Saw owl
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Saw owl ( Aegolius acadicus ) |
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| Scientific name | ||||||||||
| Aegolius acadicus | ||||||||||
| ( Gmelin , 1788) |
The Saw Whet Owl ( Aegolius acadicus ) is a small North American Art from the family of owls (Strigidae) that the slightly larger boreal owl is quite similar. Its name comes from the fact that its calls supposedly sound like sharpening a saw with a whetstone.
The distribution area of the owl extends through the boreal and cool temperate zone from south Alaska eastwards to Nova Scotia and in the mountains in western North America in fairly fragmented occurrences southwards to Mexico . The species is a partial migrant , with northern populations in particular moving south in autumn.
The saw owl breeds mainly in mixed forests , but can also be found in many other forest forms and trees. It is important to have a good supply of nesting holes and sleeping trees. It is a hide hunter that feeds mainly on small rodents. Shellfish and aquatic insects are often prey on the Pacific coast.
description
The saw owl is a small owl that is somewhere between the little owl and the pygmy owl . Males reach body lengths between 18 and 20 cm, females are slightly larger with 20–21 cm. The weight is between 75 and 100 g. Like the closely related barn owl , the legs and toes are densely feathered. The head is relatively large and does not have feather ears . The iris is yellow to golden yellow. The wings are clearly rounded with 10 hand wings; the tail is short.
In adult birds the color of the upper side is brown with strong, white dots on the forehead, crown and neck, which condense like a seam around the face veil. The round face veil is white between and above the eyes - that is, below the V-shaped forehead protruding into the veil - and brown and white dashed towards the edge on a light brown background. Shoulder feathers and wing coverts show a whitish, teardrop-shaped speckle, which is also present at the edge on part of the wings. The control springs are relatively narrow and banded at a large distance. The underside is broadly reddish brown to brown, longitudinally striped on a white background.
Birds in youthful dress are relatively dark brown on top with beige spots on the shoulders and whitish spots on the wing and control feathers. The chest is brown and the rest of the underside is cinnamon. The white area between and above the eyes looks Y-shaped and stands out clearly from the black-brown face veil. The plumage on the chin is beige.
voice
The Northern Saw-whet Owl got its name from the fact that its call supposedly sounds like sharpening a saw blade with a whetstone. Opinions differ as to which of the numerous vocalizations of the species it is.
The singing is a monotonous series of calls made of softly fluting sounds of the same pitch, which are repeated at very short intervals. It carries about 300 m within forests, it can be heard about 1 km away over water. The singing is mostly performed by the male, but can also be heard by the female. When arriving at the nest, before copulation or as an introductory element of the song, the male can sometimes hear a series of calls that is similar to the song, faster, deeper and consisting of only 4-5 elements. In response to the nest or when mating, the female expresses a high and distinctive tssst .
The excitement call is a high-pitched, drawn-out, cat-like "crying" as well as - mostly probably with intruders in the area - a sharp, high- pitched staccato-like "barking". Squeaking, guttural gurgling and screeching sounds are also described.
The begging call of the nestlings is a 6- to 8-syllable chirping. At the time of fledgling, this becomes a rougher chsk .
distribution
The owl inhabits the boreal and cool-temperate deciduous forest zone from the Alaska Peninsula and southeastern Alaska southwards via British Columbia (where the species is also found on Haida Gwaii and Vancouver Island ), Washington , Oregon , Montana , Wyoming and to the southern foothills of the Rocky Mountains in Colorado . Eastward, the distribution extends through temperate Canada to Nova Scotia . In the south, the distribution extends there to the south of the Great Lakes and along the highest peaks of the Appalachians to Kentucky , Virginia , North Carolina and Tennessee .
The species is absent in the south-east of North America and the Great Plains . In the west and south-west it occurs mainly in mountains and is found there in several disjoint sub-areas along the Cascade Range , the Sierra Nevada and the Sierra Madre Mountains and south to Oaxaca in Mexico .
Geographic variation
Two subspecies are recognized, of which brooksi is smaller, darker and more long-tailed than the nominate form . In addition, the white base color of the underside and the white spots on the wings are tinted yellowish beige. In the case of acadius in eastern North America, there is a slight increase in size towards the north. Birds from the southern Appalachians, which are believed to be a disjoint population, are, like brooksi, significantly smaller.
- A. a. acadicus ( JF Gmelin , 1788) - entire distribution area except Haida Gwaii
- A. a. brooksi ( Fleming , 1916) - Haida Gwaii
hikes
The gray owl is a partial migrant in which the populations of southern Canada in particular migrate south in autumn, but many birds in the east and west of North America are resident birds . The brooksi subspecies is one of the latter. In the mountains, migration from higher elevations can often be seen in winter.
