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Guillemots

Guillemots - http://www.flickr.com/photos/gordiesbirdies/

The 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 (100–200 ft), and depths of up to 180 m (600 ft) have been recorded.

Common Murres breed in colonies at high densities, nesting pairs may be in bodily contact with their neighbours. They make no nest, their single egg is incubated on bare rock. Eggs hatch after ~30 days incubation. The chick is born downy, and can regulate its body temperature after 10 days. They leave the nest site in around 20 days accompanied by the male parent. Chicks cannot fly when they leave the nest but are capable of diving as soon as they hit the water. The female stays at the nest site about 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.

DescriptionEdit

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 lb) in the south of their range to 1044 g (2.3 lb) in the north. 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. This is not a distinct subspecies, but a polymorphism which 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.

FlightEdit

The Common Murre flies with fast wing beats and has a flight speed of 50 mi/hr (80 km/h). Groups of birds are often seen flying together in a line just above the sea surface. However, a high wing loading of 2g/cm² 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.

DivingEdit

This bird 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 50 m (160 ft) on a regular basis. Diving depths up to 180 m (600 ft) have been recorded and birds can remain underwater a couple of minutes.

Ecology and behaviourEdit

FeedingEdit

The Common Gulliemot can venture far from its breeding grounds to forage; distances of 100 km 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 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 grams 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.

CommunicationEdit

The Common Guillemot has a variety of calls, including a soft purring noise.

ReproductionEdit

ColoniesEdit

This species nests in densely-packed colonies (known as "loomeries"), with up to twenty pairs occupying one square metre at peak season. Common Murres do not make nests and lay their eggs on bare rock ledges, under rocks, or the ground. They first breed at four to six years old and average lifespan is about 20 years.

Immature birds return to the natal colony, but from age 5 onwards ~25% of birds leave the colony, perhaps dispersing to other colonies.

High densities mean that birds are close contact with neighbouring breeders. Common Murres perform appeasement displays more often at high densities and more often than Razorbills. Allopreening is common both between mates and between neighbours. Allopreening helps to reduce parasites, and it may also have important social functions. Frequency of allopreening a mate correlates well with long-term breeding success. Frequency of allopreening a neighbour correlates well with current breeding success. Allopreening may function as a stress-reducer; ledges with low levels of allopreening show increased levels of fighting and reduced breeding success.

CourtshipEdit

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.

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