Eastern screech owl

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.[4] 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.[10]

Five subspecies are typically treated 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.

• M. a. asio (Linnaeus, 1758) includes previously described races no longer considered valid such as M. a. carolinensis, M. a. naevius and M. a. striatus. It is resident from eastern Minnesota to southwestern Quebec and southern New Hampshire south to Missouri, Tennessee, and northern South Carolina. Dorsal color is cold gray; the red morph is common (about 39% of overall population).[11] The nominate's markings are coarse and sparse and its toes are densely feathered. Its primary song has a terminal, tremulous whinny. This is a medium-to-large race, measuring 14 to 18 cm (5+1⁄2 to 7 in) in wing chord length. The owls of southern Ontario are on the larger end of the scale, of similar size to the relatively big owls of Colorado and Wyoming.[12]
• M. a. maxwelliae (Ridgway, 1877). Includes M. a. swenki. Resident from central Montana, southeastern Saskatchewan, and southern Manitoba south to western Kansas. This race is similar to M. a. asio but dorsal color tends to be a paler gray, the ventrum being whiter and less heavily marked and red morphs tending to paler and rarer (~7% of population[11]). With a wing chord length of 15 to 18 cm (6 to 7 in), this is the largest race in average linear measurements.[13] This subspecies was named in honor of Martha Maxwell by ornithologist Robert Ridgway of the Smithsonian Institution.[14]
• M. a. hasbroucki (Ridgway, 1914). Replacement name for the formerly described M. a. trichopsis. This subspecies is a resident from Oklahoma panhandle and southern Kansas south to Edwards Plateau of central Texas. This subspecies is also similar to M. a. asio but the dorsal color is buffy gray, the red morph being rare (~5% of population), and markings coarse and dense. This race averages at a similar size as the first two, at 14 to 18 cm (5+1⁄2 to 7 in) in wing chord length.
• M. a. mccallii (Cassin, 1854) includes previously described races such as M. a. enano and M. a. semplei. Resident from southern Texas (Big Bend to lower Rio Grande Valley) and northwestern Chihuahua and northern Coahuila southeast to eastern San Luis Potosí, this race is similar to M. a. hasbroucki, but its markings are fine and dense so the dorsum looks heavily mottled, with red morphs being rare (apparently entirely absent in South Texas). Its body size is smaller to the northern races, with a wing chord length of 13 to 17 cm (5 to 6+1⁄2 in). Unlike other subspecies, the primary song of M. a. mccallii lacks a terminal whinny.
• M. a. floridanus (Ridgway, 1873) is resident in Florida and southern Georgia west through Gulf Coast states to western Louisiana and north in the Mississippi River valley to southeastern Arkansas. This race's dorsal color is often rusty-brown (red morph equally common), with fine and dense markings. As described above, this subspecies may occur in a true "brown morph". It is the smallest race of eastern screech owl, ranging in wing chord length from 13 to 16 cm (5 to 6+1⁄2 in).

Eastern screech owls exhibit a similar polymorphism as tawny owls, where 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.[15] Evidence of higher metabolic rates was show by a higher proportion of gray morphs in the rural areas surrounding Waco, TX compared to the warmer suburban areas.[16] Rufous screech owls also had higher mortality during cold winters.[15]

Juvenile eastern screech owl

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 7 to 20 cm (3 to 8 in) 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.[18] Orchards, which often have trees with crevices and holes, as well as meadow voles (Microtus pennsylvanicus), a dietary favorite, are often preferred nesting habitats.[4] 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 pigeons (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.[18] Depending on the origins of the hole being used, eastern screech owl nests have been recorded from 1.5 to 25 m (5 to 80 ft) off the ground.[4] 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.[19]

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.[4] 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 36.3 mm × 30.2 mm (1+7⁄16 in × 1+3⁄16 in) in the Northern Rockies to 33.9 mm × 29.2 mm (1+5⁄16 in × 1+1⁄8 in) in south Texas.[4] 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.[20] 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.[4][8] 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 small, the female tears the food apart for them. The female, with her larger size and harder strike, takes on the duty of defending the nest from potential threats, and even humans may be aggressively attacked, sometimes resulting in them drawing blood from the head and shoulders of human passers-by.[4]

