Long-eared owl
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Long-eared owl | |
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A long-eared owl in Hungary | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Chordata |
Class: | Aves |
Order: | Strigiformes |
Family: | Strigidae |
Genus: | Asio |
Species: | A. otus
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Binomial name | |
Asio otus | |
Range of A. otus Breeding Resident Non-breeding Extant (seasonality uncertain)
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Synonyms | |
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The long-eared owl (Asio otus), also known as the northern long-eared owl
This owl shows a partiality for semi-open habitats, particularly
Taxonomy
The long-eared owl was formally described by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae under the binomial name Strix otus.[19] This owl is now assigned to the genus Asio that was introduced by the French zoologist Mathurin Jacques Brisson in 1760.[20][21]
Owls in the genus Asio are sometimes commonly referred to as eared owls. Despite their extensive distribution, only eight modern species are thought to exist. Four species are found both in
Subspecies
Four subspecies of the long-eared owl are recognised:[21][30][31]
- A. o. otus (cere is brownish-flesh, the bill is grey and the talons are blackish-grey. In this subspecies, the downy chick is whitish with pink skin, while the mesoptile plumage is fluffy greyish to brownish-white with diffusely barred dusky flight and tail feathers, being similar to adults but with the ear-tufts not yet developed.[4][8][32]
- A. o. canariensis (endemic to the Canary Islands. With a wing chord measurement of 257 to 284 mm (10.1 to 11.2 in), this is seemingly the smallest subspecies of the long-eared owl.[4][8] This race averages darker than most long-eared owls of the nominate subspecies, bearing heavier and sharper dark markings overall. Furthermore, the Canary Island long-eared owls tend to have brighter reddish-orange eyes.[4][8][33]
- A. o. wilsonianus (Lesson, 1830) – This subspecies is found in south-central and southeastern Canada (Manitoba to Nova Scotia) to southern USA (north Oklahoma and Virginia).[4][8] The wing chord typically measures 284 to 305 mm (11.2 to 12.0 in). In general, American long-eared owls are more vividly marked than many Eurasian populations. The facial disc is bright rufous, with a strong blackish rim and extensive white about the disc. The eyes are typically a deep yellow. Meanwhile, the markings on the underside usually are quite blackish and prominent with distinct cross-bars.
- A. o. tuftsi Godfrey, 1948 – The range is from western Canada (southern Yukon to southwest Manitoba) to south-central USA (west Texas). It differs from A. o. wilsonianus in having paler plumage. The brown mottling on upper parts is paler and more restricted.[34] It is weakly differentiated and may comprise clinal variations due to region and habitat, rather than subspecific differences.[8][32][25]
Description
This species is a rather slim and long winged owl with usually prominent erectile ear tufts, which are positioned closer to the center of the head than in many other types of owl. The purposes of ear tufts are not definitively known and are present in about half of living owls.
The long-eared owl is a medium-sized owl, which measures between 31 and 40 cm (12 and 16 in) in total length.
In standard measurements, long-eared owls vary in wing chord length from 262 to 315 mm (10.3 to 12.4 in) in males, with 883 in North America averaging 285.1 mm (11.22 in), and 255 to 332 mm (10.0 to 13.1 in) in females, with 520 American ones averaging 286.2 mm (11.27 in). The tail may measure 121.5 to 161 mm (4.78 to 6.34 in) in males and 143.5 to 165 mm (5.65 to 6.50 in) in females, with 1,408 owls averaging 146.3 mm (5.76 in).[8][9][32][47] Less widely measured are bill length, which averaged 15.7 mm (0.62 in) in males and 16.2 mm (0.64 in) in females from North America, and tarsus length, which averaged 38.2 mm (1.50 in) in 20 males and 39.9 mm (1.57 in) for 16 females from Europe, with a range in both sexes of 36.9 to 42.3 mm (1.45 to 1.67 in).[46][48][49] In terms of their skeletal structure, it bears a relatively wide skull but relatively small eyes and orbits, while the beak is relatively elongated but weak.[4][47] The legs are relatively long and thin and, while needle-sharp, the talons are relatively fine and the feet relatively weak for an owl. However, the talons are still highly proficient at drawing blood if contact is made with human skin.[4][47][50][51]
Identification
If seen well, an experienced observer is usually able to distinguish a long-eared owl by combination of its field marks, size and coloration. However, some potential owl species may be confused for them. The
Over much of its range, long-eared owls occur with the related
Vocalizations and ear morphology
The long-eared owl has relatively large
The vocalizations of this species are highly variable. Amongst owls of all ages, long-eared owls in
Distribution and habitat
The long-eared owl has an extremely large distributional range. In
This species is found widely distributed in North America as well. Their northern limits are reached in much of
Habitat
Optimal habitat tends towards access to open spaces with short vegetation and abundant prey and wooded cover for roosting and nesting.