The wintering areas of the migratory birds extend south to Iowa, Indiana and New Jersey, more rarely are overwintering in Oklahoma, Kansas, Virginia or Tennessee, Louisiana, Georgia, Nevada, in southern California or in Arizona. However, wanderers also reach the Gulf of Mexico . The train movements in autumn take place mainly in the months of September to November, the train peak is in October. The spring migration is completed by the end of May or by the beginning of June at the latest.
In some years with good breeding success - on average every four years - the number of migrating individuals is particularly large. For example, in 1995 2596 saw owls were caught at five ringing stations on the Atlantic coast, while in the previous three years only around 200 specimens of this species were found at four of these stations per year. The proportion of this year's individuals then seems to predominate.
habitat
The saw owl occurs as a breeding bird in a wide range of forest forms and trees. Obviously, the presence of nesting holes, leafy deciduous trees or conifers that can serve as sleeping places and a good food supply for small mammals are decisive. The species reaches particularly high population densities in coniferous forests along rivers, but can also be found in mixed forests, deciduous forests, coniferous forests and shrub savannas with trees. Where suitable nesting boxes are available, the saw owl also breeds in coastal bushes, in dune vegetation and in poplar trees. In California, the species also takes on eucalyptus groves. Nesting holes have also been found in dead conifers within forest bogs or in a mast along a swath through a forest of Banks pine .
The preferences are evidently very different locally. While coniferous forests are preferred in some places, the species is particularly common in deciduous forests elsewhere. Height differences, age and species composition of the forests and the proximity to other (e.g. open) habitats only play a regional role. In the wintering areas, the occupied habitat types also vary greatly. Presumably, the presence of suitable sleeping trees plays a role here.
Reproduction
The males' chant of the territory can be heard from late January to May. During this time, the females also arrive in the territories. Some areas are not open until the beginning of the year, others are probably occupied all year round.
The saw owl breeds in existing nesting holes where the entrance is between 6 and 9 cm wide, the inside diameter is between 7.5 and 9 cm and the depth is between 22 and 45 cm. The species is therefore mostly dependent on the nesting holes of golden and helmeted woodpeckers. Sometimes caves of smaller woodpecker species such as the hairpecker caused by rotting or by rotting or enlarged by croissants are also suitable. Nest boxes of the right size - such as those for the wood duck - are also accepted. Nesting material is not entered. The eggs are laid on the found floor of the cave, for example in the rotting wood or on old nesting material from the previous residents.
Laying begins between February and the beginning of June, with different regional times. Broods that started in June and July are probably only secondary eggs and second broods. However, the latter have only been observed in captivity so far. The clutch consists of 3–7 white, round oval eggs with a slightly shiny to matt surface and a size of about 25 × 30 mm. Incubation begins with the first or second egg and lasts between 27 and 29 days. It is done exclusively by the female, who only leaves the nest for one or two short flights at night and is fed by the male.
After hatching, the young are still at least 18 days brooded . During this time the young and the female are fed by the male. After that, the female takes part in the rearing of the young or completely removes itself from the nesting site. During the Huder period bulges and excrement are removed from the female, later these accumulate in the nest cavity and sometimes form a layer several centimeters thick.
After leaving the nest box, the young stay near the nest box and are fed for about a month. They are likely to be self-employed after six to eight weeks, but this is not exactly known.
supporting documents
- Richard J. Cannings: Northern Saw-whet Owl in The Birds of North America Online , accessed September 19, 2011
- DA Sibley: The Sibley Field Guide to Birds of Eastern North America , AA Knopf, New York 2003, ISBN 0-679-45120-X
Individual evidence
- ↑ Sawtooth ( audio sample ; MP3; 638 kB)
- ↑ DF Brinker, KE Duffy, DM Whalen, BD Watts and KM Dodge: Autumn migration of northern saw-whet owls (Aegolius acadicus) in the middle atlantic and northeastern united states: What observations from 1995 suggest in Biology and Conservation of Owls of the Northern Hemisphere (1997), pp. 74-89, cited in Bird of North America Online (see evidence)
Web links
- Aegolius acadicus in the endangered Red List species the IUCN 2008. Posted by: BirdLife International, 2008. Accessed January 31 of 2009.
- Videos, photos and sound recordings on Aegolius acadicus in the Internet Bird Collection
- xeno-canto: sound recordings - Northern Saw-whet Owl ( Aegolius acadicus )