Gray-water dipper
| Gray-water dipper | ||||||||||||
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Gray-water blackbird ( Cinclus mexicanus ) |
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| Cinclus mexicanus | ||||||||||||
| Swainson , 1827 |
The gray water dipper ( Cinclus mexicanus ) is the only representative of the dipper (Cinclidae) native to North America . Like all other species in this family, the up to 20 centimeters tall, uniformly dark slate-gray bird is closely tied to life along smaller flowing waters that are rich in currents and oxygen. Five subspecies are currently recognized.
Appearance
The gray-water dipper is a uniformly dark gray colored, rounded, large-headed and long-legged songbird. It is unmistakable in its area of distribution.
The entire plumage appears dark gray, sometimes almost black. Up close, the slightly lighter areas on the throat and chest as well as the even darker ones on the crown can be seen. Some individuals have slightly brownish tint on the wings. Sometimes the entire head, neck and neck plumage is dark brown. Some ends of the wings of the hand have a light border, but this coloring feature can only be seen from close proximity. The underside is flaked on a slate-gray background, differently distinctly light gray. As with all dippers, the sexes are the same color, but the females are slightly smaller and lighter on average over the year. However, these differences cannot be identified by field ornithology. The iris is dark brown, the beak gray-brown; Legs and toes are slightly pink to flesh-colored.
The fledglings are very similar on top to the adults; the underside, however, is clearly speckled gray and white; the throat area, and in some individuals also the cheeks, is light gray-white.
voice
The main call is a very loud jit or jik that can be heard in a quiet environment up to 1.5 kilometers away . The singing performed by both sexes is a mixture of melodious chatter, individual whistles and rough, pressed tones.
distribution and habitat
The gray-water blackbird is common in western North and Central America. The species does not occur east of the Rocky Mountains .
The gray-water blackbird colonizes North America from the Aleutian Islands southwards across the southwestern part of Alaska , western Canada, including the offshore islands and the northwestern USA, where the closed range changes into many partially isolated areas. The easternmost occurrences are in the eastern foothills of the Rocky Mountains from Alberta to New Mexico . In the Great Basin and the southwestern United States, it is not common except for small isolated populations. In Mexico it occurs in an elongated belt from Chihuahua in the north to Puebla ; in Central America it is represented in highly fragmented occurrences in the low and high mountain ranges up to Panama . Outside the breeding season, it can also be found in larger rivers, lakes and beaver ponds, and occasionally on the seashore.
As early as 1965, dippers were reported from the Venezuelan state of Carabobo ; In 1995 ornithologists from the Czech Republic also saw dipper there, which resembled the gray-water dipper in appearance and behavior. The observation site is about 1,600 kilometers from the nearest known breeding site in Panama. It has not yet been clarified whether these reports are a subspecies of the gray-water dipper, a new species of dipper or an incorrect observation. The IUCN , however, lists Venezuela as a state in which the gray-water blackbird occurs.
The habitats of the gray-water blackbird correspond to those of the other species of Cinclus . During the breeding season, it prefers habitats along fast flowing larger streams and smaller rivers. Unobstructed, bushy or loosely tree-lined, boulder-lined bank sections with niches and ledges offering nesting opportunities are important. Rivers in dense forest sections are less favorable, but are used on a case-by-case basis.
As long as the waters do not freeze over, most of the gray water blackbirds remain in the breeding area and endure extremely low temperatures there. For example, a gray-water dipper north of the Arctic Circle was seen foraging at minus 57 degrees. If the waters freeze over, gray water dippers migrate downstream and to the Pacific coast. The river system is usually not left. The migratory movements are generally small, but can amount to several hundred kilometers, especially in the northern breeding areas.
The gray-water dipper is territorial both during the breeding season and in winter. Often the breeding and winter territories are identical. The size of the breeding territories varies from about 400 meters to several kilometers. The territory generally includes both banks and also includes brooks and beaver ponds. In winter, the density of occurrence of gray-water blackbirds along the remaining ice-free waters is greater, and the claimed and defended territories are correspondingly smaller. Very high distribution densities can be observed, such as 35 gray water blackbirds on the Okanagan River on just one kilometer of the river.
The lack of the gray-water dipper in the entire eastern half of North America remains unexplained, although a myriad of suitable habitats are available in the Atlantic provinces of Canada , New England and the Appalachians , for example . Probably the species only survived during the last ice age in favored areas of western North America and was not able to cross the inhospitable regions of the Prairie Provinces and the Great Plains afterwards .
Food and subsistence
The food of the gray water dipper hardly differs in its composition from that of other diving dipper. It consists largely of the larvae of caddis flies , stone flies and mayflies . In addition, the sex animals of these species are eaten as well as a number of other insects living on the water, such as midges and other two-winged animals . Other invertebrates such as spiders , crabs or worms only play a subordinate role. Likewise quantitatively rather insignificant are small fishes, especially sculpins and trout - and grayling breeding and fish spawning. However, when salmon migrate on a large scale , their spawn can temporarily become an important source of food.
Most of the food animals are caught swimming and diving. Often it also searches the banks for prey or picks insects from the stones in their breeding waters. Hunts for flying insects and high seat hunts with short missed flights are observed less often. Smaller prey animals are swallowed immediately, larger ones brought ashore or onto the ice and prepared there for consumption; occasionally gray water blackbirds also lay several prey on the ice for later consumption.
