Aegolius
| Aegolius | ||||||||||
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Little Owl ( Aegolius funereus ) |
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| Systematics | ||||||||||
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| Scientific name | ||||||||||
| Aegolius | ||||||||||
| Kaup , 1829 |
Aegolius is a genus from the family of the real owls (Strigidae). It includes small, as oddities called owls, which are almost exclusively nocturnal and their habitats are located in dense forests or other woodlands. Currently, four species are distinguished, which are distributed in the Holarctic as well as in North-Central and South America. In Central Europe the rough owl ( Aegolius funereus ) occurs, after which the genus is sometimes referred to with the German name Raufußkäuze.
Owls feed on small mammals and birds, and the South American species also feed on insects. They breed in natural tree hollows or in old woodpecker holes. All species are largely resident birds .
No species currently appears in any of the IUCN endangerment levels. The generic name comes from the Greek. It was one of the many names for owl in ancient Greece.
features
Owls of the genus Aegolius are small birds with a very large head. No species has feather ears. The upper side plumage of all four species is gray-brown to deep brown. With the exception of the ridgway owl ( Aegolius ridgway ), it is speckled with whitish in different intensities in all species. The large head of the barnacle owl is usually gray and speckled clearly white, in the other species it corresponds in color to the upper side plumage. A large, clear face veil is formed in all species. In the rough owl and the great owl ( Aegolius acadicus ) this is light, sometimes almost white and, especially in the saw owl, it is conspicuously reddish-brown with radial dotted lines, in the yellow-headed owl ( Aegolius harrisii ) it is yellow and in the ridgway owl rust-red. It is bordered by a mostly dark feather border, only in the Ridgway owl it is white. The underside plumage of the rough-owl is drawn lengthways on a light background like a spear-tip, brown-gray in the saw owl rather reddish-brown longitudinally. The two Neotropical species are more colorful: The underside of the yellow-faced owl is light yellow, the throat and chest of the ridgway owl are rust-brown, while the belly and rump are yellow. The yellow-fronted owl also wears a striking yellow neck band. The iris of the eyes is yellow or orange in all species, the downwardly curved hook beak is also yellow or dark horn-colored.
The wings are of medium length, broad and slightly rounded. They show a hint of light banding on the top. The tail is broad, rather short and slightly rounded. The toes of the rough owl and the sawtooth owl are feathered up to the claws, but in the other two species they are bare.
The sexes do not differ in color. However, the females of the rough owl and the great owl appear to be significantly heavier than the males. Whether this weight dimorphism also exists in the other two species is uncertain due to the sparse data situation.
The ears are very high in the head and are arranged asymmetrically. This asymmetry not only includes the external auditory canal, but also the tympanic cavity .
measurements and weight
The smallest representative of this genus is the saw owl. With a weight of around 100 grams, it reaches a total length of around 19 centimeters. With a length of up to 26 centimeters and a weight of up to 194 grams, the Holarctic rough-owl is significantly larger and heavier. In between are the two neotropical representatives of the genus.
Vocalizations
The owls of this genus have a number of vocal expressions. Most impressive is the territory song of the male barnacle owl, which consists of a louder and faster succession of clear hu elements. The tawny owl's territory song consists of soft Tüö elements reminiscent of the sound of falling water droplets , which are performed not very quickly, but persistently. The owl got its peculiar name from its screeching aggression call, which is reminiscent of the sharpening of a saw blade. The Ridgeway owl is very similar to that of the saw owl. The individual elements are, however, a bit lower in pitch and sound a little melancholy. The yellow- fronted owl's territorial song , on the other hand, is a high- pitched , trembling staccato of gürrr elements that are repeated at a very rapid pace. In addition, quite high- pitched u- tones can be heard from this owl . In addition to these main chants, these owls have a number of different, sometimes harsh and screeching calls.
