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 circumpolar distribution, 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 manoeuvrable underwater, typically diving to depths of 30–60 m (98–197 ft). Depths of up to 180 m (590 ft) have been recorded.
At first glance, the common murre appears penguin-like, as the breeding adults are dark brown-black on the head, neck and back with a white underbelly and white tipped secondary feathers. They are about 38-43cm in length and stand upright like a penguin when on land. They have dark, long, and slender bills and dark greyish-black feet and legs. They have a wingspan of 64-71 cm. The adult winter plumage is mostly identical except for white on the cheeks and throat and a dark spur extending back from the eye. An alternate form, or the bridled morph, only occurs in a population in the North Atlantic. It has an eye ring with a line extending toward the back of its head in addition to the regular adult plumage. Chicks are downy when first hatched. They are blackish brown on top and white underneath. When they are first hatched they weigh 55-95 grams. Juveniles are similar to adults except for their smaller size and darker heads.
During breeding, the common murre populations of the Pacific Ocean range from coastal areas of western Alaska to central California. The Atlantic Ocean populations range from Labrador to Nova Scotia. They spend the winters close to the breeding areas but their range extends to southern California in the Pacific populations and to Maine in the Atlantic populations.
The common murre is primarily a pelagic species. It spends the majority of its time at sea except for during breeding season. The breeding season is spent on costal cliffs or offshore islands that are primarily rocky.
The first breeding season takes place at the age of 4-6 years. The common murre does not use nesting material, as the one egg is laid on the bare rock or soil of a steep cliff or ledge facing the sea. The egg is pyriform or pear-shaped which prevents it from rolling off of the ledge. This is because the egg pivots around the pointed tip when it is disturbed. The shape also maximizes the amount of surface area that will be in contact with the parent's brood patch during incubation. Eggs are laid between May and July in populations breeding on the Atlantic coast and between March and July on the Pacific coast. The eggs vary in colour from pure white to shades of green, blue, or brown with spots or speckles of brown, lilac, or black. These various colour forms are important for egg recognition by parents. Both parents participate in the incubation process, which takes between 28 and 34 days and is divided into 12-24 hour shifts. Chicks of the common murre are semiprecocial. Chicks fledge (leave the nest) at 18-25 days and go out to sea with the male of the pair. The chick is able to fly at the age of 39-46 days.
Justification (IUCN Red List)
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be increasing, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.