Nest location selection in laying hens

Part one will be a descriptive study of nest sharing and crowding. The first experiment is designed to investigate if nest sharing occurs in hens kept under semi-natural conditions. The second experiment aims at describing crowding and investigating the welfare consequences of crowding such as pacing and increased aggression.

During the second part of the project, the motivation to select a nest already occupied by another hen or egg will be investigated. The results from part one will reveal if crowding occurs more often in some nest boxes than in others, but not why this happens. There are only 2 possible explanations to the cause of crowding. One is that the hens possess a preference for the same nest box characteristics. The other explanation is that the presence of another hen carrying out nesting behaviour may motivate other hens to join her in the activity. However, this leads to another question; why is the presence of another hen a motivating factor? One possibility is that it is due to an inability to distinguish between nests, another that it is an anti-predator strategy. The secretive nesting behaviour that a feral hen displays is an anti-predator response that minimizes the risk of having the nest detected by predators. The commercial laying hen does not have the possibility of isolating herself from the flock. Instead she may chose the alternative anti-predator response; laying her egg in a nest already occupied by other hens, i.e. crowding. This strategy generates a dilution effect as a hen’s egg will just be one of many in the nest, i.e. the risk of having her egg predated is reduced by the presence of other eggs (Krebs & Davies 1993).

The aim of the third part of the project is to test if it is possible to reduce or prevent crowding in nest boxes using the knowledge gained in part one and two.