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Pseudoscops clamator

Striped Owl

  • Order: Strigiformes
  • Family: Strigidae
  • Polytypic 4 Subspecies

Authors: Thurber, Walter A., Rebecca Lohnes, and Thomas S. Schulenberg

Identification

Summary

The Striped Owl has a very distinctive appearance. A relatively large owl with prominent "ears" or "horns" (tufts of elongated feathers on the crown), Striped Owl takes its name from the heavy black streaking on buff-colored breast and belly. Another notable feature of Striped Owl is the very white color of the facial disks, which are boldly bordered with black.

The sexes are alike in appearance. No color morphs have been described in Striped Owl.

Similar Species

Striped Owl usually is separated readily from similarly-sized species. The Short-eared Owl (Asio flammeus) is another brown, streaked owl of open habitats (especially grasslands), but usually is found at higher elevations than Striped Owl. Short-eared Owl also has very short "ear" tufts, the iris color is yellow (not brown), the facial disks are brown (not white), and the plumage generally is darker brown. Stygian Owl (Asio stygius) has relatively long "ear" tufts, but is very dark in color overall, with dark facial disks and yellow irides.

Vocalizations

Like many owls, Striped Owls have a broad repertoire of sounds. Most sounds are vocal, but a few are mechanical and can be given singly or interspersed with vocal sounds. The significance of many vocalizations is not well known; indeed, many authors describe several different vocalizations for Striped Owl, but do not attempt to distinguish between "song" and "call." The vocalizations of adults generally fall into two categories, "hoots" and "barks" (see below). König and Weick (2008) equate the song with a series of hoots, whereas Lane (in Schulenberg et al. 2007) interpret a series of barks as the song; note also that there may be geographic variation in vocalizations within the Striped Owl (D. Lane, pers. comm.).

The Monosyllabic “Whoo”

One of the most characteristic sounds is a deep-toned “whoo." This call is often described as a “hoot,” but this is misleading because this incorrectly implies an abrupt beginning and termination of the call. A more satisfactory description is as "whoo," which softens the introductory consonant and drops the final consonant. This call sounds somewhat like the tone produced by blowing over a gallon jug.

The "whoo" of the female is of higher pitch than that of the male (Krahe 1981, Stiles and Skutch 1989).

There is the possibility that the "whoo" call is lacking in the repertoire of some populations of Striped Owl. It is documented to occur in Central America, and in northwestern and northern South America (e.g. this recording from Venezuela); but there are no known recordings of the "whoo" call from South America east of the Andes (D. Lane, pers. comm.).

Often, Striped Owls give two "whoo’s" in succession, “whoo -- whoo.” Doubling is commonplace, and the first note often goes unnoticed because it is unexpected. Usually the two segments are of equal intensity and are separated by an interval of 0.5-1.0 sec.: "WHOO -- WHOO." There are two variations: the first note might be soft, followed quickly by the second, giving the effect of a grace note: "whoo - WHOO"; or the first note might be louder than the second and more protracted: "WHOO – whoo" (Thurber and Komar 2006).

Striped Owls also occasionally deliver a “whisper song” with the bill closed. This song is soft and has a ventriloquist effect. The general form of this vocalization seems similar to normal hooting except that some low frequency sounds were suppressed (Thurber and Komar 2006).

Another vocalization that is given by Striped Owls is a bark. Barks can be given in succession at a slower rate than the rapid “whoo” call (de Oliveira 1980). They may also be given when surprised or threatened (Krahe 1981).

Multisyllabic Vocalizations

Striped Owls also give a “rattling call” consisting of a series of closely-spaced, short "barking" notes that increase in volume; the tempo may accelerate (Krahe 1981, Thurber and Komar 2006) or declerate (Lane in Schulenberg et al. 2007). This vocalization most often is performed by the male, but the female may join in and calling in unison or in chorus can be heard (Krahe 1981, Stiles and Skutch 1989, ffrench 1991).

Development of vocal repertoire

Owlets in the nest give a loud, high-pitched note varying little in pitch, but often varying in loudness, thus giving the impression of changes in pitch. These “squeal” or “scream” calls are probably contact calls, but also may be begging calls. Begging intensity increases close to sundown when the owlets presumably are the most hungry, and diminishes before midnight after they are fed.

Nonvocal Sounds

Striped Owls have several non-vocal sounds in their repertoire that are not often recorded because they occur at unexpected times. One sound is a snake-like hiss that typically is given by an owl exhaling forcefully with its bill wide open. One can stimulate this type of non-vocal sound in a hand-held owl by blowing in its face (Thurber and Komar 2006). This hiss might be a response to presumed danger.

A Striped Owl will snap its bill when agitated. Another sound produced by the bill is a rapid clattering not unlike drawing a card along a fine-toothed comb (Thurber and Komar 2006).

Sometimes, when a Striped Owl launches itself into flight from a high branch, the first thrust of its wings produces an audible flap. Although this sounds like a slap of the wings against the body, there is no physical contact between the two (Thurber and Komar 2006). The sound is more like the snap of a whip, similar in production to the individual wing beats of a drumming Ruffed Grouse (Bonasa umbellus).

Mechanical and vocal sounds may be intermixed. de Oliveira (1980) described an instance: a sequence begins always with a murmur which, within a few moments, increases in volume. Snaps of the bill are added, and then wing slaps; the excitement grows with continuous cracks that are similar to the discharge of a firearm.

