Species of owl
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The eastern screech owl (Megascops asio) or eastern screech-owl, is a small owl that is relatively common in Eastern North America, from Mexico to Canada. This species resides in most types of woodland habitats across its range, and is relatively adaptable to urban and developed areas compared to other owls. Although it often lives in close proximity to humans, the eastern screech owl frequently avoids detection due to its strictly nocturnal habits.
Taxonomy.
The eastern screech owl was formally described in 1758 by the Swedish naturalist Carl Linnaeus in the tenth edition of his "Systema Naturae". He placed it with all the other owls in the genus "Strix" and coined the binomial name "Strix asio". Linnaeus based his account on the "little owl" that had been described and illustrated by the English naturalist Mark Catesby in his book "The Natural History of Carolina, Florida and the Bahama Islands". The specific epithet is the Latin word for a type of eared owl. The eastern screech owl is now one of 22 screech owls placed in the genus "Megascops" that was introduced in 1848 by the German naturalist Johann Kaup. 
Five subspecies are typically recognised for the eastern screech owl, but the taxonomy in the species is considered "muddled". Much of the variation may be considered clinal, as predictably, the size tends to decrease from north to south and much of the color variation is explainable by adaptation to habitat.
Description.
Adults range from in length and weigh . Among the differently sized races, length can average from . The wingspan can range from . In Ohio, male owls average and females while in central Texas, they average and , respectively. They have either rusty or dark gray intricately patterned plumage with streaking on the underparts. Midsized by screech-owl standards, these birds are stocky, short-tailed (tail averages from in length) and broad-winged (wing chord averages from in length) as is typical of the genus. They have a large, round head with prominent ear tufts, yellow eyes, and a yellowish beak, which measures on average in length. The feet are relatively large and powerful compared to more southern screech owls and are typically feathered down to the toes, although the southernmost populations only have remnant bristles rather than full feathering on the legs and feet. The eastern screech owl (and its western counterpart) are actually some of the heaviest screech owls; the largest tropical screech owls do not exceed them in average or maximal weight, but (due to the eastern screech owls' relatively short tails) they are surpassed in length by Balsas ("M. seductus"), long-tufted ("M. sanctaecatarinae"), white-throated ("M. albogularis"), and rufescent owls ("M. seductus"), in roughly increasing order.
Two color variations are referred to as "red or rufous morphs" and "gray morphs" by bird watchers and ornithologists. Rusty birds are more common in the southern parts of the range; pairings of the two color variants do occur. While the gray morph provides remarkably effective camouflage amongst the bark of hardwood trees, red morphs may find security in certain pine trees and the colorful leaves of changing deciduous trees. The highest percentage of red morphs is known from Tennessee (79% of population) and Illinois (78% of population). A rarer "brown morph" is known, recorded exclusively in the south (i.e. Florida), which may be the occasional product of hybridation between the morphs. In Florida, brown morphs are typically reported in the more humid portions of the state, whereas they appear to be generally absent in the northern and northwestern parts of the state. A paler gray variation (sometimes bordering on a washed-out, whitish look) also exists in western Canada and the north-central United States.
Confusion with other species.
In the closely related western screech owl ("Megascops kennicottii"), no color morphs are known; all owls of the western species are gray. Besides coloration, the western screech owl is of almost exactly the same general appearance and size as the eastern. The only reliable distinguishing feature is the bill color, which is considerably darker (often a black-gray) in the western and olive-yellow in the eastern; their voices also differ. The eastern and western screech owls overlap in the range in the Rio Grande valley at the Texas–Mexico border and the riparian woods of the Cimarron tributary of the Arkansas River on the edge of southern Great Plains. Other somewhat similar species that may abut the eastern screech owl's range in its western and southernmost distribution, like the Middle American screech owl ("Megascops guatemalae"; formerly called "vermiculated screech owl"), whiskered screech owl ("Megascops trichopsis"), and the flammulated owl ("Psiloscops flammeolus"), are distinguished by their increasingly smaller body and foot size, different streaking pattern on breast (bolder on the whiskered, weaker on the others), different bare part coloration, and distinctive voices. Through much of the eastern United States, eastern screech owls are essentially physically unmistakable, because other owls with ear tufts are much larger and differently colored and the only other small owl, the northern saw-whet owl ("Aegolius acadius") is even smaller, with no ear tufts, a more defined facial disc, and browner overall color.
Plumage polymorphism.
Eastern screech owls exhibit a similar polymorphism as tawny owls, whose plumage ranges from rufous to gray. The inheritance of morph in owls is likely complex, but rufous plumage may be controlled by a dominant allele and gray plumage alleles are recessive. There are latitudinal clines in screech owl polymorphism, with northern latitudes containing mostly gray individuals and southern latitudes containing primarily rufous individuals. This cline may be driven by higher metabolic rates in rufous individuals compared to gray individuals. Evidence of higher metabolic rates was shown by a higher proportion of gray morphs in the rural areas surrounding Waco, TX compared to the warmer suburban areas. Rufous screech owls also had higher mortality during cold winters.
Distribution and habitat.