Behaviour
Long-eared owls are more or less strictly nocturnal in activity. Usually activity for the species commences at dusk.
Migration
Out of roughly 19 regular species of owl in
The long-eared owl has the peculiar ability to increase populations and then disperse in nearly multi-directional movements during good years for prey numbers. Banding records across North America show highly erratic numbers and movements across the continent of North America with unpredictable peak numbers of migrants in completely different years respectively for the states of Wisconsin, Michigan, New York and New Jersey.[100] Therefore, the species is sometimes considered “nomadic” despite many populations of the species being consistent annual migrants. Similar tendency towards so-called “nomadism” is shared by other widespread raptors semi-specialized to hunting voles over open ground, such as short-eared owls and hen harriers (Circus cyaneus).[4][18][100] These erratic movements and peaks and ebbs of northern populations has lent to descriptions of the long-eared owl as “irruptive”, however it generally moves in quite different ways from owls largely endemic to the taiga (or tundra), which are more traditionally irruptive in that they tend to migrate little or not at all when prey remain ample in their native home range but then move south in mass when prey populations crash. Long-eared owls, unlike these irruptive northern owls, often migrate from the northern areas regardless of conditions. However, like the northern irruptive owls, long-eared owls tend to appear in unprecedented numbers to the south when a peak prey year is followed by a winter during which prey population crashes. In North America, the migratory habits of long-eared owls are strongly mirrored by those of northern saw-whet owls.[18][101][102] Study of banding records in Saskatchewan show that the long-eared owl Canadian populations may be considered more truly irruptive species both as a breeder and migrant in that only appears in numbers during peak vole years, with large numbers only in 4 of 44 banding years. During 7 low years, the long-eared owls of Saskatchewan seemed to disappear altogether from much of the province. Peak years also coincided often with snowshoe hare (Lepus americanus) peaks, possibly due to lessened competition (as the larger owls favored prey is locally the hare) and interspecific predation by great horned owls.[15][100] The phenomena of movements that seem to be nomadic or purportedly irruptive in nature may occur as well in Europe, though given the species' denser population in general there in comparison to North America may result in less noticeable wide variations in numbers.[4][37] Years with irruptive numbers of long-eared owls have been noted in the British Isles when prey peaks then crashes back in Scandinavia, resulting in much larger numbers of migrant long-eared owls into the islands than normal, as well as concurrently large numbers of short-eared owls and harriers.[14][103] In southern Finland during a peak prey year followed by a prey crash, a very large number of long-eared owls were detected and were seen to be likely food stressed, as several were foraging actively during daylight despite the extensive nighttime hours during the season.[104]
Social and roosting behavior
During daytime, long-eared owls tends to roost in an upright position on a branch, not infrequently close to the trunk, oftentimes within dense foliage. In winter, the long-eared owl often stays close to the same tree or grove of trees (i.e. in and around parks, large gardens, or cemeteries). Usually, when approached, the owl freezes with its body stiffly upright, eyes closed to narrow slits and ear tufts erect. This is called the “tall-thin position” and is common to at least a couple dozen species of typical owl. If approached closed, the owls will alternately open and close their eyes (apparently having stirred but trying to fool potential predators into thinking the owl is still at rest), finally lowering ear tufts, fluffing body plumage and flying to another roost.
