The Common Murre or Common Guillemot (Uria aalge) is a large auk. It is also known as the thin-billed murre in North America. It has a circumpolardistribution, occurring in low-Arctic and boreal waters in the North Atlantic and North Pacific. It spends most of its time at sea, only coming to land to breed on rocky cliff shores or islands.
Common murres have fast direct flight but are not very agile. They are more maneuverable underwater, typically diving to depths of 30–60 m (98–197 ft). Depths of up to 180 m (590 ft) have been recorded.
Common murres breed in colonies at high densities. Nesting pairs may be in bodily contact with their neighbors. They make no nest; their single egg is incubated on a bare rock ledge on a cliff face. Eggs hatch after ~30 days incubation. The chick is born downy and can regulate its body temperature after 10 days. Some 20 days after hatching the chick leaves its nesting ledge and heads for the sea, unable to fly, but gliding for some distance with fluttering wings, accompanied by its male parent. Chicks are capable of diving as soon as they hit the water. The female stays at the nest site for some 14 days after the chick has left.
Both male and female common murres moult after breeding and become flightless for 1–2 months. In southern populations they occasionally return to the nest site throughout the winter. Northern populations spend the winter farther from their colonies. The auks are a family of seabirds related to the gulls and terns which contains several genera. The common murre is placed in the guillemot (murre) genus Uria (Brisson, 1760), which it shares with the thick-billed murre or Brunnich's guillemot, U. lomvia. These species, together with the razorbill, little auk and the extinct great auk make up the tribeAlcini. This arrangement was originally based on analyses of auk morphology and ecology.
The binomial name derives from Greek ouriaa, a waterbird mentioned by Athenaeus, and Danish aalge, "auk" (from Old Norse alka) he English "guillemot" is from French guillemot, probably derived from Guillaume, "William". "Murre" is of uncertain origins, but may imitate the call of the common guillemot.
Some individuals in the North Atlantic, known as "bridled guillemots", have a white ring around the eye extending back as a white line. This is not a distinct subspecies, but a polymorphism that becomes more common the farther north the birds breed—perhaps character displacement with the northerly thick-billed murre, which has a white bill-stripe but no bridled morph. The white is highly contrasting especially in the latter species and would provide an easy means for an individual bird to recognize conspecifics in densely packed breeding colonies.
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.[11]
The common murre flies with fast wing beats and has a flight speed of 80 km/h (50 mph). Groups of birds are often seen flying together in a line just above the sea surface.[6] However, a high wing loading of 2 g/cm2[13] means that this species is not very agile and take-off is difficult. Common murres become flightless for 45–60 days while moulting their primary feathers.[15]
The common murre is a pursuit-diver that forages for food by swimming underwater using its wings for propulsion. Dives usually last less than one minute, but the bird swims underwater for distances of over 30 m (98 ft) on a regular basis. Diving depths up to 180 m (590 ft) have been recorded[16] and birds can remain underwater a couple of minutes.