Eastern screech owls inhabit open mixed woodlands, deciduous forests, parklands, wooded suburban areas, riparian woods along streams and wetlands (especially in drier areas), mature orchards, and woodlands near marshes, meadows, and fields. They try to avoid areas known to have regular activity of larger owls, especially great horned owls ("Bubo virginianus"). Their ability to live in heavily developed areas outranks even the great horned and certainly the barred owl ("Strix varia"); screech owls also are considerably more successful in the face of urbanization than barn owls ("Tyto alba") following the conversion of what was once farmland. Due to the introduction of open woodland and cultivated strips in the Great Plains, the range of eastern screech owls there has expanded. Eastern screech owls have been reported living and nesting in spots such as along the border of a busy highway and on the top of a street light in the middle of a busy town square. They often nest in trees in neighborhoods and urban yards inhabited by humans. In such urban environments, they often meet their dietary needs via introduced species that live close to humans such as house sparrows ("Passer domesticus") and house mice ("Mus musculus"). They also consume anole lizards and large insects such as cicadas. They occupy the greatest range of habitats of any owl east of the Rockies. Eastern screech owls roost mainly in natural cavities in large trees, including cavities open to the sky during dry weather. In suburban and rural areas, they may roost in manmade locations such as behind loose boards on buildings, in boxcars, or on water tanks. They also roost in dense foliage of trees, usually on a branch next to the trunk, or in dense, scrubby brush. The distribution of the species is largely concurrent with the distribution of eastern deciduous woodlands, probably discontinuing at the Rocky Mountains in the west and in northern Mexico in the south due to the occupation of similar niches by other screech owls and discontinuing at the start of true boreal forest because of the occupation of a similar niche by other small owls (especially boreal owls ("Aegolius funereus"). Eastern screech owls may be found from sea level up to in elevation in the eastern Rocky Mountains and up to in the eastern Sierra Madre Oriental Mountains, although their altitudinal limits in the Appalachian Mountains, near the heart of their distribution, is not currently known.
Behavior.
Eastern screech owls are strictly nocturnal, roosting during the day in cavities or next to tree trunks. They are quite common, and can often be found in residential areas. However, due to their small size and camouflage, they are much more frequently heard than actually seen. These owls are frequently heard calling at night, especially during their spring breeding season. Despite their name, this owl does not truly screech. The eastern screech owl's call is a tremolo with a descending, whinny-like quality, like that of a miniature horse. They also produce a monotone purring trill lasting 3–5 seconds. Their voices are unmistakable and follow a noticeably different phrasing than that of the western screech owl. The lugubrious nature of the eastern screech owl's call has warranted description such as, "A most solemn graveyard ditty, the mutual consolation of suicide lovers remembering the pangs and delights of the supernal love in the infernal groves, "Oh-o-o-o-o that I never had been bor-r-r-r-n!".
Breeding.
Their breeding habitat is deciduous or mixed woods in eastern North America. Usually solitary, they nest in a tree cavity, either natural or excavated by a woodpecker. Holes must have a entrance to accommodate this owl. Usually, they fit only in the holes excavated by northern flickers ("Colaptes auratus") or pileated woodpeckers ("Dryocopus pileatus"), as apparently the midsized red-bellied woodpecker ("Melanerpes carolinensis") make holes that are not large enough to accommodate them. Orchards, which often have trees with crevices and holes, as well as meadow voles ("Microtus pennsylvanicus"), a dietary favorite, are often preferred nesting habitats. Eastern screech owls also use nesting boxes erected by humans. Although some people put up nest boxes meant for screech owls, the owls also take over nest boxes meant for others, such as those for wood ducks ("Aix sponsa"), houses erected for purple martins ("Progne subis"), and dovecotes put up for rock doves ("Columba livia"), occasionally killing and consuming at least the latter two in the process of taking over the nest box. A 9-year study comparing the breeding success of eastern screech owls nesting in natural cavities and nesting in nest boxes showed that the fledging rate was essentially the same, although in some years, up to 10% more success occurred in the natural cavities. Depending on the origins of the hole being used, eastern screech owl nests have been recorded from off the ground. Like all owls, these birds do not actually build a nest; instead, females lay their eggs directly on the bare floor of the nest hole or on the layer of fur and feathers left over from previous meals that line the bottom of its den. Breeding pairs often return to the same nest year after year.
This species commences egg laying on average about two months after great horned owls, but about two weeks before American kestrels ("Falco sparveius") and almost throughout the range lays its first egg at some point in April. Eggs are laid at two-day intervals and incubation begins after laying of the first egg. Eggs vary in size in synch with their ultimate body size, ranging from an average of in the Northern Rockies to in south Texas. From one to six eggs have been recorded per clutch, with an average of 4.4 in Ohio, 3.0 in Florida, and 4.56 in the north-central United States. The incubation period is about 26 days, and the young reach the fledging stage at about 31 days old. Females do most of the incubating and brooding, but males also occasionally take shifts. As is the typical division of labor in owls, the male provides most of the food while the female primarily broods the young, and they stockpile food during the early stages of nesting, although the male tends to work hard nightly because many nestlings often appear to live almost entirely on freshly caught insects and invertebrates. The male's smaller size make it superior in its nimbleness, which allows it to catch insects and other swift prey. Eastern screech owls are single-brooded, but may renest if the first clutch is lost, especially towards the southern end of its range. When the young are