THE BREEDING BIOLOGY OF THE GANNET SULA BASSANA ON THE BASS ROCK, SCOTLAND

SUMMARY The Bass colony is increasing—in 1962 there were 5,350–5,700 breeding pairs; 1,340–1,430 pairs of non‐breeders with nests or sites (mainly pairs in their season before first breeding) and 2,000–2,500 “club” birds without nest or site. 15% of nests were occupied by both birds of a pair at the time of the count. Oldest males return to the colony in January, followed by experienced females, considerably later by young adult‐plumaged birds,...