Guillemots gather in breeding colonies for the summer. Between May and July, females lay a single egg directly onto cliff ledges; its conical shape prevents it from rolling off (4). At around three weeks of age, the young guillemot leaves the colony before it has fledged, and dramatically plunges into the sea accompanied by the adult male (6), who will care for the young at sea until it becomes independent a couple of months later (2), (7). Shortly after leaving the breeding colonies between June and August, adult guillemots undergo the main annual moult, and become flightless for around six to seven weeks (7).
During the winter guillemots disperse fairly widely, with young birds covering the greatest distances (7). Throughout the year, the diet consists mainly of various small species of fish, as well as crustaceans, marine worms and molluscs. Sand eels are particularly important during summer (2). Guillemots dive to obtain food (2), 'flying' under water with their wings (6).