Loons
| Loons | ||||||||||||
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Common loon ( Gavia always ) |
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| Systematics | ||||||||||||
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| Scientific name of the order | ||||||||||||
| Gaviiformes | ||||||||||||
| Wetmore & Miller , 1926 | ||||||||||||
| Scientific name of the family | ||||||||||||
| Gaviidae | ||||||||||||
| JA Allen , 1897 | ||||||||||||
| Scientific name of the genus | ||||||||||||
| Gavia | ||||||||||||
| Forster , 1788 |
The loons (Gaviiformes, Gaviidae, Gavia ) are an order , family and genus of birds . They are diurnal and nocturnal birds that are tied to bodies of water and inhabit the taiga and tundra of the Holarctic in five species . The temperate zones are usually only reached by train and in winter quarters.
External features
Loons are large swimming and diving birds with a body length of 53 to 91 centimeters and a wingspan between 106 and 152 centimeters. Their weight is between 1 and 6.4 kilograms; the large species are therefore considerably heavier than geese . Of the grebes they differ mainly by full webbed which the three forward-facing toes of anisodactylen connect the foot, and by an externally clearly visible, even if only short tail.
Loons have a streamlined body that is perfectly adapted to aquatic life. The legs start far behind the body and carry strong feet, which perfects the drive in and under water.
In the breeding plumage of most species, their plumage is colored checkerboard-like black and white on the upper side, only in the red-throated diver it is monochrome gray-brown. On the underside it is almost white in all species. It is very dense and insulates well against the cold of the arctic and subarctic waters. The head and neck of all species are very colorful. In winter, the eye-catching splendid dress is replaced by a simpler, calm dress . Males are slightly larger and heavier than females; otherwise there is no visible gender dimorphism . Young loons resemble adult birds in their resting plumage all year round; only when they are around three years old do they show the typical splendor of adult birds.
voice
The characteristic “song” of the loons is an extremely loud and melodic howl that carries you far and is one of the loudest calls that can be heard in the arctic latitudes. This song is only uttered during the breeding season and serves to delimit the territory. In the red diver, both partners call, in the other species only the males call.
Another call is a warning call that is emitted when there is danger. With red-throated, black-throated and Pacific divers this is a raven-like croak, with common loons and yellow-billed ice divers a "screeching laugh".
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distribution and habitat
Loons mainly inhabit the north of the Holarctic , i.e. the tundra and taiga in Canada , Alaska , Greenland , Scandinavia and Russia . With the red-throated diver and the black-throated diver, two of the five species also breed in Northern Europe; the southern limit of the occurrence of both species lies in Europe in the north of Ireland, in the north of Scotland and in the south of Norway and Sweden. The common loon breeds mainly in North America, also in Greenland and Iceland; the yellow-billed diver inhabits northeast Siberia and the far north of America.
Loons spend their entire lives on or in the immediate vicinity of water. The breeding sites of the large species are found in deep lakes in the tundras and boreal zones , with red-throated divers also on small lakes and ponds. If possible, small islands within the lakes are preferred as nesting sites. Red-throated divers and yellow-billed divers breed in rare cases in sheltered sea bays or in river deltas.
The winter quarters are depending on the species on the coasts of Europe, Asia and North America; in Europe they include the North and Baltic Seas and the northern Mediterranean ; in North America they extend south to Baja California and Florida , in Asia they extend down the Chinese coast to Hainan .
The Greenlandic and Icelandic populations of the ice diver can be observed on European coasts in winter and only in exceptional cases on large inland lakes. Red-throated and black-throated divers are more common, and they come to Central European coasts in large numbers in winter. Especially on the autumn migration, both species rest individually or in small groups deep in the central European inland, mostly on large lakes. The northern Siberian black-throated diver populations in particular show particularly interesting migratory behavior. In autumn they migrate to the Black Sea, in spring their migration route first leads them to the Baltic Sea and from there to the White Sea . Such migratory behavior, in which birds return to the breeding area in a different way than in autumn, is known as a loop movement and has so far only been documented for a few bird species.
The yellow-billed diver is an irregular visitor in Central Europe , the Pacific diver has not yet been identified.
