Thick-billed Murre

The Thick-billed Murre, also known as Brunnich's Guillemot, is a stocky, cold-hardy auk adapted to the high Arctic, breeding farther north than its close relative the Common Murre. Plumage is glossy black to dark brown above and white below, similar in overall pattern to the Common Murre, but the bill is noticeably shorter, deeper, and thicker, with a thin pale line running along the base of the upper mandible (the gape stripe) that is diagnostic at close range.

As one of the most numerous seabirds of the Arctic, Thick-billed Murres form vast breeding colonies on sheer cliff faces, often alongside kittiwakes and other seabirds, and are superbly adapted for deep diving in cold northern waters.

Key field marks

• Short, thick, deep-based black bill
• Pale stripe along the gape (base of the bill)
• Sharper, straighter border between the dark throat/breast and white belly than in Common Murre
• Dark brown-black upperparts, white underparts

Similar species

• Common Murre has a longer, thinner, more pointed bill without a pale gape stripe, and a less sharply defined breast border.
• Razorbill has a deep, laterally flattened bill crossed by a white line, differing from the murre's more slender bill shape.
• In winter plumage, both murre species show white on the face, and bill shape remains the most reliable distinguishing feature.

Thick-billed Murres breed on steep sea cliffs across the high Arctic and subarctic, including Greenland, Arctic Canada, Svalbard, Novaya Zemlya, and the Bering Sea region, generally nesting farther north than Common Murres. Outside the breeding season, birds move south to ice-free waters, often following the edge of pack ice, and can be found well offshore in the North Atlantic and North Pacific during winter.

The species is highly adapted to cold northern seas, foraging in areas where sea ice and productive upwellings concentrate prey close to breeding colonies.

Behavior

Excellent divers, Thick-billed Murres can descend to depths of over 100 meters, propelling themselves with their wings to pursue fish and invertebrates in cold Arctic waters.

Voice

Colonies produce a constant low growling and croaking chorus, generally deeper and harsher than the calls of Common Murres.

Feeding

Diet includes small Arctic fish such as polar cod and capelin, along with crustaceans and squid, caught during deep dives.

Nesting and breeding

A single pointed egg is laid on bare cliff ledges without nest material, an adaptation that reduces the risk of the egg rolling off; as in the Common Murre, chicks leap from the cliff to the sea before fledging, accompanied by an adult male, to complete their development on the water.