Black Guillemot Vs Guillemot: Key Differences Explained

The Black Guillemot (Cepphus grylle) and the Guillemot (Uria aalge) are both members of the Auk family. Although they share many features they also have enough differences to make differentiating between these two species quite easy.

In this article we’ll take a close look at the differences between these two seabirds allowing you to make a positive identification. Keep reading to find out more.

Table of Contents

Key Takeaways

Guillemots are twice or even three times as large as Black Guillemots
Black Guillemots have a mainly black plumage with bright white wing patches
Guillemots have dark brown or blackish upperparts and white underparts
Black Guillemots have short black bills whereas Guillemots have long, slender black bills
Black Guillemots are mainly solitary birds whereas Guillemots tend to breed in large colonies
Black Guillemots nest in hidden, sheltered locations, often close to the shore
Guillemots nest on narrow, exposed ledges of steep cliffs

What Is The Difference Between A Black Guillemot And A Guillemot?

While both the Black Guillemot and the Common Guillemot share similarities as seabirds within the auk family, they are distinct species with several differences which include;

Visual Differences

In Summer, Black Guillemots have a mainly black plumage with bright white wing patches, in Winter they turn a mottled greyish-white. They have short, black bills and bright red feet.

Guillemots (or Common Murres as they’re known in North America) have dark brown or blackish upperparts and white underparts. They keep this plumage all year round unlike Black Guillemots that have different Winter and Summer plumage.

They have a long, slender black bill and dark red coloured feet which are generally not as bright as those of the Black Guillemot.

Differences In Habitat

Black Guillemots are found in Arctic and North Atlantic coastal regions often near rocky shores and islands. Guillemots prefer more temperate zones across the North Atlantic and North Pacific and tend to breed on cliff ledges in large colonies.

Black Guillemots are more solitary birds and are often spotted alone or in small groups. Guillemots on the other hand, are highly social and form large breeding colonies on cliffs.

Nests & Eggs

There are a number of differences between the nests and eggs of the Black Guillemot and the Guillemot. Black Guillemots nest in hidden, sheltered locations, often close to the shore. They choose crevices in rocks, under boulders, or even inside man-made structures like piers or abandoned buildings.

The nest is typically a simple, unlined depression or a shallow scrape on the ground. Black Guillemots do not build elaborate nests, relying instead on the natural shelter provided by the environment.

The eggs of Black Guillemots are typically off-white to light blue, with dark brown or black speckles or blotches. The speckling provides some camouflage within the rocky environment. They tend to lay 1 or 2 oval eggs each season.

Guillemots nest on narrow, exposed ledges of steep cliffs, often in large, densely packed colonies. These cliffs are typically located along sea coasts.

They also do not build a traditional nest. Instead, the egg is laid directly on the bare rock or soil of the cliff ledge. The egg’s shape and the adult’s body provide stability to prevent it from rolling off.

Guillemot eggs can range from white to shades of green, blue, or brown, often with dark blotches, streaks, or speckles. This variability helps parents identify their own egg among thousands in a crowded colony.

They only lay one pear-shaped egg which is pointed at one end. This unique shape helps prevent the egg from rolling off the cliff ledge by causing it to roll in a tight circle rather than straight off the edge.

Bird Calls

The call of the Black Guillemot is a high-pitched whistle which is particularly noticeable during the breeding season. In Guillemot colonies, you will hear a deep murmuring sound that runs all across the habitat.

This murmuring sound is where the Guillemot gets its North American name from (the Murre).

Size & Weight

The Black Guillemot and the Guillemot differ notably in size and weight, which reflects their adaptations to different environments and lifestyles.

Black Guillemots are around 30 to 32 cm in length with a wingspan of around 52 to 58 cm. They can weigh anywhere between 300 to 460 grams.

Guillemots are far larger birds with an average length of between 38 to 45 cm and wingspan of around 64 to 73 cm. They can weigh anywhere between 850 to 1,130 grams.

Guillemots can weigh as much as 3 times the weight of the Black Guillemot which reflects its larger body size and different ecological adaptations. They also have broader wingspans enabling a more powerful flight.

Frequently Asked Questions

How do the nesting habits of Black Guillemots differ from those of Guillemots?

Black Guillemots nest in hidden, sheltered locations such as crevices in rocks or under boulders, often close to the shore. Their nests are simple, unlined depressions. In contrast, Guillemots nest on narrow, exposed cliff ledges in large colonies and lay their eggs directly on the bare rock, without building a traditional nest.

Which species, Black Guillemots or Guillemots, is larger and heavier?

Guillemots are significantly larger and heavier. They have a length of 38 to 45 cm and a wingspan of 64 to 73 cm, with a weight of 850 to 1,130 grams. In comparison, the Black Guillemot is smaller, with a length of 30 to 32 cm, a wingspan of 52 to 58 cm, and a weight of 300 to 460 grams.

How does the social behaviour of Black Guillemots differ from that of Guillemots during the breeding season?

Black Guillemots are typically more solitary or found in small groups, nesting in secluded spots like crevices or under rocks. In contrast, Guillemots are highly social during the breeding season, forming large, densely packed colonies on cliff ledges, where thousands of birds nest closely together.