The Common Murre is 38-46 cm (15-18 in) in length with a 61-73 cm (24-29 in) wingspan. Male and female are indistinguishable in the field and weight ranges between 945 g (2.083 lb) in the south of their range to 1,044 g (2.302 lb) in the north. A weight range of 775-1,250 g (1.709-2.756 lb) has been reported. In breeding plumage, the nominate subspecies (U. a. aalge) is black on the head, back and wings, and has white underparts. It has thin dark pointed bill and a small rounded dark tail. After the pre-basic moult, the face is white with a dark spur behind the eye. Birds of the subspecies U. a. albionis are dark brown rather than black, most obviously so in colonies in southern Britain. Legs are grey and the bill is dark grey. Occasionally, adults are seen with yellow/grey legs. In May 2008, an aberrant adult was photographed with a bright yellow bill. The plumage of first winter birds is the same as the adult basic plumage. However, the first pre-alternate moult occurs later in the year. The adult pre-alternate moult is December-February, (even starting as early as November in U. a. albionis). First year birds can be in basic plumage as late as May, and their alternate plumage can retain some white feathers around the throat. Some individuals in the North Atlantic, known as `bridled guillemots`, have a white ring around the eye extending back as a white line. The chicks are downy with blackish feathers on top and white below. By 12 days old, contour feathers are well developed in areas except for the head. At 15 days, facial feathers show the dark eyestripe against the white throat and cheek.
Habitat and Distribution
The breeding habitat is islands, rocky shores, cliffs and sea stacks. The range covers eastern Canada and west coast of North America, north and western Europe, Japan, eastern Russia.
The Common Murre can venture far from its breeding grounds to forage; distances of 100 km (62 mi) and more are often observed though if sufficient food is available closer by, birds only travel much shorter distances. The Common Murre mainly eats small schooling forage fish 200 mm (7.9 in) long or less, such as polar cod, capelin, sand lances, sprats, sandeels, Atlantic cod and Atlantic herring. Capelin and sand lances are favourite food, but what the main prey is at any one time depends much on what is available in quantity. It also eats some molluscs, marine worms, squid, and crustaceans such as amphipods. It consumes 20-32 g (0.71-1.13 oz) of food in a day on average. It is often seen carrying fish in its bill with the tail hanging out. The Snake Pipefish is occasionally eaten, but it has poor nutritional value. The amount of these fish is increasing in the Common Murre's diet. Since 2003, the Snake Pipefish has increased in numbers in the North-east Atlantic and North Sea and sandeel numbers have declined.
Courtship displays including bowing, billing and mutual preening. The male points its head vertically and makes croaking and growling noises to attract the females. The species is monogamous, but pairs may split if breeding is unsuccessful. Common Murre eggs are large (around 11% of female weight), and are pointed at one end. Eggs are laid between May and July for the Atlantic populations and March to July for those in the Pacific. The eggs vary in colour and pattern to help the parents recognize them, each egg's pattern being unique. Colours include white, green, blue or brown with spots or speckles in black or lilac. After laying, the female will look at the egg before starting the first incubation shift. Both parents incubate the egg for the 28 to 34 days to hatching in shifts of 1-38 hours.
Calls and Songs
The Common Murre has a variety of calls, including a soft purring noise.