Dietary biology
Long-eared owls may divide their hunting into phases, the first stopping around midnight, the second beginning some point after midnight and ending an hour before sunrise.[4][8] While hunting, they tend focuses on the edge of woodlands, hedgerows and open spaces with rough grassland, and over young trees and open ground of all kinds. They hunt mainly on the wing, flying low and fairly slowly, often being quite low to ground, i.e. only around 150 cm (59 in).[4][8][36] More often than visually finding their prey, it is thought that long-eared owls most often audibly detect the rustling of their intended food. In lab settings, long-eared owls were considerably more skilled at finding mice by sound in more or less complete darkness than tawny and barred owls (Strix varia), and in some American experiments even outclassed the auditorily-acute barn owls in this regard.[108][109] Once prey is spotted, the long-eared owl's flight suddenly stalls, then they quickly drop with talons spread to pounce on prey that is perceived, or especially, that comes out into the open.[4][8] Habitat may be perhaps even more key than prey numbers to the selection of hunting grounds. Often when prey numbers are more ample in timbered areas nearer the roost or rich marshy areas in the vicinity, the long-eared owls will still often come to more prey-poor areas such as old fields so that they can detect prey on open ground.[80][110] The footspan of a long-eared owl, including claws, reaches on average 11.3 and 12.5 cm (4.4 and 4.9 in) in males and females, respectively, which would be large for a diurnal bird of prey but is quite small for an owl of its size, given the physiological differences in the way different birds of prey tend to kill their prey. While acciptrid raptors tend to kill by stabbing with their talons through vital organs, owls are more likely to constrict their prey to death, so tend to have proportionately larger, more robust feet.[4][108][111][112] In other medium-sized owls, the footspan in tawny owls and barn owls respectively averages 13.4 and 13.2 cm (5.3 and 5.2 in) in between the sexes (notably footspan seems to be a fairly reliable predictor of body mass of an owl as well).[4][108] Prey capture by long-eared owls was studied and compared to tawny owls in a European experiment. The two owl species caught mammals and beetles caught in similar ways but the long-eared owls shied away from flying sparrows and would only capture the sparrows when they perched (though the tawny did not avoid flying sparrows, it too would only capture the prey when perched). Long-eared owls either disregarded or killed but did not eat amphibians, while tawny owls did catch and eat amphibians when they were available. Occasionally the tawny owls would attack fish whilst one long-eared owl caught but did not eat a fish. The European study further revealed that several owls of different species ate bits of plant and did not appear to do so out of food deprivation or hunger.[113]
Taken as whole, the global population of long-eared owls may appear to have a widely varying diet. One study accrued information from 312 studies from around the species' range. In total 478 prey species were found to be described, of which 180 were mammal species, 191 were bird species, 83 were assorted invertebrate species, 15 were reptiles, 7 were amphibians, and reportedly just a couple fish species. This included a total of approximately 813,033 prey items having been reviewed.[114] However, on closer inspection, the long-eared owl generally appears to be something of a dietary specialist. It usually takes primarily, often nearly entirely, small mammals, e.g. rodents, as food in almost every part of its range. Usually a broad picture emerges that between 80 and 99% of the diet consists of mammals, averaging 94% in one estimate for all of Europe. However, in warmer, insular or more urbanized environments, a greater percentage or, rarely, even a majority of the diet can locally be non-mammalian prey.[4][8][114][115] Mean prey sizes have been studied extensively and are almost always fall within a very narrow range. In Europe, the mean estimated prey size overall was 32.2 g (1.14 oz).[48][115] Meanwhile, in North America, mean prey sizes have varied between 30.7 and 37 g (1.08 and 1.31 oz) in two estimates.[108][115] In general, throughout their range, the mean size of prey is generally encapsulated between 20 and 50 g (0.71 and 1.76 oz), usually well under 40 g (1.4 oz), and only in cases where long-eared owls, perhaps through lessened competition, has regular access to prey weighing 60 to 100 g (2.1 to 3.5 oz) or more, may the mean prey size range uncommonly reach 50 to 60 g (1.8 to 2.1 oz).[108][114][115] Cases of exceptionally large prey are mentioned where they occur below.