Way of life
Locomotion
Loons are excellent divers who dive up to 75 meters deep and can stay underwater for up to eight minutes. Usually the depth is only two to ten meters, and a dive duration of one minute is rarely exceeded. Loons begin a dive by diving straight down without making a forward leap like some other waterfowl (e.g. grebes). Underwater they use their feet as a drive; the wings are rarely used as an aid.
On the other hand, loons move around very awkwardly on land. You cannot stand up straight for a long time, but have to support yourself with your chest. The legs do not allow waddling movement; instead they make short, frog-like jumps that are exhausting and only allow short distances to be covered.
Despite the relatively short wings, loons are good fliers and can cover great distances. Their flight pattern is characterized by a stretched neck, with the head held a little lower than the body; the feet protrude behind the tail. Loons almost always take off from the water surface and land on it. They need a long run-up to get started. Only the relatively small red-throated diver is able to fly up from solid land.
nutrition
Most of the time, loons eat small or medium-sized fish , which they catch on dives and mostly swallow while underwater. Usually other foods are only rarely complementary foods; these can be frogs , crustaceans , mollusks , worms or aquatic insects. However, there are cases in which loons breed in fish-free lakes and then temporarily switch their diet entirely to molluscs or insects.
Loons have a very stretchy esophagus that allows them to swallow relatively large prey. Common loons can swallow trout or even flounder up to 45 centimeters in size and one kilogram in weight . Swallowing large prey may fail in very rare cases; so one has already found loons who choked on (too) large fish.
Reproduction
Loons live in monogamy . Every year during the breeding season, the pairs visit the previous year's territories and stay together during the migration and in the winter quarters. Loons do not breed every year; about every fourth year the pairs set out with the brood. There is no complex courtship ritual for loons. Couples who are new to each other experience a series of synchronous movements on the water; older couples even these few ritualized behaviors are even more restricted.
The mating takes place on the bank. Mating often begins as soon as they arrive in the breeding grounds, and this continues over the next few days. If it happens again and again in the same place, this can create a hollow in the ground, which is often later used as a nest. The nest is made of water plants and mosses. It is always in the immediate vicinity of the shore, almost never further than a meter from the water.
The red-throated diver differs from the larger species in its territory behavior. The latter are territorial and defend the area aggressively against all intruders. On the other hand, the nests of the red-throated divers are often close together, and only the immediate vicinity of the nest is defended. Most of the time threatening gestures are enough to drive away an intruder. There is seldom a fight, which is then fiercely fought and can end with the death of an opponent by drowning or beaking.
One to three, in most cases two, eggs are laid. Both parents brood. After hatching, the young remain in the nest for about three days before going into the water. At this young age you are already able to swim and dive; often they also rest on their parents' backs. The young are fed by the adult birds until they are seven weeks old and sometimes beyond. One of the young birds usually proves to be the stronger early and gets most of the food for itself. If there is not enough food available, this often results in the death of the weaker boy.
The knowledge of the life expectancy of the individual species has so far been unsatisfactory. Red-throated and black-throated divers live more than ten and sometimes even older than twenty years. One black diver was found to be 28 years old. On the other hand, no specimen has been known of the common loon that has reached an age of more than eight years. But this is certainly not the actual maximum age.
Predators
Adult loons have few predators; only large birds of prey such as sea eagles can occasionally prey on a loon. Young birds sometimes fall prey to ravens and crows , seagulls , skuas , otters or large fish . However, the reverse is also documented: a loon stabs a sea eagle.
People and loons
The peoples of northern countries in particular have long had a relationship with these birds. The Eskimos hunt loons and process hides and feathers into clothing. This moderate hunt has never endangered the population. In Scotland it was considered a bad omen to hear a loon calling for territory.
While there is no traditional name for this family of birds in the German language, they are known as loons in English . This term is mainly used in North America; in Scotland it is applied to the common loon. The family is known simply as diverse in the UK . The name loon probably comes from the Old Norse lomr, which is related to the German word "lahm" and could have referred to the awkward movement on land.
No species of loons is threatened. Nevertheless, populations of all species have decreased due to human influences in the Arctic ecosystem. The destruction of banks, the pollution of bodies of water and the laying of drift nets and gillnets in which the animals get caught and drown are responsible for this. In North America, entire populations of ice divers have been found to be contaminated to toxic levels with mercury that they ingested through fish.
