Social Feeding in Birds

Abstract

1. Feeding and non-feeding chaffinches and sparrows are attractive to members of their own species. Non-feeding chaffinches are less attractive, and this is probably also true for sparrows. Approach responses can be elicited by another bird's feeding behaviour, and morphology and/or behaviour other than feeding. 2. Feeding and non-feeding sparrows and chaffinches are reciprocally attractive. Chaffinches are more attracted by feeding than non-feeding sparrows, but this does not obviously apply to sparrows observing chaffinches. 3. Adult and juvenile reactors will tend to feed on familiar food if they see actors of the same species feeding (Social facilitation). The tendency is stronger if the actor's and reactor's foods are close together (Local enhancement). This particularly applies to juveniles. 4. Reactor chaffinches and sparrows, both adults and juveniles, give the impression of copying the feeding habits of actors, and will eat similar, but in other circumstances unacceptable, food of aposematic appearance. Reactors will similarly feed from strange microhabitats if they observe actors doing so. 5. Juveniles were less wary and sampled the strange foods and fed from strange food receptacles very much more readily. Very young chicks were even more explorative, and were seen to peck at a very wide range of different objects. 6. Juvenile chaffinches and sparrows could thus be caused to peck at unusual objects, and from strange microhabitats, solely by social facilitative effects. This was particularly so if there was a strong directional component. 7. Sparrows, and probably chaffinches, show a type of behaviour that has been described as the transfer of a searching image. 8. Interspecific social feeding was demonstrated between actor chaffinches and reactor sparrows. The responses of the sparrows were on the whole weaker than those directed towards their own species. 9. Very young naive chicks pecked particularly at moving objects that were in juxtaposition with sharp points. 10. Very young chicks were powerfully influenced by a mechanical, pecking hen, and compared with control chicks with a non-moving hen, a. approached it more readily, b. took more pecks in its presence, c. aimed more pecks near the hen, d. had a lower food latency, and e. aimed more correct pecks at food resembling that being pecked at by the hen. 11. After socialisation, 30 hour chicks delivered more pecks than isolate control birds. 12. 7 and 21 day old socialised chicks reversed the tendencies shown in the 30 hour group, and in the presence of a mechanical pecking hen they pecked less, had larger hen approach latencies, and larger food latencies than control isolates of the same age. 13. The development of social feeding is discussed, and it is suggested that the social facilitation could have developed from the normal innate response to a moving object, (viz. an approach followed by pecking in the moving object's vicinity) which has been conditioned specifically to a pecking bird as opposed to the innate approach response to a generalised moving object. The separation of the pecking response from the approach response, which has been demonstrated in the adult chaffinches and sparrows, could also be accomplished by conditioning. Thus the phenomenon described as local enhancement is probably social facilitation with a directional component and has been derived from the initial innate approach to moving objects generally. 14. The importance of social feeding is discussed in relation to the predator/prey relationships, the impact of social feeding upon cryptic and aposematic prey, and the selection and location of a balanced diet. It is suggested that all these relationships may be profoundly affected by the highly developed social feeding that occurs in chaffinches and sparrow. Other species have not been investigated so fully but observations on crows seemed to indicate that they probably have well developed social feeding behaviour, and L. TINBERGEN reports similarly upon tits.