Mammals
The long-eared owls derives almost of its food energy from
In some parts of Europe, common voles are at times not found or are locally infrequent or rare, especially on large islands,
Outside of Europe within Eurasia, the feeding association with voles for long-eared owls weakens somewhat but does continue apiece in adjacent
In North America, long-eared owls also primarily rely on small rodents in their diet, but their diet is somewhat more diverse by rodent family and less completely reliant on voles than their Eurasian counterparts.
In many areas, particular arid vicinities, the
Non-rodent mammalian prey is seldom of great import to long-eared owls, though they can take some numbers of other kinds of mammals locally. Despite claims that the long-eared owls “avoids” shrews as prey, it is probably more correct to say that they do not seek them out nearly as often as more socially inclined and/or densely populated rodent prey. Some other owls may be considered regular and common shrew predators, such as often barn owls. In Europe, a broad picture of prey selection indicates about 2% of the diet of long-eared owls consists of shrews.[4][48][115] Locally, relatively high numbers of shrews were reported in Finland, where 10.7% of 3,759 prey items were common shrews (Sorex araneus), in southern Scotland, where the common shrew made up 17.3% of 514 prey items, in northeast Greece, where lesser white-toothed shrew (Crocidura suaveolens) were 19.3% of 311 prey items and in western Siberia, where Sorex species were 17.3% of 335 prey items.[12][127][138][148] Similarly, in North America, shrews are rarely more than secondary prey.[115] Exceptionally high numbers of shrews were noted in Ohio, where the relatively large northern short-tailed shrew (Blarina brevicauda) and the relatively small North American least shrew (Cryptotis parva) made up 10.46% and 10.22% of the diet, respectively, and in Tennessee, where 12.85% of the diet was least shrew.[156][173] The smallest mammal on earth (and thus smallest recorded mammalian or vertebrate prey), the 1.8 g (0.063 oz) Etruscan shrew (Suncus etruscus), may be seldom hunted by long-eared owls.[176] Bats are another supplemental prey type for long-eared owls. One compilation study based on 12 study sites in the Mediterranean area (in Spain, Italy, Greece, Slovenia, Romania and Switzerland) found up to 2% of prey remains were bats. The bats taken in the Mediterranean region ranged in size from the whiskered bat (Myotis mystacinus), estimated at as low as 4 g (0.14 oz), to the European free-tailed bat (Tadarida teniotis), estimated to weigh up to 54 g (1.9 oz).[177] A exceptionally close predatory relationship was noted between bats, especially Japanese house bats (Pipistrellus abramus), and long-eared owls in the Beijing area of China, where bats accounted for 28.6% of 3,561 prey items overall, and 56.6% of the diet locally in urban, rather than suburban, roosts.[178] Other mammals, outside of aforementioned groups (i.e. cricetid, murid and geomyoid) rodents, are known to be hunted but are generally a negligible part of the long-eared owl's diet, including hedgehogs, moles, rabbits and hares and weasels as well as rarely taken rodents like dormice, flying squirrels and squirrels (including chipmunks).[4][114][115][121][131][147] While lagomorphs such as hares and rabbits are very rare prey for long-eared owls, occasionally they may capture one. Such prey was estimated to weigh 271 g (9.6 oz) (for cottontail rabbits) and 471 g (1.038 lb) (for jackrabbits) in Idaho, meaning very small young rabbits and jackrabbits are likely captured.[167][169][170][174] However, sometimes long-eared owls can very rarely capture exceptionally large lagomorphs. The record sized mammalian prey to be taken by a long-eared owl, was recorded in the case of predation upon a probable juvenile black-tailed jackrabbit (Lepus californicus) which weighed an estimated 800 g (1.8 lb).[115] Two instances of scavenging on carrion were reported in Italy, the first known case of this for the species, where long-eared owls consumed parts of an adult crested porcupine (Hystrix cristata) and an adult European pine marten (Martes martes), both prey the long-eared owls were certainly unlikely to have killed.[179]
Birds