Fuertes portrait of a red and gray morph eastern screech owl

Like most predators, eastern screech owls are opportunistic hunters. Due to the ferocity and versatility of their hunting style, early authors nicknamed eastern screech owls "feathered wildcats".[21] In terms of ecological niche, they have no easy ecological equivalent in Europe, perhaps the closest being the little owl (Athene noctua), the similar looking Eurasian scops owl (Otus scops) being smaller and weaker and the long-eared owl (Asio otus) more fully dependent on rodents. The success of eastern screech (and western screech) owls in North America may be the reason long-eared owls are much more restricted to limited northern forest habitat in North America than they are in Europe.[4] Eastern screech owls hunt from dusk to dawn, with most hunting being done during the first four hours of darkness. A combination of sharp hearing and vision is used for prey location. These owls hunt mainly from perches, dropping down onto prey. Occasionally, they also hunt by scanning through the treetops in brief flights or hover to catch prey. This owl mainly hunts in open woodlands, along the edges of open fields or wetlands, or makes short forays into open fields. When prey is spotted, the owl dives quickly and seizes it in its talons. Small prey usually is swallowed whole on the spot, while larger prey is carried in the bill to a perch and then torn into pieces. An eastern screech owl tends to frequent areas in its home range where it hunted successfully on previous nights. The eastern screech owl's sense of hearing is so acute, it can even locate mammals under heavy vegetation or snow. The bird's ears (as opposed to its ear tufts) are placed asymmetrically on its head, enabling it to use the differences between each ear's perception of sound to home in on prey. Additionally, the feathers the eastern screech owl uses to fly are serrated at their tips. This muffles the noise the bird makes when it flaps its wings, enabling it to sneak up on prey quietly. Both the specialized ear placement and wing feathers are a feature shared by most living owl species to aid them in hunting in darkness.[19]

During the breeding season, large insects are favored in their diet, with invertebrates often composing more than half of the owls' diet. Some regularly eaten insects include beetles, moths, crickets, grasshoppers, katydids,[22] and cicadas, although they likely consume any commonly available flying insect. Also taken are crayfish, snails, spiders, earthworms, scorpions, leeches, millipedes, and centipedes. Small mammals, ranging in size from shrews to young rabbits (Sylvilagus ssp.), are regular prey and almost always become the owl's primary food during winter. Small rodents such as microtine rodents and mice account for about 67% of mammals taken, although rodents of a similar weight to the owl, such as rats and squirrels, especially the red squirrel (Tamiasciurus hudsonicus), are also taken. Jumping mice (Zapus ssp.), chipmunks, moles, and bats (especially the little brown bat (Myotis lucifugus) may be taken occasionally. Small birds such as chickadees (Poecile ssp.), swallows, sparrows, finches, flycatchers,[23] and warblers are the most common avian prey, and such species are normally caught directly from their nocturnal perches or during nocturnal migration. In Ohio, the most commonly reported avian prey species, and most commonly stored food items behind meadow voles, were yellow-rumped warblers (Setophaga coronata) and white-throated sparrows (Zonotrichus albicollis).[20] Abundant midsized avian or largish passerine prey are also not uncommon foods, such as mourning doves (Zenaida macroura), downy woodpeckers (Picoides pubescens), northern flickers, blue jays (Cyanocitta cristata), American robins (Turdus migratorius), European starling (Sturnus vulgaris), red-winged blackbirds (Agelaius phoeniceus), and common grackles (Quiscalus quiscula). However, larger avian prey are sometimes caught, including northern bobwhite (Colinus virginianus) and American woodcocks (Scolopax minor) and even rock pigeons and ruffed grouse (Bonasa umbellus), most likely young or fledgling aged birds, but all of which are likely to be heavier than the screech owls themselves. All told, more than 100 species of bird have been hunted by eastern screech owls. Irregularly, small fish, small snakes (i.e. Heterodon ssp.), lizards, baby soft-shelled turtles (Apalone ssp.), small frogs such as tree frogs and northern leopard frogs (Lithobates pipiens), toads, newts, and salamanders are also preyed upon. They have even been observed hunting for fish at fishing holes made by people or cracks in ice at bodies of water during winter. The most commonly reported fish prey in Ohio were American gizzard shad (Dorosoma cepedianum) and green sunfish (Lepomis cyanellus).[20][24] Brown bullheads (Ameiurus nebulosus) have been captured by eastern screech owls along coastal areas during winter.[4]