All owls of this genus are acoustically active especially in the period of territorial delimitation and in the early mating season. Once mated, they behave extremely secretly. Even strong predation pressure can lead to a very limited acoustic presence.
distribution and habitat
The most widespread of the four species of the genus is the rough owl, which occurs in the entire boreal zone from Alaska to Kamchatka on the Asian Pacific coast. In addition, there are relic occurrences in America as well as in Europe, which in America are mainly limited to the Rocky Mountains , in Europe to the Central European low mountain ranges , the Pyrenees , the Balkans , the Dinaric Mountains and the Alps . In North America, it shares large parts of its range with the saw owl, which, however, penetrates further south and populates the eastern flank of the Rocky Mountains to a greater extent than the rough-owl. The yellow-faced owl inhabits the eastern slopes of the Andes from Venezuela in the north to northern Argentina. Another large distribution area is in southeastern Brazil, in Uruguay , Paraguay and in the extreme northeast of Argentina. The Ridgway Owl, which occurs in Central America from Mexico to Western Panama, has the smallest distribution area .
The habitats of these owls vary according to their geographical distribution, but they are always forest areas, or at least loosely tree-lined landscape structures. The Holarctic rough-owl lives in particular in the boreal belt of coniferous forests, which mainly consists of different species of spruce and fir , but also occurs in mixed forests with birch , beech and oak . In addition to a sufficient supply of food, the existence of breeding caves and the absence of predators (especially larger owls, especially tawny owls or barred owls and various marten ) are prerequisites for a settlement of this species. In the Palearctic the black woodpecker is the most important supplier of caves, in North America it is the helmeted woodpecker .
The habitat requirements of the owl are similar; however, a certain preference for more humid habitats can be observed in him. In its southern distribution areas it mostly inhabits open woodland with oaks and pines , where it also populates smaller, river-side trees with poplars and alders .
The Ridgway Owl occurs in its Central American breeding areas in particular in montane forests with oak and pine trees, but also populates pastureland if some tall trees are present. Similar habitats form the habitat of the yellow- fronted owl, which visits open walnut stands interspersed with scrub or pasture , alder trees and occasionally also Polylepis stands near or above the tree line.
The rough owl and the sawtooth owl occur in their northern and northeastern distribution areas both in the lowlands and in locations up to 1000 meters or a little above. In the southern regions of their distribution, they are largely tied to montane forests at altitudes of over 1500 meters, where the rough owl occurs as a breeding bird up to close to the tree line around 3000 meters; the highest nesting places of the owl are about 500 meters lower. In Europe, outside of its closed distribution area, the rough owl is mainly tied to low mountain range and mountain forests, but is also increasingly spreading in lowland areas in the east and north. The ridgway owl only occurs at altitudes above 1400 meters and breeds at altitudes of over 3000 meters; The distribution areas of the yellow-faced owl, of which breeding sites are already known from altitudes around 600, but which can also be found in populations of Polylepis called queñuales, are less exclusively in mining regions .
Food and subsistence
Owls of the genus Aegolius feed mainly on small mammals. In addition, small birds play a certain role, with the ridgway and yellow-faced owls arthropods , especially insects , are likely to dominate. Among the mammals, voles , shrews and moles , and among birds, different types of passerine birds make up the main prey. The food composition of the two Neotropical species is largely unknown, but frogs and bats, along with insects, small mammals and birds, could be important prey. The subspecies of the saw owl A. a. Breeding on Haida Gwaii . brooksi also frequently prey on crabs and other crustaceans .
All species of this genus are mainly high seat hunters who locate their prey either acoustically or visually and hit the ground after a hover. The barn owl can reliably locate a moving mouse acoustically from a distance of 23 meters. Occasionally he shakes the suspected prey. The control room is usually changed after each prey flight. In addition, air hunting has to play a certain role, but was hardly observed. The prey animals are killed by a bite in the head or by firm clawing and are eaten piece by piece; Birds are plucked.
The rough owl and the gray owl create extensive food depots during winter and during the breeding season. Nothing is known about the other two species.
behavior
All species of this genus are largely nocturnal. The activity phase begins at late dusk and ends well before sunrise. Even during the breeding season, the day is spent resting, usually sitting on a branch close to the trunk. Only in exceptional cases were individuals of the rough owl living to the north found hunting even on cloudy days. At least the males are territorial throughout the year, but essentially only a small territory seems to be actually defended against conspecifics.
