SPACING BEHAVIOR AND AN ETHOLOGICAL APPROACH TO ASSESSING OPTIMUM SPACE ALLOCATIONS FOR GROUPS OF LAYING HENS

This paper tackles the problem of assessing spatial requirements for laying hens housed commercially. Some of the approaches taken previously to determine space allocations are presented briefly and a practical method to determine a compromise pen size is proposed based on comparisons of observed and expected interbird distances. The benefits and limitations of this method are discussed. The main part of the paper discusses the ultimate and proximate factors influencing spatial requirements. In keeping with studies in behavioural ecology, risk of predation and the probability of finding food and other resources, in combination with competition between individuals for these resources, are thought to be the main ultimate factors influencing spacing behaviour. Position in the dominance hierarchy, and especially behavioural activity, are thought to be the main proximate factors. It is proposed that these various ultimate and proximate factors can be simplified into those that tend to bring individuals together and those that tend to keep them apart. The distance between two individuals at any one moment in time is therefore the distance at which these opposing tendencies are balanced. Such an hypothesis allows a stochastic model to be presented leading to predictions of the movements of animals towards and away from each other. Some experiments are presented confirming that birds do move as predicted from this stochastic model, and possible ways by which this could be used in the future to assess spatial requirements for laying hens are discussed. A consequence of accepting this view and acknowledging that many ever-changing factors influence spatial requirements must be the realisation that there will be no single figure for how much space laying hens should be given. At best only a range can be proposed. Nevertheless, the opinion is put forward that spacing behaviour is such an integral part of the social behaviour of animals that research in this area is, in itself, a valuable contribution. It is further suggested that, when any behavioural observations are carried out in a social context, more consideration should be given to how the spatial requirements of the experimental animals may be influencing their behaviour.