Pigeon ice
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Pigeon Duck ( Cepphus columba ) |
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| Cepphus columba | ||||||||||
| Pallas , 1811 |
The pigeon duck ( Cepphus columba ) is a medium-sized species from the family of alken birds , whose distribution area is the north of the Pacific. It is very similar to the other species of the genus Cepphus , especially the Atlantic black guillemot , which is, however, slightly larger. In its area of distribution, the pigeon duck is one of the easiest seabirds to identify due to the white patches on its wings and bright red feet.
A total of five subspecies are described for this species, some of which differ considerably in body size and weight.
Appearance
Depending on their geographical distribution, pigeon ducks show considerable differences in body size and weight. The average weight varies between 417 and 524 grams, with the subspecies C. c. snowi the lightest and C. c. kaiurka is the heaviest subspecies. The wing length varies between 17.9 and 19.7 centimeters.
Adult birds have blackish brown plumage with a conspicuous white spot on the wings. The dark beak is thin and the legs and feet are red. In winter the upper side is colored gray-black and the underside is white. Pigeon ducks can walk well and have an upright position on land. The beak is long and slender, the upper and lower beak are almost symmetrical and shaped like a dagger. The iris hardly contrasts with the dark plumage, but in some individuals a light eye ring can be seen.
Distribution area
The pigeon duck breeds in smaller colonies on rocky islands and cliffs of the northern Pacific. The occurrences extend from Kamchatka to North America and there along the coast from Alaska to California . In winter, Alaska's pigeon ducks migrate to ice-free sea zones in the south. Californian birds, on the other hand, migrate north to the British Columbia area .
food
Pigeon ducks search for their food near the coast in shallow water zones with underwater vegetation. When looking for food, they stay within a radius of about ten kilometers from their breeding colony.
When looking for food, pigeon ducks start their dives from the surface of the water. They stay in the upper water layers and catch fish, crustaceans and other marine animals. The maximum diving depth determined so far is 30 meters, but they prefer waters with a depth of 10 to 20 meters.
Reproduction
Like the other species of the genus and in contrast to most other alken birds, the pigeon duck lays two eggs. This is probably related to the fact that foraging takes place in the vicinity of the breeding colony, which allows them to get enough food for two nestlings due to the short distances. The breeding colonies are found on islands and headlands with a sufficient supply of rock niches and rocky beaches as well as nearby shallow water zones with a rocky bottom. Wherever predatory mammals such as rats, foxes, minks or raccoons occur, the breeding colonies are only found on inaccessible cliffs. The pigeon duck is a colony breeder, but the colonies are generally very small and usually contain a dozen to a hundred breeding pairs. Larger colonies are rare. The species is very faithful to its breeding site and uses its breeding cave several times. Associated with this is a high level of partner loyalty.
Rock niches are used as nesting sites, but these are usually so deep that the breeding bird is no longer visible from the outside. The eggs are placed in a shallow hollow on the floor lined with small pebbles. But pigeon ducks also dig nesting holes or use caves under tree roots or the abandoned burrows of other sea birds or rabbits. The more unusual nest locations of the pigeon duck include small caves under ship docks, bridges and shipwrecks. Nests have also been found in buildings that are no longer in use. The nesting site is usually no more than 30 meters from the waterline.
The start of the breeding season varies by up to a month, depending on the respective environmental conditions. Typically, breeding birds in California, Oregon, and Washington begin their breeding business in the first half of May. In British Columbia, on the other hand, laying begins in the second half of May to the beginning of July. Pigeon ducks are already in the colony 40 days before the start of laying. Both parent birds breed and have a brood spot large enough to cover both eggs. The two nestlings usually hatch at a distance of one to two days, their hatching weight averages 43.7 grams. They are at least until her third, but each one parent bird continuously usually until their seventh day of life brooded . The nestling food is fish from the start, which is eaten whole by the nestlings. The adult birds each bring a single fish to the nest, which they usually carry across their beak. The parent birds statistically bring between 0.7 and 1.9 fish per hour and nest during the day.
The nestling period averages 38 days and varies between 30 and 53 days. The young birds weigh between 300 and 400 grams when they leave their nest. They reach the water either running or fluttering. So far there is no evidence that the parent birds continue to look after their offspring after they have left the nest. On average, one young bird per breeding pair and year fledged.
Predators and age
The main predators are rats, which eat eggs and nestlings. The North American otter ( Lutra canadensis ) regularly visits individual breeding colonies. The predators also include raccoons and the killer whale . Western gulls , bering gulls , great horned owls , bald eagles , peregrine falcons and sound crows are other predators.
Out of 100 adult pigeon ducks, 20 die each year. The median expected life span is six years. The oldest ringbird found so far was 14 years old.
Duration
The population of pigeon deer is considered stable, but there is only little data on the development of this species. The total population breeds in hundreds of small colonies in a very large area, so that inventories are difficult and completely lacking for some areas. Tens of thousands of pigeon ducks are believed to breed on the Russian coast. The population of pigeon ducks breeding in Alaska was estimated by the United States Fish and Wildlife Service in 1993 at 200,000. British Columbia has 10,200, Washington 6,000, Oregon 3,500 and California 15,470 pigeon ducks. The largest breeding colony is on one of California's Farallon Islands . One of the causes of danger is oil pollution in the sea, for example the pigeon ducks were affected by the accident of the super tanker “ Exxon Valdez ” in 1989. However, since pigeon ducks are spread over numerous small colonies, the impact of such disasters on the total population is not very high. The introduction of predatory mammals has negative effects. In the Aleutian Islands, for example, the arctic fox was released for fur breeding purposes, which endangers the ground-breeding pigeon ducks. In British Columbia, raccoon expansion poses a threat to this species.
Subspecies
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The following subspecies of the pigeon duck are distinguished:
- Cepphus columba eureka Storer , 1950 - North American west coast from Oregon to California
- C. c. adianta Storer , 1950 - North American West Coast from Washington to Alaska and the Aleutian Islands
- C. c. kaiurka Portenko , 1937 - Aleutians via the Andreanof Islands , Delarof Islands , Rat Island and Near Islands to the Commander Islands
- C. c. columba Pallas , 1811 - Siberian coast of the Bering Strait to the southern tip of the Kamchatka Peninsula and the coastal area of Alaska
- C. c. snowi Stejneger , 1897 - comes on the Kuril ago
The body size of the subspecies decreases continuously from California to the Aleutian Islands.
supporting documents
literature
- Anthony J. Gaston, Ian L. Jones: The Auks (= Bird Families of the World. Vol. 4 (recte 5)). Oxford University Press, Oxford et al. 1998, ISBN 0-19-854032-9 .
Single receipts
- ↑ Gaston et al., P. 180
- ↑ Gaston et al., P. 178
- ↑ Gaston et al., P. 182
- ↑ a b Gaston et al., P. 184
- ↑ a b Gaston et al., P. 186
- ↑ a b c Gaston et al., P. 185
- ↑ a b Gaston et al., P. 179
- ↑ Gaston et al., P. 179 and p. 180
- ↑ Gaston et al., P. 180
Web links
- Cepphus columba in the endangered Red List species the IUCN 2008. Posted by: BirdLife International, 2008. Accessed January 31 of 2009.
- Videos, photos and sound recordings of Cepphus columba in the Internet Bird Collection