Gannets feed on pelagic shoaling fish, such as mackerel and herring (6), and when fishing, often execute breathtaking plunge-dives from considerable heights, splashing into the sea with the wings folded back (2). The breeding colonies, known as gannetries, are occupied from March to September (8). The nests are tightly packed together, and roaming chicks or adults who land in the wrong location are often fiercely attacked (9). Courtship involves ritualised preening, bowing and head-pointing (9), and nesting commences in April (9). The mound nest consists of seaweed, feathers and plant material, and extra seaweed may be incorporated into the nest during incubation of the pale blue, chalky egg (7), which is laid in late April or May (9). A clutch typically consists of just one egg, although two may occasionally be produced. Incubation takes between 43 and 45 days (7), and is carried out by both parents, by placing their feet on the egg (9). After fledging, most juveniles migrate to the south during August and September (6); they do not attain full adult plumage until 5 years of age (6).