Black Guillemot vs Common Guillemot

In short

The Black Guillemot and Common Guillemot are both members of the Alcidae family but differ significantly in appearance and behavior. The Black Guillemot is easily recognized by its white wing patches and scarlet legs, while the Common Guillemot lacks these features and has a more uniform dark plumage. Both species are coastal, but the Black Guillemot is more commonly found in inshore waters, whereas the Common Guillemot often frequents open seas.

Identification tips

• Look for white wing patches and scarlet legs to identify Black Guillemots.
• Note the uniform dark plumage of Common Guillemots, lacking white wing patches.
• Observe behavior: Black Guillemots are often solitary or in small groups, while Common Guillemots form large colonies.
• Listen for vocal differences: Black Guillemots whistle, while Common Guillemots have deeper, guttural calls.

Size

The Common Guillemot is generally larger and more robust than the Black Guillemot.

Plumage

The Black Guillemot has distinctive white wing patches and scarlet legs, contrasting with its black body in breeding plumage. In winter, it turns mottled gray and white. The Common Guillemot is dark brown to black with a white underbelly and lacks the white wing patches, maintaining a more uniform appearance year-round.

Behaviour

Black Guillemots are often seen alone or in small groups, diving in shallow, inshore waters. Common Guillemots are more social, often forming large colonies and diving in deeper waters.

Habitat

Black Guillemots prefer inshore waters and are often found near rocky coastlines. Common Guillemots are more likely to be seen in open seas and are associated with large breeding colonies on cliffs.

Voice

Black Guillemots have a high-pitched, whistling call, while Common Guillemots produce a variety of guttural sounds and growls. Vocalizations can be a useful distinguishing feature when both species are present.