The two neotropical species are resident birds. With them, only irregular, climatic compensatory movements seem to take place. The males of the barnacle owl are also largely loyal to their place, while the females pass more often and make migratory movements of around 500 kilometers. European pullers regularly cross the Baltic Sea . The gray owl is largely a short- or medium-distance migrant, at least in its northern populations, which can migrate to the south for over a few thousand kilometers. For example, many owls that breed in central Ontario pass to Kentucky, or birds from Nova Scotia to North Carolina . Saw owls have been observed in Florida and Mississippi during the winter .
Breeding biology
Owls of this genus become sexually mature at the end of their first year of life. You have a breeding season partnership. Both polyandry and polygyny are not uncommon. The pair bond expires at the latest after breeding, often already in the branching stage of the young birds. In such a case the female starts a new brood with a new partner. On the other hand, in good feeding years, a male can breed with two females at the same time.
All four species are cave-breeders, which are mainly dependent on caves of larger woodpecker species such as the helmeted woodpecker or black woodpecker. In addition, natural tree hollows and, in the case of the rough owl and the saw owl, nest boxes are also used as breeding grounds. A brood of the yellow-faced owl in a rotten palm stump is known. Nesting material is not entered, and the bulges, the excretions of the young birds, as well as feathers and other plucking remains remain in the nest.
The clutches of the well-studied rough-owl and saw-owl are mostly large. They consist of up to seven white eggs. Occasionally several females are allowed to lay in a nest, so that giant clutches of over 10 eggs can arise. The eggs are laid every day, often every two days, and incubated from the first egg on, so that there are very large differences in development among the nestlings.
The female breeds alone. The breeding period for all species is around 28 days. During this and the following wet season , the male provides the females and chicks with food. If the food supply is poor, it often happens that the stronger boys kill and devour the weaker stragglers. After the young have left the nest at around 28 days, the female also takes part in the foraging; however, it often leaves the brood and starts a new one, sometimes quite far away. The young cannot fly at this time. When they fall to the ground, they try to hide in the undergrowth or use their claws and beak to get back to safer heights. Only after another 4–6 weeks are they independent and leave the breeding area.
Although the rough owl and the sawtooth owl occur sympatricly in large parts of their distribution area in North America, no mixed broods between these two species have been known to date. Between the saw owl and the Ridgway owl, on the other hand, there are likely to be mixed broods whose offspring are sometimes listed as subspecies of the Ridgway owl.
There is hardly any information on the breeding biology of the other two species.
Life expectancy
Little information is available on the life expectancy of the rough owl and the saw owl. A ringed owl was found after 10 years and 2 months. Another survived over 16 years in captivity.
Significantly more than half of all young birds die before reaching sexual maturity. Reasons for this are deficiency situations during rearing, parasitic diseases, predation by larger owls and martens and accidents of the young birds, which are still insecure to fly. A large study in the USA showed that saw owls are disproportionately often victims of road traffic. Almost 80 percent of the birds killed were younger than a year.
Systematics
The four recent Aegolius species form a monophyletic genus that is genetically and behaviorally well separated from other genera within the subfamily of the surniinae, which underlines their monotypical position in the tribe Aegolini. They are closely related to the genera Glaucidium , Umgebung, and Athene . The saw owl and ridway owl are considered by some researchers as a polytype species.
| German name | Scientific name | distribution | Hazard level Red List of IUCN |
Remarks | image |
|---|---|---|---|---|---|
| Little Owl |
Aegolius funereus ( Linnaeus , 1758) |
boreal forest belt of the northern Holarctic Central Europe, Pyrenees, Caucasus |
 ( Least Concern - not at risk)
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5 subspecies at König & Weick; for other authors up to 8. |
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| Saw owl |
Aegolius acadicus ( Gmelin , 1788) |
Southern Canada; NE and N-USA W-USA southwards to southern Mexico |
( Least Concern - not at risk)
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2 subspecies in König & Weick; with other authors 3. |
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| Ridgway Owl |
Aegolius ridgwayi ( Alfaro , 1905) |
S-Mexico to Panama |
( Least Concern - not at risk)
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according to König & Weick, there are often 2 monotypical subspecies which König & Weick consider to be hybrids of A. ridgway × A. acadicus . |
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| Yellow-fronted Owl |
Aegolius harrisii ( Cassin , 1849) |
Eastern slope of the Andes from Venezuela to Bolivia SE Brazil, La Plata area |
( Least Concern - not at risk)
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3 subspecies |
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In 2012, Storrs Lovejoy Olson described the subfossil remains of an extinct Aegolius species from Bermuda . Aegolius martae is known from the Pleistocene , which occurred in Sicily and was described by Marco Pavia in 2008.