Fossil history
The loons are a very old group of birds. While the oldest sure this taxon attributable fossils from the Miocene originate, there are far older finds, whose actual membership of the loons, however, is controversial. Of these, the oldest neo-geornis are wetzeli, of which only fragments of a metatarsal bone ( tarsometatarsus ) have survived, and Polarornis sp., Known for skull fragments and perhaps synonymous with neo-geornis; both fossils are from the Upper Cretaceous . Due to strong similarities with the bone structure of modern loons, they were often assigned to them; other scientists consider this relationship to be very unlikely and see in Neogeornis a Mesozoic water bird, which has developed similar characteristics to the loons in convergent evolution .
The genera Gaviella and Colymboides from Europe and North America, which could represent very early representatives of the Gaviiformes, have been handed down from the Eocene and Oligocene . Colymboides , however, is probably a paraphyletic reservoir of forms, which is defined by the absence of characteristics typical of the recent genus Gavia .
The genus Gavia has been known since the early Miocene . In addition to the five recent species, ten fossil species have been described. Petralca also comes from the lower Miocene , the only known fossil of which was interpreted as a representative of the alkenvirds (Alcidae) until 2017 .
Systematics
External system
Loons are not closely related to any other bird family. That is why they are listed as the only family in the Gaviiformes order.
Traditionally, the loons were placed near the grebes (Podicipedidae), with whom they have some things in common in their outward appearance and way of life. As early as 1758, Carl von Linné assigned both groups to a genus Colymbus in the Systema Naturae , which he classified under the Anseres, an order that included almost all waterfowl in his system. This was done by other zoologists, for example Johann Karl Wilhelm Illiger , who placed Colymbus in the Pygopodidae family together with the alken birds and penguins in 1811. At the end of the 19th century, rag and loons were first divided into two families, but were still considered related. Leon Gardner was the first zoologist in 1925 to question the relationship between sea and ragged divers.
According to later analysis, all similarities between sea and rag divers are due to convergent evolution; a closer relationship between the two diving families is no longer assumed.
More recent DNA analyzes have placed loons in a distant relationship with tube noses , penguins or frigate birds . None of these hypotheses are confirmed and the sister group of loons remains unknown.
Internal system
All loons living today are assigned to a single genus Gavia , which is the only genus of the family Gaviidae and the order Gaviiformes. According to the traditional view, four types belong here, and according to new findings five types:
- Common loon , G. always
- Yellow-billed loons , G. adamsii
- Black-throated diver , G. arctica
- Red-throated diver , G. stellata
- Pacific diver , G. pacifica
The Pacific diver was originally described as a subspecies of the black-throated diver, but is now mostly listed as a separate species.
A possible cladogram of the loons looks like this:
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literature
- Josep del Hoyo et al: Handbook of the Birds of the World. Volume 1: Ostrich to Ducks. Lynx Edicions, Barcelona 1992, ISBN 84-87334-10-5 .
Individual evidence
- ↑ With the beak into the heart: Loons stabs the sea eagle , SPIEGEL online 23 May 2020.
- ^ Anton M. Scheuhammer, Carolyn Atchison, Allan Wong, David Evers: Mercury exposure in breeding Common Loons (Gavia immer) in Central Ontario, Canada. In: Environmental Toxicology and Chemistry . SETAC Press, Pensacola Fla 17.1998,2, 191-196. ISSN 0730-7268
- ↑ Anton M. Scheuhammer, PJ Blancher: Potential risk to common loons (Gavia immer) from methylmercury exposure in acidified lakes. In: Hydrobiologia. Springer, Dordrecht 279 / 280.1994,1, 445–455. ISSN 0018-8158
- ↑ Marcel van Tuinen, S. Blair Hedges: The effect of external and internal fossil calibrations on the avian evolutionary timescale. In: Journal of Paleontology. Ithaca NY 48.2004.1, 45-50. ISSN 0022-3360
- ↑ Gerald Mayr: A partial skeleton of a new fossil loon (Aves, Gaviiformes) from the early Oligocene of Germany with preserved stomach content. In: Journal of Ornithology. Springer, Heidelberg 2004, 145, 281-286. ISSN 0021-8375
- ↑ Avibase , April 26, 2006
- ^ Jon Fjeldså: The Grebes. Oxford University Press, Oxford 2004, ISBN 0-19-850064-5
