Black-Throated Diver Diet and Size: Feeding Habits, Predators, and Measurements

The Black-Throated Diver (Gavia Arctica) nests in the far north of Scotland but can be seen all around the UK coastline during the non-breeding season. Also known as the Black-Throated Loon and the Arctic Loon, the Black-Throated Diver is a skilled diving bird and can catch fish at more than 6 metres under water.

They prefer to nest in small pools and lochs but are sometimes spotted on large lakes and inland reservoirs. In this article we’ll take a close look at the dietary habits, the breeding habits and the conservation status of these interesting diving birds. Keep reading to find out more.

The Dietary Habits Of The Black-Throated Diver

Black-Throated Divers mainly eat fish, but they will also eat a variety of other aquatic organisms if fish are in short supply.

What Does A Black-Throated Diver Eat?

The main prey of the Black-Throated Diver includes small to medium-sized fish like perch, trout, minnows, and sticklebacks. They consume aquatic insects, crustaceans (like crayfish), molluscs, and sometimes amphibians. 

During colder winter months when fish are less plentiful, Black-Throated Divers also eat small amounts of aquatic vegetation.

They hunt by diving underwater, using their sharp eyesight to locate and catch prey. Their bodies are well-adapted to diving, and they can stay submerged for over a minute while chasing prey.

What To Feed A Baby Black-Throated Diver? 

Black-throated Divers feed their chicks a diet that gradually progresses as the chicks grow. During the first few days after hatching, the chicks are fed small aquatic invertebrates and tiny fish that are easy to swallow.

As the chicks grow and develop, larger fish are introduced into their diet. The parents catch the fish and deliver them directly to the chicks, either on the water or at the nest site.

Breeding Habits Of Black-Throated Divers

The breeding habits of the Black-throated Diver are fascinating, involving elaborate courtship rituals like parallel swimming where the pair swim side by side often diving and surfacing together. Another common courtship display involves both birds dipping their heads towards the water or stretching their necks.

During the breeding season, Black-throated Divers become highly territorial. They often return to the same lakes or ponds each year to breed, defending these areas from other loons or birds. 

Both males and females engage in territorial defence, often through vocalisations and posturing. Aggression is mainly displayed toward intruding Loons or other birds rather than direct physical confrontations.

Do Black-Throated Divers Mate For Life?

Black-throated Divers form long-term monogamous pairs, often returning to the same nesting sites year after year. However, they may swap partners if they fail to raise a successful brood or one partner dies.

The Size & Weight Of Black-Throated Divers

Black-Throated Divers are large water birds, bigger than the Great-Crested Grebe but smaller than a Cormorant.

How Much Does A Black-Throated Diver Weigh?

There are differences in the weight of male and female Black-Throated Divers. Males are the larger of the two typically weighing around 3.4 kg whereas females typically weigh around 2.3 kg.

The weight of these birds can alter due to seasonal variations including females might become heavier when carrying their eggs and both birds typically gain extra weight before migrating to warmer areas for winter.

How Big Is A Black-Throated Diver?

The average length of a Black-Throated Diver is around 58 to 73 cm with a wingspan of around 110 to 130 cm. Again it’s the males of the species that are longer and have a wider wingspan.

Are Black-Throated Divers Under Threat?

The Black-throated Diver faces a variety of threats, both natural and human-induced. While they are not currently considered globally endangered, their populations are vulnerable in certain areas due to habitat loss and environmental pressures.

They are currently listed as Least Concern by the International Union for Conservation of Nature (IUCN), indicating that the species is not immediately threatened with extinction. However, their populations are under pressure, particularly in parts of Europe and Asia.

Some local populations, particularly in the UK and parts of Europe, are considered vulnerable due to human activities like pollution, habitat degradation, and disturbance during breeding seasons. The destruction and alteration of their habitat due to agriculture, urbanisation and forestry can have a significant impact on their nesting abilities.

Other human activities like watersports including boating, fishing and tourism can disturb nesting sites causing the birds to abandon their nests and chicks.

Black-Throated Divers rely on clean water for foraging, which means any pollution from oil spills or chemical runoff can significantly affect their food supply. These birds also get accidentally caught up in fishing nets whilst foraging under water which leads to them being drowned.

What Eats A Black-Throated Diver?

Black-Throated Divers also face the threat of predation this is especially true during the nesting and chick rearing stages. Herring Gulls and Great Black-Backed Gulls prey on eggs and young chicks and foxes, minks and otters will raid nests taking eggs and chicks as well.

Due to their size and aquatic lifestyle, adult Black-Throated Divers have  few natural predators. However, large raptors like White-Tailed Eagles or Golden Eagles occasionally prey on them.

Where Can I See Black-Throated Divers In The UK?

Black-throated Divers breed on freshwater lochs in the Scottish Highlands and islands during the summer and migrate to coastal waters around the UK, particularly in western and southern areas, during the winter months.

The best places to spot Black-Throated Divers depends on the season. Below is a list of the places where most reported sightings are made;

During The Breeding Season

• Loch Maree (Wester Ross)
• Loch Ness
• Loch Rannoch (Perthshire)
• Loch Laggan (Highlands)
• The Outer Hebrides

During The non-Breeding Season

England

• Cornwall (Coastal areas like Mount’s Bay, Falmouth, and the Lizard Peninsula)
• Devon (Around Torbay and other coastal sites)
• Morecambe Bay
• Solway Firth
• Poole Harbour
• Portland Bill
• Langstone Harbour
• Chichester Harbour

Wales

• St. Bride’s Bay
• Strumble Head

Northern Ireland

• Strangford Lough
• Lough Foyle

You will have a better chance of spotting Black-Throated Divers during winter when many European birds fly into UK coastal areas as listed above.

SEE ALSO: Swift Diet and Size: Feeding Habits, Predators, and Measurements

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