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Morphs of the Eastern Screech-Owl by Ron Pittaway

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Morphs of the Eastern Screech-Owl by Ron Pittaway @~u&[MD@ wD[M[Q)~i I The Journal of the Ontario Field Ornithologists Volume 13 Number 2 August 1995 66 Recognizable Forms Morphs of the Eastern Screech-Owl by Ron Pittaway Introduction Taxonomy The Eastern Screech-Owl (Otus asiol Godfrey (19861 and James (19911 list is a widespread resident in southern O.a. naevius as the only subspecies Ontario south of the Canadian Shield [race] of the Eastern Screech-Owl in (James 19911. It prefers small Ontario. A much paler subspecies deciduous or mixed woodlots with swenki breeds in western Manitoba, mature trees and snags for roosting intergrading with eastern naevius at and nesting. The Eastern Screech -Owl Winnipeg and Whitemouth. These is strictly nocturnal. During the day it locations are shown on the map on usually perches close to the trunk of the inside cover of The Birds of a thick evergreen or roosts in a Canada (Godfrey 19861. Other natural cavity or old flicker hole, subspecies in North America are rarely more than 10 metres up. On listed in the American Ornithologists' winter days it often sits in the Union Check-list (19571. This entrance of a south-facing hole, treatment of subspecies is in need of absorbing the warm sunlight. If revision. I agree with DeBenedictis disturbed, it retreats down the hole. (19771 that the most sensible Many birders are familiar with its treatment of subspecies is by two common calls: a short horse-like Marshall (19671 who lists five whinny in the fall and winter, and a subspecies: nominate O.a. asio toad-like trilling in the spring and (includes naevius of the AOU 1957 nesting season. and Godfrey 19861 of the East, O,a. Field guides illustrate and maxwelliae (includes swenki of the describe two colour morphs [phases], AOU 1957 and Godfrey 19861 of the gray and red, of the Eastern Screech- Great Plains, O.a. floridanus of Florida Owl. Both the gray and red morphs west to Mississippi, o.a. hasbrouchi of are illustrated in the Peterson's Guide Texas, and O.a. mccallii of the Rio (19801. the Golden Guide (Robbins et Grande Valley. al. 19831 and the National Geographic Morphs vary in hue depending on Guide (Scott 19871. In addition, there whether the subspecies is dark or is a little-known brown or pale. For example, compare the intermediate morph. In this account eastern gray morph with the paler I discuss the identification, western gray morph maxwelliae frequency, genetics, and some (includes swenkij on page 243 of the ecological differences of the three National Geographic Guide (Scott morphs of the Eastern Screech-Owl 19871. Similarly, the red morph of the in Ontario. The three morphs are western maxwelliae is paler than the illustrated in Voous (19881 and by eastern red morph. Peter Burke in Figure 1. ONTARIO BIRDS AUGUST 1995 67 Figure 1: Gray Morph (top). Brown Morph (middle). and Red Morph (bottom). Note differences in feather markings. Drawing by Peter Burke. VOLUME 13 NUMBER 2 68 Why are the three morphs of the Morph Genetics Eastern Screech-Owl not considered The three morphs vary in colour and subspecies? Subspecie~ are forms in the extent and pattern of the dark having separate breeding ranges, markings on their feathers. See Figure interbreeding where their ranges 1. Out of a total of 1320 specimens meet. Morphs are forms occurring in examined by Owen (1963) from the same breeding range, with throughout the range, 54 percent different morphs even occurring in were gray, 38 percent red and 8 the same brood. The third part of the percent intermediate (brown). In his scientific name is the name of the study, Owen divided 833 screech- subspecies, for example, Otus asio owls from selected areas into six naevius is the subspecies in Ontario colour types, grading from gray to (A.O.D. 1957). It has three morphs. red: two gray, two intermediate Morphs do not have scientific names. (brown), and two red. Figure 2 shows In screech-owls, the morphs are more the strong bimodal (gray and red) recognizable than the subspecies! distribution of the morphs and the continuous variation between the Plumages, Molts, Aging morphs. and Sexing The gray, brown and red morphs The sexes are similar in all ages and are not linked to age, sex or plumages. Juveniles [juvenals] in subspecies. A bird is born a certain. summer are narrowly barred all over, morph and remains that colour all 1tS except on the wings and tail which life. All three morphs have been are much like the adult. Gray and red observed in the same brood [Hrubant morph juveniles usually are 1955, Smith 1993). There are two distinguishable in the field. See the main theories for the three morphs: illustration of the gray morph (1) the gray and red morphs are due juvenile on page 243 in the