The guillemot is a seabird of the auk family that comes on land to breed in the summer. Most guillemots spend their winters out at sea, though some birds are present all year round in inshore waters close to colonies.
Guillemots are slightly larger than razorbills and have a brown head and upper body but a white lower body. The brown colouration can only be distinguished at close quarters and in good light; it often looks black at a distance. The guillemot’s neck, head and long, slender, unmarked black bill merge smoothly when viewed in profile. The tail is shorter than a razorbill’s, leaving the feet protruding when in flight. Guillemots have a distinctive dark line behind the eye and breeding adults also display unmistakable streaked flanks in the wing pits.
The guillemot’s diet consists of a wide variety of fish, as well as crustaceans, marine worms and squid. They forage for food by diving from the sea surface and swimming underwater using their wings for propulsion. Birds can frequently be seen swimming with their heads dipped in water searching for prey. Dives usually last for one to two minutes in which time the birds may cover distances of over 30m.
Guillemots fly with fast wing beats and have a flight speed of 80 km/h. Large groups of birds are often seen flying together in a line just above the sea surface.
- Length 38-46 cm
- Wingspan 61-73
- Weight 490-844 g (male), 561-863 g (female)
Classified in the UK as an Amber List species under the Birds of Conservation Concern 4 (2015 update). Amber listed in Birds of Conservation Concern in Ireland 2014-2019 (2014 update).
Guillemots are susceptible to natural and man-made disasters, with large losses recorded in relation to oil spills and severe storms. However, whilst populations appear to cope and recover from these losses, new threats are posed by the over-exploitation of sand-eels and the predicted increase in stormy weather, both of which can lead to shortages of high energy food for rearing chicks.
Guillemots are common along Scottish coasts especially where there are rocky cliffs, sea stacks and off-shore islands. The main breeding colonies are in the north and west on the islands of Handa, Shetland and Orkney, plus scattered colonies along the East coast. A single pear-shaped egg is laid between mid-April and late May followed by an incubation period of 33-34 days and a period of about three weeks before the chick leaves the nest, still unable to fly.
The Scottish population constitutes 75% of British and Irish populations and approximately 10% of the World population of guillemots. Although population numbers were increasing in Scotland up until the early-1990s, numbers started to fall after the turn of the 21st Century, although this general trend masks regional differences. A decline on the Orkneys, Shetlands and Outer Hebrides was coupled with slight increases along the East and south-east coasts of Scotland.
When to see
mid-April-early August (breeding season)
- The guillemot is the most common auk in the British Isles.
- Guillemots are fiercely territorial, defending what can be tiny nesting areas. They can show aggressive behaviour towards neighbours and the female may reside on the nest site for several weeks after the male takes the chick out to sea in order to protect the nest site from competitors. In some areas, such as the Isle of May, guillemots have been recorded to return to the nest sites as early as October, most probably to defend high-quality nest sites.
- Many North Atlantic and Arctic guillemots may display a variation in their summer plumage, displaying a striking narrow white spectacle around the eye and white line along the furrow behind the eye. This is not a distinct subspecies, but an alternate colouring that becomes more common the farther north the birds breed.