Barred owl
The barred owl, also known as the northern barred owl, striped owl or, more informally, hoot owl or eight-hooter owl, is a North American large species of owl. A member of the true owl family, Strigidae, they belong to the genus Strix, which is also the origin of the family's name under Linnaean taxonomy. Barred owls are largely native to eastern North America, but have expanded their range to the west coast of North America where they are considered invasive. Mature forests are their preferred habitat, but they can also acclimatise to various gradients of open woodlands. Their diet consists mainly of small mammals, but this species is an opportunistic predator and is known to prey upon other small vertebrates such as birds, reptiles, and amphibians, as well as a variety of invertebrates.
Barred owls are brown to gray overall, with dark striping on the underside. Barred owls have typical nesting habits for a true owl, tending to raise a relatively small brood often in a tree hollow or snag in forested areas. As a result of the barred owl's westward expansion, the species has begun to encroach on the range of the related and threatened spotted owl. Evidence shows the assorted threats posed by the invading barred species are only increasing. In response, biologists have recommended culling operations to mitigate the negative effect of the barred on the spotted owl species.
Basics
The barred owl was first described by Philadelphia naturalist Benjamin Smith Barton in 1799. The species was named due to the varied directions the dusky markings take on their underside.The barred owl is roughly intermediate in size between the larger Ural and the smaller tawny owl, but the structural features of its relatively short and decurved claws more so resemble the tawny species as does their dietary and habitat ecology. The spotted owl has been hypothesized to be within a superspecies with the barred owl. However, genetic testing reveals very early divergence between spotted and barred owls. A fossil species once called Strix brea from the early Pleistocene in California does little to resolve the ancestry of modern species, given its ambiguous relation to any living Strix. The fossil species was larger and longer-legged than either the spotted and barred owls, and is now considered to be in a separate genus, Oraristrix. Pleistocene era fossils of probable barred owls are known from Florida, Tennessee and Ontario.
Subspecies
The subspecies of the barred owl vary mostly by region, with slight to moderate variation by coloring, size and extent of feathering on the toes. Although several have been described in the past, the barred owl may include only three subspecies, subsequent to the separation of the fulvous and cinereous forms.- S. v. varia : The northern barred owl. This race lives throughout the Northeastern United States and the Upper Midwest, ranging as far south as Oklahoma, the Carolinas and northern Georgia. It is also considered to comprise all western "invader" birds found as far west as California and British Columbia. However, genetic study of westerly birds show a substantial isolation, possibly up to the subspecific level, of the western and eastern populations of the northern owls, with an estimated divergence of around 7,000 years, perhaps indicating an unknown history of the species in remote forests of northern and central Canada that radiated more recently to comprise the western populations. This race is generally the typical mid gray-brown variety of barred owl. However, a paler variation with very washed out markings and a more pure whitish base color is known, formerly considered a race S. v. albescens, as well as darker and browner variation in northern Minnesota. This race is fairly large. The wing chord and tail length may measure from and in males and and in females. One nominate bird had a tarsus length of and the culmen from the cere may measure.
- S. v. georgica : The southern barred owl or, alternately, the Florida barred owl. This subspecies is found in southern North Carolina closer to the coast along to broadly through Georgia and all of Florida. This is the smallest of the three subspecies on average. Known wing chord lengths can vary from. Tail length is and the bill from the cere is. Males in Florida were found to weigh from, with averages in two samples of, while two females weighed, respectively. It therefore appears to show less pronounced sexual dimorphism than the northern barred owl race.
- S. v. helveola : The Texas barred owl. Comprises most barred owls found in Texas. The distributional range is considered to range as far north as Lee County, east to Chambers County, west to Kerr County and south to Nueces County. In this race, the ground coloration tends to pale gingery-cream and the back and head tend to be a pale brown ranging into an almost cinnamon color. The toes can vary from rather bare to slightly bristled. This race is similar to other barred owls in size, perhaps averaging marginally smaller than those in the nominate race, but its bill and feet are larger on average than the preceding two races.
