Thick-billed murre

The thick-billed murre or Brünnich's guillemot (Uria lomvia) is a bird in the auk family (Alcidae). This bird is named after the Danish zoologist Morten Thrane Brünnich. The very deeply black North Pacific subspecies Uria lomvia arra is also called Pallas' murre after its describer.

Taxonomy

The thick-billed murre was formally described in 1758 by the Swedish naturalist Carl Linnaeus in the tenth edition of his Systema Naturae. He placed it with the other auks in the genus Alca and coined the binomial name Alca lomvia. Linnaeus specified the type locality as boreal Europe but this was restricted in 1921 to Greenland by the German ornithologist Ernst Hartert. The thick-billed murre is now placed together with the common murre in the genus Uria that was introduced in 1760 by the French zoologist Mathurin Jacques Brisson. The genus name is from Ancient Greek ouria, a waterbird mentioned by Athenaeus. The specific epithet lomvia is a Swedish word for an auk or diver. The 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.

Four subspecies are recognised: The thick-billed murre and the closely related common guillemot (or common murre, U. aalge) are similarly sized, but the thick-billed still bests the other species in both average and maximum size. The thick-billed murre measures in total length, spans across the wings and weighs . The Pacific race (U. l. arra) is larger than the Atlantic race, especially in bill dimensions.

Adult birds are black on the head, neck, back and wings with white underparts. The bill is long and pointed. They have a small rounded black tail. The lower face becomes white in winter. This species produces a variety of harsh cackling calls at the breeding colonies, but is silent at sea.

They differ from the common murre in their thicker, shorter bill with white gape stripe and their darker head and back; the "bridled" morph is unknown in U. lomvia – a murre has either a white eye-stripe, or a white bill-stripe, or neither, but never both; it may be that this is character displacement, enabling individual birds to recognize conspecifics at a distance in the densely packed breeding colonies as the bridled morph is most common by far in North Atlantic colonies where both species of guillemots breed. In winter, there is less white on the thick-billed murre's face. They look shorter than the common murre in flight. First year birds have smaller bills than adults and the white line on the bill is often obscure, making the bill an unreliable way to identify them at this age. The head pattern is the best way to distinguish first-year birds from common murres.

Distribution and habitat

thumb|Adult and chick, [[Buldir Island, Alaska]]

The thick-billed murre is distributed across the polar and sub-polar regions of the Northern Hemisphere where four subspecies exist; one lives on the Atlantic and Arctic oceans of North America (U. l. lomvia), another on the Pacific coast of North America (U. l. arra), and two others that inhabit the Russian arctic (U. l. eleonorae and U. heckeri).

Thick-billed murres spend all of their lives at sea in waters which remain below 5°C, except during the breeding season where they form dense colonies on cliffs. and has also been recorded in the Netherlands. In the western Atlantic, they may range as far as Florida, and in the Pacific to California.

Behaviour and ecology

Breeding

thumb|left|Breeding colony at [[Stappen, Bear Island. Note bill-stripes visible at a distance.]]

thumb|upright=0.8|Egg, Collection [[Museum Wiesbaden]]

Thick-billed murres form vast breeding colonies, sometimes composed of over a million breeding birds, on narrow ledges and steep cliffs which face the water. Despite this, they are one of the most abundant marine birds in the Northern Hemisphere. Due to the enormous amount of energy needed to take off in flight, adults can only provide one food item at a time to their chick. Older and experienced adults obtain the better nesting sites located in the center of the colony, while the inexperienced individuals are kept on the margins where their young are more likely to be preyed upon.

Food and feeding

thumb|right|Vagrant adult in winter plumage, northern [[South Carolina]]

thumb|right|Thick-billed murres in [[Alaska Maritime National Wildlife Refuge]]

thumb|right|A thick-billed murre (second from right, distinguishable by white marking on bill) with a group of [[common murres in Reykjanes, Iceland]]

The thick-billed murre's flight is strong and direct, and they have fast wing beats due to the short wings. Like the other auks, these birds forage for food by using their wings to 'swim' underwater. They are accomplished divers, reaching depths of up to 150 m and diving for up to four minutes at a time; usually however birds make either shallow short dives or dive down to 21–40 m for longer periods. While hunting, the diving trajectory resembles a flattened 'U'.

The diving depths and durations regularly achieved by these birds indicate that they, and similar auks, have some—as yet unknown—mechanism to avoid diving sickness and lung collapse when surfacing.

Status and conservation

Although declines have been observed in many parts of their range, the thick-billed murre is not a species of concern as the total population is estimated to contain between 15 and 20 million individuals worldwide. In the Barents Sea region, the species has declined locally, due to influences associated with polar stations in Russia. Fisheries may also be a threat, but because thick-billed murres are better able to use alternative food sources the effect of over-fishing is not as severe as on the common murre. Pollution from oil at sea exerts another major threat. Murres are among the seabirds most sensitive to oil contamination. Incidental mortality brought on by entanglement with fishing gear is also an important cause of population decline.

Thick-billed murres are closely associated with sea-ice throughout the year. However the species seems adaptable. Populations at the southern edge of their range switched from feeding on ice-associated Arctic cod to warmer-water capelin as ice break-up became earlier. Dates for egg-laying advanced with the earlier disappearance of ice. The growth of chicks is slower in years when ice break-up is early relative to egg-laying by the murres. In extremely warm years, mosquitoes and heat kill some breeders.

References

Sources

Evans, Peter, G.H & Kampp, K. (1991): Recent changes in Thick-billed Murre populations. In: Gaston, A.J & Elliot, R.D. (eds.): Studies of high-latitude seabirds: 2. Conservation biology of Thick-billed Murres in the Northwestern Atlantic. Canadian Wildlife Service Occasional Paper 69: 7–14.
Gaston, Anthony J.; Nettleship, David N. (1981): The Thick-billed murres of Prince Leopold Island. Canadian Wildlife Service Monograph No. 6, Environment Canada, Ottawa.
Gaston, Anthony J.; Jones, Ian L. (1998): The Auks: Alcidae, Bird Families of the World, Oxford: Oxford University Press.
Lilliendahl, K.; Solmundsson, J.; Gudmundsson, G.A. & Taylor, L. (2003): Can surveillance radar be used to monitor the foraging distribution of colonially breeding alcids? [English with Spanish abstract] Condor 105(1): 145–150. DOI: 10.1650/0010-5422(2003)105[145:CSRBUT]2.0.CO;2 HTML abstract
Nettleship, David N. (1996): 3. Thick-billed Murre. In: del Hoyo, Josep; Elliott, Andrew & Sargatal, Jordi (eds.) (1996), Handbook of Birds of the World (Volume 3: Hoatzin to Auks): 710–711, plate 59. Lynx Edicions, Barcelona.