Long-eared owls are generally infrequent predators of birds. Food studies from Eurasia place it as an opportunistic and occasional bird predator, while in North America they are do not seem to generally take large numbers of birds in any area. In winter, sometimes these owls can come to live largely off of small birds gathered in communal sleeping places, often near villages or towns. Particularly
Many Italian studies reflect relatively high numbers of birds being hunted, mainly in the non-breeding times. One of the smaller large representations was at
While most of the passerines attacked by long-eared owls are well within typical prey sizes for this species, while pursuing bird prey many reports note that unusually large prey may be attacked. Avian prey weighing around 100 g (3.5 oz) or somewhat higher such as the larger common
Other prey
Other than mammals, which compromise a great majority of foods, and birds, which compromise a secondary but locally important portion of the foods, other prey varieties are seldom taken by long-eared owls anywhere. Infrequently,
Interspecies predatory relationships
The long-eared owl occurs in multiple competitive environments of the temperate zone alongside other
On a broader scale, both
North America has more species of owl than Europe and can be considered a more competitive environment for long-eared owls living there. However, again, in most cases habitat preferences, slight partitioning in dietary preferences (which may be in prey species or body sizes of prey selected) and life histories generally allow most species to persist even when living in proximity to one another.[4][9] As throughout their range, long-eared owls tend to differ from most other North American owls by being much more migratory in nature. Therefore, cyclic food variations affect them differently and are less likely to be the direct cause of winter mortality than in more permanently residential owls.[32][101][222] Oddly enough, among American owls, long-eared owls most strongly mirror the much smaller northern saw-whet owl in distribution, migratory habits and, to a lesser extent, food habits. The main food of saw-whet owls tends to be Peromyscus mice where they are available and, like most owls, their rodent food selection can broadly overlap with that of long-eared owls.[97][98][115][156] It has been posited that the less broadly ranging occurrence of long-eared owls in general compared to in their European range is in part due to greater resource competition between them and the two widespread screech owls, the eastern (Megascops asio) and western screech owls (Megascops kennicotti).[4] However, the feeding niche tends to be much wider and more opportunistic in screech owls, which often feed on a diversity of invertebrates (mainly insects but also crayfish) and alternate prey (a higher balance of birds and frogs, for instance) and so are unlikely to competitively limit rodent numbers to the detriment of long-eared owls.[9][32][115][170]
The most easily observed and most dramatic portion of interspecies owl and raptor ecology is interspecific predations. In this regard, long-eared owls are much more often the victims rather than the predators. Their generally successful life history on the contrary often makes long-eared owls perhaps more vulnerable than most other medium-sized owls to predations and even perhaps many smaller owl species. These include nesting in relatively open abandoned bird nests rather than hard to access cavities. Also, long-eared owls tendency to occur in quite open areas whilst hunting coupled with the loud vocalizations (including begging calls of their fledglings) and other auditory displays are all likely to court predators.[4][37][41][79][223] In Europe, their most serious predators tend to be the Eurasian eagle-owl and the northern goshawk (Accipiter gentilis). One account recorded 768 instances of predation by eagle-owls and 317 by goshawks (or 55% of the owl prey for recorded for goshawks in Europe).[4][37][79] Long-eared owls rank in the five most regular predated bird species by eagle-owls in Europe.[79][224][225] Some biologists feel that long-eared owls tendency to avoid richer prey concentrations in favor of opener habitats and spatial usage, especially while migrating and wintering, is partial dictated by the detection of eagle-owl (and perhaps goshawk) activity, so therefore the eagle-owl has a serious influence on the long-eared owl's life history.