| German name | Scientific name | distribution | Hazard level Red List of IUCN |
Remarks |
|---|---|---|---|---|
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Aegolius gradyi Olson , 2012 |
Bermuda |
 ( Extinct - extinct)
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known only from subfossil remains | |
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Aegolius martae Pavia , 2008 |
Sicily | Extinct in the Pleistocene |
Stock situation
The IUCN does not list any species in a hazard level. However, there are practically no population analyzes for the ridgway owl and the yellow-faced owl. The owl, like other owls, is likely to be overlooked due to its hidden way of life and its sometimes remote breeding areas. Its population is estimated at 100,000–300,000 individuals. The rough owl is also one of the more common owls in its range. As the increase in lowland broods shows, the core areas seem to be under considerable pressure to spread. In addition, both the species and the owl benefit from the addition of nesting boxes.
In addition to the natural population-limiting factors, deforestation and pest control, but also cave competition from introduced species such as the starling, have a not inconsiderable population-minimizing effect.
literature
- Urs N. Glutz von Blotzheim (Hrsg.): Handbook of the birds of Central Europe . Volume 9: Columbiformes - Piciformes. 2nd Edition. Aula-Verlag, Wiesbaden 1994, ISBN 3-89104-562-X .
- James R. Duncan: Owls of the World . Firefly Books, Buffalo 2003, ISBN 1-55297-845-1 .
- Jochen Hölzinger , Ulrich Mahler: The birds of Baden-Württemberg. Non-singing birds. Volume 3, Ulmer, Stuttgart 2001, ISBN 3-8001-3908-1 .
- Claus König, Friedhelm Weick: Owls of the World . Christopher Helm, London 2008, ISBN 978-0-7136-6548-2 .
- Theodor Mebs : Owls and Owls . Kosmos, Stuttgart 1987, ISBN 3-440-05708-9 .
- Justin Lee Rasmussen, Spencer G. Sealy, Richard J. Cannings: Northern Saw-whet Owl (Aegolius acadicus) . In: A. Poole (Ed.): The Birds of North America Online. Cornell Lab of Ornithology, Ithaca 2008. Retrieved from the Birds of North America Online.
- Viktor Wember: The names of the birds of Europe . AULA, Wiebelsheim 2005, ISBN 3-89104-678-2 .
Individual evidence
- ^ Search for "Aegolius" in the IUCN Red List of Threatened Species . Retrieved November 10, 2009.
- ↑ Wember (2005) p. 109.
- ↑ a b König & Weick (2008) pp. 441–448.
- ↑ HBV Vol. 9 (1980) p. 532.
- ↑ a b König & Weick (2008) pp. 443 and 445
- ↑ König & Weick (2008) p. 445.
- ↑ HBV Vol. 9 (1980) p. 567.
- ↑ a b König & Weick (2008) p. 444.
- ↑ König & Weick (2008) p. 447.
- ↑ Rasmussen et al. (2008) Demography
- ^ Rasmussen et al. (2008) Lifespan
- ↑ König & Weick (2008) p. 48.
- ↑ Rasmussen et al. (2008) Systematics
- ↑ Storrs L. Olson: A new species of small owl of the genus Aegolius (Aves: Strigidae) from Quaternary deposits on Bermuda In: Proceedings of the Biological Society of Washington: Vol. 125 (2), 2012, pp. 97-105
- ↑ Marco Pavia: The evolution dynamics of the Strigiformes in the Mediterranean islands with the description of Aegolius martae n. Sp. (Aves, Strigidae) In: Quaternary International: Vol 182 (1), 2008, pp. 80-89
- ↑ König & Weick (2008) p. 446.