Breeding biology
Like all dippers, the gray-water dipper also becomes sexually mature at the end of its first year of life. Pair formation begins in late winter; The most important courtship elements are singing together in particularly attractive places in the territory, feeding the female and pursuit flights along the breeding water. Most gray-water blackbirds lead a monogamous seasonal marriage, in which mating of last year's partners is not uncommon. Polygynia was regularly detected at varying rates; their occurrence seems to be highly dependent on the availability of nesting sites. The nest is built from the end of February by the Central American populations, from March by the dippers that breed in North America, mainly by the female. It is a typical round dipper construction with a side entrance. The outer shell is made of moss that is tightly interwoven with grasses, the inner bowl is made up of grasses and leaves and lined with soft materials. The nesting sites are always in the immediate vicinity of the water, preferably in niches and hollows of rocks along the banks, occasionally also on blocks in the middle of the watercourse; Often places are chosen under washed-out roots, ledges behind waterfalls, but also nesting opportunities on human structures such as bridges or sluices. Nests that are built in niches or on covered ledges are occasionally not closed at the top.
The first clutches are found in March in the lower elevations of North America and as early as the end of February in Central America. In North America, a full clutch consists of 3–6, usually 4–5, pure white, longitudinally elliptical eggs with an average size of 25 × 18 millimeters. The clutches of the Central American populations seem to be somewhat smaller. Additional clutches are the rule when the clutch is lost early, second clutches are very common in the more moderate breeding areas. The eggs are only incubated by the female for about 14-17 days. During the nestling period, which lasts 24–26 days, both partners look after the young. After leaving, the young birds are looked after by their parents for up to three weeks; then they leave the area. In their diversionary migrations , they rarely move more than 50 kilometers from the vegetation, but very often change the river system.
Systematics
The gray-water dipper is the only species of dipper found in North and Central America. Five subspecies, some of which are very poorly differentiated, are described:
- Cinclus mexicanus unicolor Bonaparte , 1827: The subspecies described above occurs in the distribution areas of the USA and Canada.
- C. m. mexicanus Swainson , 1827: The nominate form is represented in the mountains of Mexico southwards to Puebla. One message also affects southern Arizona . Her head and neck are dark brown-black; the young birds are clearly speckled rust-red on the underside on a black-brown background.
- C. m. dickermanni A. R. Phillips , 1966: This subspecies breeds in some isolated islands in southern Mexico, especially in the states of Guerrero , Veracruz and southern Oaxaca . It is very similar to the nominate form, but shows a slate-gray color on the cheeks.
- C. m. anthonyi Griscom , 1837: The North Central American breed occurs in isolated regions in Guatemala , Honduras and Nicaragua . The dorsal plumage is lighter and paler in color than in the aforementioned subspecies.
- C. m. ardesiacus Salvin , 1827: The subspecies with the southernmost distribution breeds in Costa Rica and the northwestern part of Panama . It differs greatly from the other subspecies: Overall, it is significantly paler and lighter in color than the ones mentioned, the ventral side is relatively light ash gray. In juveniles, the throat and much of the abdomen are white.
Existence and endangerment
According to the IUCN, the gray water blackbird population is not endangered. The population estimates are in excess of 600,000 individuals. In addition to natural enemies, which include, above all, various birds of prey , martens and occasionally fish, environmental events such as floods during the breeding season and widespread, rapid freezing of food waters also have a population-regulating effect . Regionally, populations can be endangered and made to disappear by flood barriers, dam construction, river straightening and similar interventions in the habitat of the species; The gray-water blackbird is also very sensitive to the introduction of pollutants into its breeding waters.
Individual evidence
- ↑ Brewer (2001) p. 204
- ↑ a b Cinclus mexicanus in the endangered Red List species the IUCN 2011. Posted by: BirdLife International, 2009. Accessed November 13, 2011th
- ↑ Kingery (1996) Winter Range
- ^ Kingery (1996) Territoriality
- ↑ Kingery (1996) Winter Range
- ↑ Brewer (2001) p. 205
- ^ Kingery (1996) Treatment Of Food Items.
- ^ Kingery (1996) Mating System And Sex Ratio.
- ↑ Brewer (2001) p. 205
- ↑ Kingery (1996) Immature Stage
- ↑ Brewer (2001), p. 204.
- ^ Kingery (1996) Predation.
literature
- David Brewer, Barry Kent MacKay: Wrens, Dippers and Thrashers. Yale University Press New Haven CT et al. 2001, ISBN 0-300-09059-5 , pp. 19, 62-63 and 199-202.
- Gerhard Creutz : The dipper. Cinclus cinclus. 2nd, revised edition. A. Ziemsen, Wittenberg 1986, ISBN 3-7403-0008-6 ( Die neue Brehm-Bücherei 364).
- Hugh E. Kingery: American Dipper (Cinclus mexicanus). In: A. Poole (Ed.): The Birds of North America Online. Cornell Lab of Ornithology, Ithaca NY 1996.
- Gary Voelker: Molecular phylogenetics and the historical biogeography of dippers. (Cinclus). In: Ibis. Volume 144, Issue 4, October 2002, pp. 577-584, doi : 10.1046 / j.1474-919X.2002.00084.x .
