Biomedical subjects

CS Evans

Publications and source records attributed to CS Evans.

3 recordsLinked to original sources

PubMed1999

Chicken food calls are functionally referential.

Male chickens, Gallus gallus domesticus, usually produce characteristic 'food' calls upon discovering edible objects, and are more likely to do so in the presence of a hen. Food calling is thus dependent upon food and modulated by social context, which is consistent with the idea that hens respond because they anticipate a feeding opportunity. An alternative model suggests that female behaviour is not mediated by the predicted presence of food but rather by social information, such as a low probability of male aggression. We conducted two playback experiments to explore the type of information encoded in food-associated vocal signals. Isolated hens were played recorded food calls and we compared their responses with those evoked by ground alarm calls (which have similar acoustic characteristics) and by contact calls (which are produced under similar social circumstances). Hens responded to food call playbacks by fixating downwards with the frontal binocular field. This anticipatory feeding movement was specific to food calls and did not occur in either of the control conditions. Food calls also affected looking downwards selectively. There were no differences between the call types in their effects on social behaviour, such as approach and contact calling, nor were there differences in the nonspecific effects of sound playback, such as orienting towards the loudspeaker or increased locomotor activity. Chicken food calls appear to provide conspecifics with information about the presence of food. This property has not hitherto been demonstrated in any natural system of animal acoustic signals. Copyright 1999 The Association for the Study of Animal Behaviour.

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PubMed1999

An experimental study of behavioural group size effects in tammar wallabies, Macropus eugenii.

As animals aggregate with others, the time they allot to social and nonsocial activities changes. Antipredator models of vigilance and foraging group size effects both predict a nonlinear relationship between group size and the time allocated to behaviour. Group size effects were experimentally studied in captive adult female tammar wallabies, a small macropodid marsupial, by increasing group size from 1 to 10. Tammars foraged more, looked less, groomed more, engaged in more aggressive interactions and moved about less as group size increased. Nonlinear regression models explained more variation in the time allocated to foraging, looking, locomotion and affiliative behaviour than linear models. Variation in self-grooming and aggression was better explained by linear models. Wallabies lay down significantly more, and walked significantly less, as group size increased: these relationships were significantly nonlinear. Thus, changes in perceived predation risk, which are characterized by nonlinear relationships, explain tammar wallaby group size effects for most activities. These results support the assertion that predation has played an important role in macropodid social evolution. Moreover, the findings suggest that conservation biologists should pay particular attention to group size when translocating or reintroducing endangered macropodids. Copyright 1999 The Association for the Study of Animal Behaviour.

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PubMed1999

Use of electroreception during foraging by the Australian lungfish.

A diverse range of animals, including elasmobranchs and nonteleost fish, use passive electroreception to locate hidden prey. The Australian lungfish, Neoceratodus forsteri (Krefft 1870), has ampullary organs analogous in form to the electroreceptors of other nonteleost fish. Afferents from these ampullae project to regions in the brain that are known to process electrosensory information in other species, suggesting that N. forsteri possesses an electric sense that may be used during prey location. To explore this hypothesis directly, we first characterized food-locating behaviour in N. forsteri and then conducted an experiment designed to quantify the effects of manipulating electrical and olfactory stimuli from live prey. A small crayfish, Cherax destructor, was housed in a specially constructed chamber hidden beneath the substrate, which prevented emission of chemical, mechanical and visual cues, but allowed transmission of bioelectric fields. Control treatments included presentation of electrically shielded prey, a dead crayfish and an empty chamber. In some treatments, a competing olfactory signal was presented simultaneously at the other end of the test tank to assess the relative salience of this sensory modality. The lungfish responded to the crayfish in the unshielded chamber with accurate and sustained feeding movements, even with a competing olfactory signal. By contrast, the abolition of electrical cues in the three control treatments reduced the accuracy and frequency of feeding movements in the vicinity of the target chamber. These results show that N. forsteri is capable of perceiving the weak electric fields surrounding living animals, and suggest that it uses this information when foraging to locate prey hidden from view. Copyright 1999 The Association for the Study of Animal Behaviour.

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