Detailed Description (appearance)

Adult

Upperparts primarily are buffy brown, streaked with blackish and (especially on the black) vermiculated with white and gray. The outer webs of the scapulars are white or mostly white, forming a row of spots. An elongated (ca 3.5-5 cm) tuft of feathers over each eye is mostly blackish brown, with the buff or whitish buff outer margins. The facial disk, the lores, and a stripe over each orbit are white or whitish, with a distinct blackish border. The remiges have broad, dusky brown transverse bars; the base color of the remiges is buffy brown basally, and more distally the remiges vermiculated buffy and dusky. The rectrices also are barred with dusky brown; the base color of the outer rectrices primarily is cinnamon buff, but the inner rectrices are heavily vermiculated with gray, brown, and buff (thus, providing much less contrast with the dark transverse bars). The underparts are buffy brown, cinnamon buff or whitish buff, prominently streaked with dusky brown. The tarsi and toes are feathered, and are whitish buff or buff in color.

Nestlings

The hatchling Striped Owl is almost completely cloaked in down; the only bare patches are the eyeballs, the bill, and the sides and bottoms of the toes. The short-lived, first natal down (neoptile) is white or light gray. These feathers are fragile and quickly fragment or disintegrate; these feathers are replaced after a few days by the second natal down (mesoptile), which is tinged a pale Buff (Color 24, Smithe 1975). The resulting overall color of a Striped Owl nestling is thus a pale buff.

Juvenile

The subsequent plumages of Striped Owl have not been described in detail. Recently-fledged Striped Owls are generally buff in color, barred with gray or dusky, and the facial disk is mostly cinnamon, with a white border.

Bare Parts

Iris brown. Bill gray.

Measurements

Length


Female 40-57 cm


Male    33-38 cm

Mass


Female 400-570 g


Male     320-490 g

The wing measurements for a male and a female Striped Owl are respectively: wing chord 243 mm and 273 mm; maximum wing breadth 41 mm and 45 mm (Thurber and Komar 2006). With total body mass measurements of 342 g and 440 g, the aspect ratios of this male and female are about 6:1 to 8:1, respectively.

Molts

Molts of Striped Owl have not been studied in detail. In El Salvador, the latest date for down-cloaked owlets was 4 May, before the rains had started, at which time the owlets showed no signs of molt (Thurber and Komar 2006). Assuming an annual molt, it is likely that their first complete molt occurs between mid-May and November (the beginning of the next nesting season). The time necessary to complete the molt is unknown. In a captive population, two and a half month old birds were still in juvenile plumage (Krahe 1981).

In nestling Striped Owls, flight feathers develop early. Thurber (1978) shows a nestling, age about 40 days, still densely cloaked with buff down, and with remiges with rachi erupted about one-third of their length, one-third of their length still in sheathes, and the remainder concealed by the coverts. This bird was not yet able to fly.

Geographic Variation

Four subspecies of Striped Owl currently are recognized: forbesi, clamator, midas, and  oberi. Two of the subspecies have distributions that apparently are alloptatric to other subspecies, forbesi (Central America) and oberi (Tobago). The nominate subspecies, clamator, is found throughout most of the northern and central South America. It is replaced in the southern portions of the range of Striped Owl by midas, in southernmost Brazil, Uruguay, and Argentina. Differences between the subspecies are relatively minor, and primarily are differences in size and in plumage saturation. On the basis of current literature, the distributions of clamator and midas relative to one another are not well-defined.

The northernmost subspecies, forbesi, is relatively small. Subspecies oberi, endemic to the island of Tobabo, is darker than nominate clamator, with broader dark bars on the outer primaries. The southernmost subspecies, midas is reported to be larger and paler in color.

The aviary birds referred to by Krahe (1981) and Spicknall and Pickett (1983) probably were midas from Argentina.

Systematics

The Striped Owl has a superficial resemblance to several similarly-sized owls in the genus Asio, indeed it often has been placed in Asio or in the monotypic genus Rhinoptynx. The classification of Striped Owl in the genus Pseudoscops is based on differences in cranial osteology between clamator and several species of Asio (Olson 1995), although these differences were not considered in a phylogenetic context. More recently, Wink et al. (2008) presented a phylogenetic survey of the Strigiformes, using a Maximum Likelihood approach based on DNA sequence data from mitochondrial cytochrome b and from the nuclear RAG-1 and LDHb intron. In this study, the Striped owl consistently was nested within the genus Asio. Unfortunately, DNA samples were not available for the sole other species of Pseudoscops, the Jamaican Owl (Pseudoscops grammicus). Nonetheless, Wink et al. (2008) provide strong evidence that the many recent authors who consider the Striped Owl to be member of Asio indeed are correct (e.g. Marks et al. 1999, König and Weick 2008).

Recommended Citation

Thurber, Walter A., Rebecca Lohnes, and Thomas S. Schulenberg. 2009. Striped Owl (Pseudoscops clamator), Neotropical Birds Online (T. S. Schulenberg, Editor). Ithaca: Cornell Lab of Ornithology; retrieved from Neotropical Birds Online: http://neotropical.birds.cornell.edu/portal/species/overview?p_p_spp=36400