Behavioural responses of commercially farmed laying hens to humans: evidence of stimulus generalization

Abstract

The behavioural responses of birds to experimenters varying in a number of attributes, such as sex, height, clothing and the wearing of spectacles, were determined in a series of five experiments. A total of 320 birds aged between 50 and 57 weeks of age and housed in single-hen cages at a large commercial farm were used. The hens' responses were observed in a standardized test in which their position, orientation and posture were recorded when a stationary human stood 60 cm from the front of the cage. The hens' responses to humans were unaffected by variations in the majority of human attributes tested, including sex, height and the presence of spectacles. Only one of the eight variables measured appeared to be sensitive to the type of clothing; more crouch or escape postures, indicative of greater fear, were seen when the experimenter wore overalls (to which the birds were less accustomed), rather than street clothes. Collectively, the results demonstrate that stimulus generalization across a wide range of human attributes can occur at commercial farms, or at least those at which the hens have had previous experience of a number of humans.