From hundreds of prey remains from Ohio, 41% were found to be mammals (23% of which were mice or voles), 18% were birds, and 41% were insects and other assorted invertebrates. Of vertebrates taken in the nesting season, 65% were birds (of about 54 species), 30% were mammals (11% meadow voles; 8% each of house mice and deermice of the genus Peromyscus), 3% were fish, and less than 2% were reptiles and amphibians.[20] In Michigan, among winter foods, 45–50% were meadow voles, 45% were white-footed mice (Peromyscus leucopus) and 1–10% were birds; during the summer, these respective numbers changed to 30, 23, and 19%, with as much as 28% of the food in summer being crayfish (Cambarus ssp.).[25] Due to meeting the needs of their nestlings, eastern screech owls frequently consume less per day during summer than they do during winter. Five owls captured in April, averaging about 160 g (5+3⁄4 oz) in males and 190 g (6+3⁄4 oz) in females, gained on average 28 g (1 oz) when captured in fall (October–December) and 13 g (1⁄2 oz) when captured in winter (January–February).[20] In Michigan, screech owls consumed about 25% of their own weight per day during winter against 16% of their weight in summer. The average weight of vertebrate prey for screech owls in Michigan is 26 g (15⁄16 oz)[25] In Wisconsin, the average weight of vertebrate prey is 28 g (1 oz).[26] While much of their insect prey can weigh only a fraction of a gram, their largest prey, such as adult rats and pigeons and juvenile rabbits and gamebirds, can weigh up to at least 350 g (12+1⁄4 oz).[4]

Eastern screech owls are known for their ability to live in close proximity to humans. There is previous information pointing to potential behavioral adaptations of urban and suburban eastern screech owls from their rural counterparts. There have been previous studies that found suburban eastern screech owls breed no differently in man-made nest boxes than in natural tree cavities.[27] Climate, food sources, and predator presence are some potential factors that impact the behaviors of suburban and rural eastern screech owls.[28] Living in suburbia can have some additional impacts on eastern screech owl behavior such as secondary poisoning, vehicles, and more predation and competition from raccoon, opossum and squirrels.[28]

Previous research has shown that male eastern screech owls find and defend two to three potential nesting sites (man-made and natural) in order to have backups for failed first nesting attempts. However, in a study by Gehlbach[27] it was found that suburban eastern screech owls had fewer alternative nesting sites due to humans cutting down trees with natural cavities, pruning the trees, or filling in the natural cavities with cement. Gehlbach[27] also found that nesting sites close to houses and with fewer surrounding shrubs were some of the most used. Additionally, older eastern screech owls were found to be more likely to habituate to human disturbances compared to younger eastern screech owls. A study by Artuso[29] found that there were larger average brood sizes and earlier average fledging dates of eastern screech owls shown in moderate and high-density suburban areas than in low-density suburban and rural areas.[29] Urban and suburban populations of eastern screech owls are more dense and productive than their rural counterparts.[30] There are various differences in habitat that have impacts on the nesting behaviors of eastern screech owls.

Eastern screech owl feeding behaviors have also been shown through previous research to be impacted by whether the owl lived in a rural or suburban area. In a previous study, prey diversity for eastern screech owls peaked in low-density suburban areas.[29] The owl's feeding habits changed based on the habitat type—owls in low-density suburban sites consumed almost double the amount of birds in non-breeding season as owls in high-density sites and triple that of owls in rural sites. Rural owls generally consumed more invertebrates and fewer caterpillars and earthworms.[29] It is already known that eastern screech owl diets vary throughout the breeding and non-breeding season, but now there is more research describing habitat's role in feeding behaviors as well.

The climate within urban or suburban and rural areas differ as well which in turn impacts eastern screech owl behavior. Suburban climate is typically warmer than rural climate due to the "heat island effect".[31] A previous study showed that as suburban climates got warmer over the course of a few years, eastern screech owls started nesting an average of 4.5 days earlier annually.[30] There were also more avian prey and a 93% success rate in annual nests. Bird baths and feeders located in the suburban habitats were also noted as being likely factors in enhancing residence successes.[30]  

This species has the potential to be infected by several parasites, including Plasmodium elongatum, Plasmodium forresteri, and Plasmodium gundersi.