Systematic ringing and subsequent resighting of 6 annual cohorts of yo
ung Guillemots indicated a high degree (42%) of philopatry to the nata
l group of 50-200 pairs. However, few young bred close to the sites wh
ere they were reared. There was no statistically significant sex diffe
rence. There seems little prospect that adjacent individuals, or even
those breeding on a single ledge, are closely related.