[4][36][43] In general, long-eared owls endure predation by a formidable array of diurnal birds of prey in Europe. It is likely that largely perch hunting raptor such as Buteo and most eagles may either chance upon an owl roost during a hunting foray or encounter a long-eared owl perhaps during overlapping activity around dawn or dusk, while large falcons are likely to only strike one down when an owl is flushed during daytime. Goshawks and other Accipiter hawks are a particularly deadly threat among diurnal raptors due to their intensive searching hunting methods and willingness to dive into wooded thickets holding roosting owls.[37][79][226][227] Beyond goshawks, diurnal raptors in Europe known to be predators of long-eared owls of potentially any age are known to include golden eagle (Aquila chrysaetos), Bonelli's eagle (Aquila fasciata), eastern imperial eagle (Aquila heliaca), greater spotted eagle (Clanga clanga), lesser spotted eagle (Clanga pomarina), black kite (Milvus migrans), red kite (Milvus milvus), white-tailed eagle (Haliaeetus albicilla), common buzzard, rough-legged buzzard (Buteo lagopus), peregrine falcon (Falco peregrinus), saker falcon (Falco cherrug) and even (in two cases) the slightly smaller Eurasian sparrowhawk (Accipiter nisus).[4][79][228][229][230][231][232][233][234] Other than eagle-owls, tawny owls and Ural owls (Strix uralensis) regularly kill long-eared owls where their ranges meet, though in some cases these may begin as territorial attacks by the Strix owls, the smaller long-eared may be consumed regardless.[4][79]
In North America, the range of predators of long-eared owls is no less daunting. Undoubtedly the most dangerous American predator is the
Breeding
Long-eared owls tend to be monogamous breeders. Non-migratory populations are usually monogamous throughout the year, the pair bond being renewed annually.[8][36] A study in Idaho determined that long-eared owls were locally extremely monogamous, with no extra-pair fertilizations were detected in 59 nestlings from 12 nests.[245] There is a single record of a male breeding with 2 females in Netherlands, a very atypical case.[8] Similarly, evidence of polyandry and alloparenting was found in a nest in western Montana where the four offspring of the female owl had two fathers, one of which was related to the female.[246] Males claim their territory with singing and display flights with wing clapping.[8] Singing normally starts at dusk on calm evenings and may continue through the night, clear windless moonlit nights are preferred. The song is usually delivered from a perch, most often at medium height in trees or from the upper half near the canopy, sometimes in flight.[8][9] Males are responsive to playback during the period leading up to the breeding season (especially during courtship), to such a degree 45% territories would've been undetected in Spain if males has not responded to recordings (as opposed to listening for spontaneous callings).[247] Often between 8 and 50 pairs are recorded in different parts of the range in a typical range of 100 km2 (39 sq mi). In Scotland, about 17% of the 9-18 pairs per 10 km2 (3.9 sq mi) were non-breeders.[12] Typical territories for pairs are 50 to 100 ha (0.19 to 0.39 sq mi) in Finland when voles are plentiful. Several pairs may nest rather close together nonetheless. The minimal distance is normally around 50 to 150 m (160 to 490 ft) between active nests, but in Idaho a nearest nest distance of only 16 m (52 ft) was recorded.[8][13][36] When food is abundant, about 10-12 pairs, infrequently as many as 50, may nest within area of 100 km2 (39 sq mi). Pairs may tolerate each other in the same patch of trees while nesting if food supplies are abundant.[8][36] A study in Province of Pisa of Italy of 32 territories found 10-15 pairs per 100 km2 (39 sq mi) with a mean nest spacing of 1,727 m (5,666 ft).[233] In a south-central Idaho study area, pair occurred on average 0.65 km (0.40 mi) apart.[248] The highest densities may come from central Europe. The average density in central Europe is typically around 10-12 pairs per 100 km2 (39 sq mi).