Feather pecking in growers: a study with individually marked birds.

1. The aim of the present study was to investigate whether individual birds specialise in feather pecking. Growers were individually marked and reared in groups of 30 or 31 in pens with a slatted floor. At an age of 4 to 6 weeks feather pecking was frequent in all pens. 2. On average 83% of all group members (10 groups, experiment 1) were recorded at least once as initiator of a feather pecking interaction. In each group 2 to 6 individuals feather pecked more than twice as often as the average for the group, and were defined as 'high rate peckers'. They initiated 39% of all recorded feather pecking interactions. 3. Every interaction was classified (with increasing intensity) as pecking, pinching, pulling or plucking. Compared to the others, 'high rate peckers' had more of their feather pecking classified as plucking and less classified as pecking. 4. There was no evidence that particular individuals specialised in pecking at other specific birds, at specific areas of the body or at birds engaged in specific activities. 5. Growers (3 groups, experiment 2) that had just feather pecked engaged in more feather pecking during a subsequent 2-min focal observation than control birds that had not pecked before the start of the observation. 6. It was concluded that feather pecking interactions are clustered in time and that the behaviour is not performed by just a few members of a group. However, some individuals are characterised by relatively high rates and more severe forms of feather pecking.