The assessment of fear in domestic hens exposed to a looming human stimulus

Abstract

The behavioural and physiological responses of hens exposed to a slowly approaching human being were assessed using remote observation and radio telemetry of heart rate. Forty isolated hens of two strains and from two rearing environments were used. The sequence of behavioural changes included looking around, ceasing feeding, head shaking or complete withdrawal and finally crouching or escape behaviour. The heart rate rose from a mean level of 303 beats/min when the birds were at rest, to 465 beats/min when the cage was opened and the bird caught and held at the conclusion of the approach. The light hybrid strain showed more pronounced behavioural responses and a greater proportional rise in heart rate in the course of the approach than the medium hybrid birds, consistent with the induction of a higher level of fear. An environmental effect was also observed, pen-reared birds were more disturbed than caged ones. The similarity of the time course of the physiological and behavioural measures supports the concept of fear as an intervening variable which has simultaneous effects on heart rate and behaviour. Both may be effective in assessing fear, and they should be regarded as complementary rather than alternative measures.