[48] However, in Brandenburg, Germany, over a 24-year study, it was found the average density was 72.7 pairs per 100 km2 (39 sq mi).[249] Based on studies from Michigan and Wyoming, anywhere from 10 to 100 pairs per 100 km2 (39 sq mi) was estimated, with the average range in Wyoming riparian habitat about 55 ha (0.21 sq mi).[9][13][82] Densities appeared lower in the Snake River area (0.28-0.42 pairs per square km) than elsewhere in southern Idaho (0.64-1.55 pairs per square km).[9][13] Globally, many pairs of long-eared owl occupy the same territory all year around but most prefer to use a different nest each year even if the same nest as last year is still in good standing. Females typically take on the duty of inspecting potential nesting sites and duets with its mate; perched on a chosen nest, she sings to contact the male, later vocal activity is confined to weak calls only heard at short range.[8][13] During displays, females have also been recorded doing the wing clap display but much less intensely than males.[48] Copulation tends to occur close to the nest. In Germany, it was recorded that the male precedes copulation with calls and display flights, followed by strong waving wing signals and tilting their body while perched near female and/or the nest.[37] Copulation has also been observed on both the ground and the trees, preceded frequently by a duet, a male aerial display which ending in descent to ground and a flight by the female.[13][37] Boundary fights between males are unrecorded in this species.[9] Breeding occurs later in the year than sympatric species such as tawny owls and barn owls perhaps due to their more strongly migratory ways. Rarely mating may occur early as February in cooler temperate areas, but the pairs copulations usually take place in March or April.[4] Winter breeding detected as new juveniles of 14–18 days of age were recorded in early February in Slovakia. Other prior reports of winter breeding are known from Italy, in two cases, as well as in the Czech Republic.[250][251]
Normally nests in stick nest of large birds, i.e.
Egg-laying is between normally between late March and early May in most of the range. Egg laying dates in the northeastern United States, in a sample of 42 eggs, were between March 14 and May 30. Additional records in southern Canada show laying as occurring at as late as June 5.[9][85] 43 eggs in Ontario were laid between March 19 to May 24, more than half between April 15 and May 5.[83] In northern Italy, the mean egg laying date was March 27.[233] Exceptional eggs were recorded as early as December 31 to January 3 in Spain.[262] Re-nesting can occur within about 20 days after a clutch is lost.[85] In Europe up to two broods have been successfully been raised at times of food abundance.[9][37] Generally the female lays 3-5 eggs (sometimes more if food is unusually abundant). Larger clutches are typical further north in the range.[8][9] Record sized clutches have been recorded for Europe of up to 8 eggs in Sweden in years of a “vole plague” while record sized clutches worldwide were recorded of 10–11 in the Kazan area of Russia in similar conditions.[4][36][68] In Great Britain, the average clutch size was recorded as 3.9 while in Germany it was 5.5 and, similarly, in Slovenia it was 5.6.[14][263][264] In a study from Montana, the mean clutch size was 5.[265] The pure white eggs are 40.2 mm × 32.5 mm (1.58 in × 1.28 in) on average in both North America and central Europe and weight about 23 g (0.81 oz).[8][85][266] At 1-5 day intervals (on average 2), the eggs are laid on the bottom of nesting area. A clutch of 7 eggs takes 10 to 11 days to lay.[8][9] Incubation begins with the first egg and continues for about 27–28 days (in extreme cases from about 21 to 30 days).[8][9][174] The female alone incubates while the male provides food, which is brought direct to nest. She may leave the nest early on to feed but does so much less later into incubation.[8][9] A study in Montana found that corticosterone levels were considerably higher in adults of both sexes during the breeding season than during the non-breeding season, suggesting that the breeding season is more stressful on the owls.[267]
The young hatch at 2 day intervals at any point between very late April and June.