National to one gene having two alleles Geographic Guide (Scott 1987). In (forms) with red dominant over gray, late summer and early fall, juveniles with the brown morph due to other undergo a partial molt to first year modifying genes; (2) the morphs are (first basic) plumage, retaining the due to one gene having three alleles juvenile wings, scapulars and tail. with a graded order of dominance, First year birds and adults (definitive red over brown over gray (Hrubant basic) are similar in appearance. First 1955, Owen 1967, VanCamp and year birds (when they are one year Henny 1975, DeBenedictis 1977). old) and adults undergo a complete There is no clear resolution of which molt from late July to mid-November hypothesis is correct. Perhaps the. to fresh adult plumage. Colours variation observed in the morphs 1S become faded and dull on worn birds under the control of more than one by the next spring and summer. See gene. Bent (1938) for excellent descriptions of plumages and molts in juven.iles, Gray Morph first year birds and adults. Partial and The gray morph is the most common total albinos are known in this morph in Ontario and throughout the species [Holt et al. 1995). northern part of the Eastern Screech- ONTARIO BIRDS AUGUST 1995 69 Frequency of Eastern Screech-Owl Morphs 400 1\ 350 Gray 300 \ 250 \ Red! 200 \ 150 \ / ~ Brown / 100 <, Intermediate / 50 <; J o I I I I I 2 3 4 5 6 Figure 2: Data from Table 1 in Owen (1963). Owl's range. See Figure 1. Based on specimens in the Royal Ontario specimens in the Royal Ontario Museum (Martin 19501- Museum, Martin (1950) reported that Red birds are uncommon in the 81 percent of the population in northern parts of the screech-owl's Ontario was of the gray morph. range. Why? The reason may be that Martin did not recognize a brown red morph birds have a lower morph, apparently lumping gray and survival rate than gray birds during brown birds in his study. Gray unusually cold and severe winters. morph birds in fresh plumage in fall Plumage colour is correlated with are a clear gray, becoming tinged thermal adaptation. Mosher and with brown on worn and faded birds Henny (1976) found under laboratory in spring and summer (Kaufman conditions at _5° C and _10° C that 1990). Typical brown morphs are a red birds had significantly higher richer cinnamon-brown colour, metabolic requirements than gray including the facial disc. birds. Differential mortality was observed in an Ohio study by Red Morph VanCamp and Henny (1975). They Red morph screech-owls are bright, report that 44 percent more red birds "a gorgeous rufous like a red fox" died than gray birds during the (Marshal! 1967). Red morphs particularly severe winter of comprise about 19 percent of the 1951-1952. Perhaps the percentage of Ontario population, based on red birds declined in southern VOLUME 13 NUMBER 2 70 Ontario during the winter of as "very beautiful indeed. The overall 1993-1994, one of the snowiest and coloration was dry gray-brown, with coldest winters on record! Similarly, highlights of bright rufous-reddish Gullion and Marshall (1968) in areas on the scapulars and breast Minnesota found a differential feathers". Kay McKeever (pers. mortality between red and gray comm.) of The Owl Foundation in morph Ruffed Grouse (Bonasa Vineland describes the brown morph umbellus) related to winter survival. as a "warm brown like a saw-whet Why red coloration is linked to owl". Ross James (in litt.) of the winter survival in these two species Royal Ontario Museum says "there is is unknown. considerable variation in the brown There are two additional coloration depending on whether it differences between gray and red tends towards reddish or grayish. In general, the brown is more of a morph birds that are noteworthy. First, Kay McKeever (pers. comm.) cinnamon or tawny brown as reports that "the feathering on the opposed to a dark chocolate, legs of red birds appears to be less reflecting a mix of reddish tones on dense than on grays". Second, red one side and lighter or whiter gray on birds spend more time in cavities the other". In New England the during cold winter days, 80 percent brown morph is described as being (red) versus 38 percent (gray) (Voous chocolate brown in colour (Smith 1988). Bruce Di Labio (pers. comm.) 1993). but intermediate birds from reported that the red bird of a mixed Ontario in the ROM are not chocolate pair he observed for many years in brown (Ross James, pers. comm.). Ottawa often was more difficult to Similarly, Kay McKeever (pers. find in winter than the gray bird. comm.) has never seen a chocolate brown Eastern Screech-Owl. Brown Morph Be aware that brown morph The brown or intermediate morph is screech -owls could be overlooked as by far the least common form in gray birds given only a frontal screech -owl populations, except in (ventral) view.
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