Description
The barred owl has well-developed eye anatomy. As is typical of owls, their ocular anatomy is quite distinct from diurnal raptors especially in terms of their photoreceptor cells, as they have a very large number of rod cells in their quite sensitive retina. However, their pecten oculi is smaller relative to the size of their large ocular globe. The vision in limited or almost no light during a laboratory study of a barred owl was found to be similar to that of other owls, including the long-eared owl and the American barn owl. The tarsi and toes are feathered up to the dark gray, black-tipped talons. These feathers are more sparse and bristled in the southern races. On individuals with bare sections of their toes, the toes are yellowish-gray in color. The flight feathers are barred with whitish buff and brown while the tail is brown or grayish-brown with 4–5 whitish bars. Young barred owls with their second set of down feathers are fluffy brownish-white, with indistinct darker barring on their head, back and mantle. They quickly become juveniles which resemble adults but have less distinct markings, more buff coloring overall, often some remnant down, pinkish skin and a pale, blue-green cere. Also the tail at this age may have as many as seven bands. Full adult plumage is obtained via molt after about a year as well as adult bare part characteristics. A study of tail molt in Washington showed that molt tends to occur relatively quickly, and that young individuals are difficult to age by state of molt alone. Southern barred owls tend to be darker and slightly smaller than northerly ones. Rare captive and wild barred owls with albinism have been described and are pure white but tend to retain their brown eyes.
The barred owl is a large species. The adult measures anywhere from in length while the wingspan may range from. The wing area is quite intermediate among American owls, with the wing loading being lower than larger, but proportionately small-winged larger owls and even than some smaller owls. The barred has high wing-loading. Wing-loading is related to hunting technique, with higher wing-loading owls typically hunting from a perch, with only a brief flight necessary to obtain food, whilst lower wing-loading owls often hunt their prey from active flight. As is the case in most owls, the various wing feathers of barred owls are uncharacteristically soft and bear a comb-like shape, which in turn renders their flight functionally silent during their hunts. Like most birds of prey, the female is larger than the male barred owl, sometimes described as reverse sexual dimorphism.
Among standard measurements, the wing chord of grown males varies from, with an average from three sources of, the tail may measure from, with an average of and the culmen from the cere may measure from, with an average of. Meanwhile, for the female, the wing chord may range from, averaging, the tail from, averaging and the culmen from the cere, averaging. Sexual dimorphism is particularly pronounced in barred owls by body mass as males within a population are sometimes a third lighter in weight. In the nominate subspecies, average weights for males have been reported as , and in three samples. The weight range for adult males is known to vary from. The considerably larger female of the nominate subspecies has been reported to average , and . Altogether, fully-grown female barred owls may weigh from.
Vocalization
The barred owl is a powerful vocalist, with an array of calls that are considered "spectacular, loud and emphatic". Calls probably carry well over. Its usual call is a series of eight accented hoots ok-ok-ok-ok ok-ok-buhooh, or the "typical two-phrase hoot" with a downward pitch at the end. The most common mnemonic device for remembering the call is "Who cooks for you, who cooks for you all." Due to its best known call, the barred owl is sometimes colloquially referred to as Old Eight-Hooter. At 80% of study posts in Virginia, barred owls responded to playback of this call. A further call is the "ascending type" or the "legato" call, a series of variable notes ending in oo-aw or hoo-aah. At least two other variations on the legato/ascending call are known. 56% of studied owls in Virginia engaged in the ascending type call but 36% uttered only the closing notes. The isolated hoo-aah, sometimes called the "inspection call", was the most common song type in north Florida and the most likely to be heard during daylight. Several other calls, although some are not dissimilar variations on the main calls, are known. Some of these vary into cackles, hoots, caws and gurgles, at times described as "sudden demonic laughter", "cat-like screams" and "prolonged outbursts of cackling" and seem to be, among Strix species, an idiosyncrasy endemic to the barred owl.Another call type is the "mumble", a grumbling, slurred and subtle err-ERR-err, also an up-and-down "twitter" call at a high pitch. When agitated, this species will make a buzzy, rasping hiss about three times in three seconds, repeating every 10–30 seconds, and will click its beak together forcefully. Females and juveniles beg with high scratching skreeechch notes. The voice of the two sexes is similar, but the female has a higher-pitched voice with longer terminal notes. Of calls, 87 to 94% are identifiable to sex per one study. While calls are most common at night, the birds do call during the day as well, especially when provoked by human playback or imitation. They are more responsive than any hawk in the east to playback of calls of their own species. The barred owl is noisy in most seasons but peak vocalization times for barred owls tend to be between late January and early April. Two seasonal peaks in vocalizations, one right before breeding and another after the young have dispersed, were detected in Connecticut, with peak vocalizations on nights with extensive cloud cover. Peak times for vocalizations are between 6:00pm and 6:00am, with the least frequent vocalizations around mid-afternoon.