Normally in North America the species produces one clutch per year, but 2 clutches in a year have been recorded in high vole years.[8] An exceptional double brood was recorded in Idaho due to high food availability, allowing the pair to successfully raise all 11 nestlings to fledgling, while in same season 3 other females in same grove were able to produce an average of 5.3 fledglings in their single broods.[269] Like other species using open nests, rather than enclosed cavities, the species has relatively short fledging period and quickly moves away from the dangerous situation of the nest site.[36] Nesting success averaged 46% between two study years in a study of 112 nests in Idaho with raccoon predation considered the most serious cause of nesting failure.[13] A different Idaho study of 24 nests showed that the owls fledged an average of 3.7 young per nest.[248] In Montana, the mean number hatched per nest was 3.8 and mean number to have fledged per nest was approximately 2.2.[265] 59% of 78 nesting attempts failed in Britain, with an average clutch size per successful pair of 3.91 to 4.53. 41 of 78 continuously monitored in this British study nest successfully produced 1 or more fledglings.[14] In another British study, of 58 monitored pairs over 4 years, 83% laid eggs, 63% hatched one or more young, and 57% fledged young, with an average of 3.2 young fledged per successful nest.[12] In yet another English study, this time exclusively of owls using wicker baskets, 50.7% of 71 attempts managed to fledge young. Among the wicker basket users, earlier nesters (i.e. March-early April) raised larger broods and had more fledglings than later (late April-early May), in part due to rising water tables making prey capture less ideal later in nesting season.[259] For 6 pairs of long-eared owls using wicker baskets in Israel, the mean brood size was 3.6 and mean number of young owls to leave the nest was 3.[260] At all stages and in all regions, reproduction tends to be more successful when prey populations are higher.[12][14] In continental Europe, conditions are better than in England or Finland, perhaps due to the large population of common voles there that are absent in the more northerly countries, and nesting success averages higher.[9][14][37] However, breeding success still is reliant on prey populations. In an 15 km2 (5.8 sq mi) area of southern Germany, one cold spring with few voles no breeding pairs were found. A year later, with a warm spring and many voles, 19 breeding pairs took up residence in the study area.[263] First year mortality of long-eared owls has been calculated in Germany as 52% and 31%.[73] In Brandenburg, Germany, of 867 breeding attempts, 36.6% (335) pairs were successful in raising 1,468 young, which equates to 1.57 fledgling per all pairs that attempted, 4.31 per successful pair. The Brandenburg data shows that after 1990, when conservation minded farming initiative began, numbers increased significantly. Also in Brandenburg, in one case, 2 successive females to the same male were killed, the male mate was able to pair with a third female and resulting in a late successful fledging (August 24).[249] In Slovenia, as studied between 1984 and 1993, of 79 nests, 32 (40%) produced young, 37 (47%) failed completely, and 10 (12%) failed after hatching. The Slovenian average number of owls hatched was 2.4 per nest (5.3 per successful nest) and the average number of owls fledged was 1.6 per nest (3.9 per successful nest).[264] In Pisa, Italy, long-eared owl pairs produced a mean of 0.95 per territorial pair and 2.13 per successful pair.[233] In central Slovenia, 57 nests produced an average of 5.7 eggs per clutch. Of the 51 fledged owls, 31 died in the study, 22 of which were due to mammal and bird predation, 6 due to starvation, 2 due to road collisions and 1 drowned in ditch.[264] In Britain, the most common diagnosed cause of nest failure was egg theft by humans (accounting for 28.2% of 46 failed nests).[14] Banding studies show that the long-eared owl typically have a short lifespan, with more than 91% of 105 owls recovered in North America of determined age being 4 years or younger. The oldest recorded in these efforts was banded in New York and recovered in Ontario at the age of 11 years and 4 months. Another one may have been over 15 years old, however.[100] One exceptional isolated record is known of a European long-eared owl of just under 28 years of age.[8][48] Annual survivorship in Germany and Switzerland for adults is 69%.[73]
Status
The long-eared owl is rather common and widespread in many regions. With a range of 80 million square kilometers, it is easily one of the most widely found owls. The
In
In art
John James Audubon illustrated the "Long-eared Owl - Strix otus" as Plate 383 in Birds of America, published London, 1827–38. The print was engraved by Robert Havell in 1837. The original watercolour was purchased from Audubon's destitute widow by The New York History Society.
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External links
- Long-eared Owl at owlpages.com, includes photos and call recordings
- Asio otus in Field Guide: Birds of the World on Flickr
- "Asio otus". Avibase.
- Feathers of Long-eared Owl (Asio otus) Archived 2013-12-03 at the Wayback Machine
- "Northern Long-eared Owl media". Internet Bird Collection.
- Long-eared Owl photo gallery at VIREO (Drexel University)