abstract Three experiments were carried out to investigate the social transmission of food-related information in adult rats. Experiment 1 showed that when one member of a group of rats (the ‘leader rat’) was exposed to a novel artificially-flavoured food, a preference for that food developed in other members of the group (‘follower rats’), despite the fact that they themselves had not had direct access to the food source. Experiment 2 showed that development of a preference in follower rats was only partly abolished by washing the leader rat after it had been exposed to the novel food. In addition, a preference developed in follower rats if a novel food odour was presented on a cotton swab in the home cage, or if the odour was painted onto the body of the leader rat. Experiment 3 showed that when the leader rat was allowed to eat food bearing one odour, while a different odour was presented in the home cage, follower rats subsequently showed enhanced consumption of foods bearing both odours. We conclude that the behaviour of rats towards a new food source can be influenced (a) by particles of food adhering to a conspecifics pelage; (b) by food odours transmitted by a conspecific in some other way, such as through the faeces; and (c) by simple exposure to a novel odour not directly associated with food. The most likely mechanism underlying these effects is that experience of an odour reduces the rats neophobia towards any object (including food) contaminated with that odour.

Democracy in animals: the evolution of shared group decisions

A ‘consensus decision’ is when the members of a group choose, collectively, between mutually exclusive actions. In humans, consensus decisions are often made democratically or in an ‘equally shared’ manner, i.e. all group members contribute to the decision. Biologists are only now realizing that shared consensus decisions also occur in social animals (other than eusocial insects). Sharing of decisions is, in principle, more profitable for groups than accepting the ‘unshared’ decision of a single dominant member. However, this is not true for all individual group members, posing a question as to how shared decision making could evolve. Here, we use a game theory model to show that sharing of decisions can evolve under a wide range of circumstances but especially in the following ones: when groups are heterogeneous in composition; when alternative decision outcomes differ in potential costs and these costs are large; when grouping benefits are marginal; or when groups are close to, or above, optimal size. Since these conditions are common in nature, it is easy to see how mechanisms for shared decision making could have arisen in a wide range of species, including early human ancestors.

Foray search: an effective systematic dispersal strategy in fragmented landscapes.

In the absence of evidence to the contrary, population models generally assume that the dispersal trajectories of animals are random, but systematic dispersal could be more efficient at detecting new habitat and may therefore constitute a more realistic assumption. Here, we investigate, by means of simulations, the properties of a potentially widespread systematic dispersal strategy termed “foray search.” Foray search was more efficient in detecting suitable habitat than was random dispersal in most landscapes and was less subject to energetic constraints. However, it also resulted in considerably shorter net dispersed distances and higher mortality per net dispersed distance than did random dispersal, and it would therefore be likely to lead to lower dispersal rates toward the margins of population networks. Consequently, the use of foray search by dispersers could crucially affect the extinction‐colonization balance of metapopulations and the evolution of dispersal rates. We conclude that population models need to take the dispersal trajectories of individuals into account in order to make reliable predictions.