Gregarious nesting—An anti-predator response in laying hens

Abstract

Gregarious nesting can be defined as a behaviour that occurs when a laying hen (Gallus gallus domesticus) given the choice between an occupied and an unoccupied nest site chooses the occupied nest site. It occurs frequently in flocks of laying hens kept under commercial conditions, contrasting the behaviour displayed by feral hens that isolate themselves from the flock during nesting activities. What motivates laying hens to perform gregarious nesting is unknown. One possibility is that gregarious nesting is an anti-predator response to the risk of nest predation emerging from behavioural flexibility in nesting strategy. The aim of the present experiment was to investigate whether gregarious nesting due to behavioural flexibility in nesting strategy is an anti-predator response. Twelve groups of 14–15 Isa Warren hens age 44 weeks were housed in pens each containing three adjacent roll-out nest boxes. Nesting and spacing behaviour were video recorded for 5 days in each of three distinct periods; (a) pre-predator; a pre-exposure period, (b) predator; a period with daily exposure to a simulated attack by a lifelike flying model of a hooded crow (Corvus cornix, a potential egg-predator), and (c) post-predator; a post-exposure period. Additional data collected were the behaviour of each hen 5min prior to and 10s after the simulated predator attacks. The hens reacted with fear-related behaviour to the simulated predator attacks, e.g. the number of hens engaged in normal non-agitated behaviour decreased from before to after exposure to the predator model (P<0.001), and this did not change with day of exposure (P>0.05). The proportion of gregarious nest box visits of the total number of visits, where the hens had a choice between gregarious or solitary nesting, was found to be higher during the predator period (P<0.01). The general distribution of hens in the pens did not change between periods (P>0.05). In conclusion, evidence was found for the proposed hypothesis that gregarious nesting is an anti-predator response.