Black Guillemot Diet and Size: Feeding Habits, Predators, and Measurements

Black Guillemots are resident birds in the UK and can be seen off the coasts and around the sea lochs of western Scotland and the northern and western isles as well as in Ireland, the Isle of Man and other selected locations in England and Wales.

Black Guillemots are easily identifiable in their summer plumage which is all black except for bright white patches on each wing. They have black bills and bright red legs and feet and the inside of their mouths are bright red as well.

They lose their breeding plumage in the autumn and adopt white underparts and pale grey upperparts with barred light grey and white patterning.

In this article we’ll take a close look at the dietary habits, breeding habits as well as the size and weight of these fascinating seabirds and much more besides. Keep reading for more information.

Table of Contents

The Dietary Habits Of The Black Guillemot

As Black Guillemots spend most of their lives in the water, they have a typically aquatic diet. They are well known for their diving skills and are able to dive an impressive 164 feet (50 metres) underwater and remain there for around 2 minutes or more whilst hunting for food.

What Does A Black Guillemot Eat?

Their diet consists primarily of small fish and marine invertebrates, which they catch through diving. They typically forage close to shore, often diving to the seafloor to capture prey such as sculpins, cod, blennies, and various crustaceans like shrimps and crabs.

Their diet can vary based on location and availability, but fish are generally the main component.

What To Feed A Baby Black Guillemot?

When feeding their chicks, Black Guillemots predominantly bring back small fish, which are easier for the chicks to swallow and provide the necessary nutrients for growth. Parents often carry one fish at a time in their beaks back to the nest and may feed their chicks multiple times a day.

The choice of prey is typically driven by what is abundant and accessible close to their nesting sites.

Breeding Habits Of Black Guillemots

Black Guillemots have distinctive breeding habits and courtship rituals, reflecting their life in harsh, often remote environments. Their breeding season usually starts in late spring or early summer depending on where they live. In northern areas they might start breeding later due to colder conditions.

During courtship, pairs engage in mutual displays where they bob their heads and call to each other. This ritual helps to strengthen the bond between the pair. They also practise a ritual known as “nosing” which is where the birds touch bills.

Males may perform aerial displays, flying in a pattern or around the nesting site to attract the female’s attention. They also display their bright red legs during these displays, which is a key visual signal.

Do Black Guillemots Mate For Life?

Black Guillemots typically reach sexual maturity at around the age of 4. Once they pair up with a mate, they tend to remain in a monogamous relationship for life.

In spring, they return to their breeding grounds and will typically nest close to the site of their previous year’s nesting site.

The Size & Weight Of Black Guillemots

Black Guillemots are relatively small seabirds, smaller than a Guillemot and slightly larger than a Puffin. Both male and female Black Guillemots are similar in size and shape.

How Much Does A Black Guillemot Weigh?

An adult Black Guillemot can weigh anywhere between 300 to 460 grams (10.5 to 16 ounces). Males and females tend to be around a similar weight with juveniles being slightly smaller and lighter.

How Big Is A Black Guillemot?

The average length of an adult Black Guillemot is around 30 to 32 cm (12 to 12.5 inches) with a wingspan of around 52 to 58 cm (20.5 to 23 inches).

Are Black Guillemots Under Threat?

Black Guillemots are currently not considered a species at high risk of extinction and are categorised as a species of Least Concern by the International Union for Conservation of Nature (IUCN). In the UK, they are Amber listed on the UK Birds of Conservation Concern.

Globally the population of Black Guillemots is considered to be stable but they are vulnerable to specific threats that could reduce their numbers over time.

One of the most significant threats to Black Guillemots is climate change which could affect their food sources as well as their breeding sites. Pollution is another issue faced by Black Guillemots and other seabirds. This is a particularly difficult threat as they feed so close to the shoreline.

They also face problems due to human disturbance from coastal development, increased boat traffic and human activity close to nesting sites. Many Black Guillemots also become accidental victims of fishing operations, getting caught up in fishing nets.

What Eats A Black Guillemot?

Black Guillemots face predation from various animals, particularly during the breeding season these include; large gull species like the Great Black-Backed Gull which preys on eggs and chicks as do Crows and Ravens.

On land they face predation from foxes, stoats, weasels and rats that raid nests particularly those nests on low cliffs or at ground level.

Where Can I See Black Guillemots In The UK?

Black Guillemots are seabirds which are mainly found along the rocky coastlines of the UK. Some of the most reported sightings are at the following places;

Scotland

The Isle of Mull & Iona
The Shetland Islands
The Orkney Islands
The Cairngorms National Park (coastal areas)

England

The Isle of Man
Cornwall (particularly the Lizard Peninsula)

Wales

Anglesey
The Pembrokeshire Coast

Northern Ireland

The Causeway Coast
The Mourne Mountains

The best time to spot Black Guillemots in one of the above locations is during the breeding season (late spring to early summer). Although they are still visible during the winter months, they are less active and more dispersed making it more difficult to spot them.

They are more active during the early morning and late afternoon periods and will be easier to spot using a decent pair of binoculars or a spotting scope.

Frequently Asked Questions

Where are Black Guillemots most commonly found in the UK?

Black Guillemots are most commonly found along the rocky coastlines of Scotland, including the Shetland and Orkney Islands, the Isle of Mull, and coastal regions of Northern Ireland, such as the Causeway Coast.

What do Black Guillemots eat?

Black Guillemots primarily feed on small fish and marine invertebrates. Their diet includes species like sculpins, cod, blennies, and crustaceans such as shrimps and crabs.

What are the main predators of Black Guillemots?

The main predators of Black Guillemots include large gulls like the Great Black-Backed Gull as well as Crows and Ravens and mammals such as foxes, weasels, stoats and rats.