Hybridization between Barred and Spotted Owls

Autor: Thomas E. Hamer, A. D. Fuchs, M. L. Walters, Eric D. Forsman
Rok vydání: 1994
Předmět:
Zdroj: The Auk. 111:487-492
ISSN: 1938-4254
0004-8038
Popis: Interspecific hybridization has been reported in at least 52 of 516 nonmarine bird species in North America (Johnsgard 1970, Mayr and Short 1970, Short 1965, 1972). It tends to occur infrequently, however, except where allopatric species are brought into contact by range expansions (Cade 1983). Groups in which interspecific hybridization is particularly common include warblers, grouse, and hummingbirds (Mayr and Short 1970, Oliphant 1991). Instances of interspecific hybridization in birds of prey are uncommon except in captivity (Newton 1979, Cade 1983, Oliphant 1991). In owls, interspecific hybridization appears to be rare. Johnsgard (1988) reported instances of hybridization between Eastern Screech-Owls (Otus asio) and Western Screech-Owls (0. kennicottii) in Texas, and Voous (1989) reported instances of hybridization between Whiskered Screech-Owls (0. trichopsis) and Western Screech-Owls in Arizona. Evidence of hybridization in the genus Strix has been limited to Ural Owls (S. uralensis) hybridizing with Tawny Owls (S. aluco) in captivity (Mikkola 1983). We present the first records of hybridization between the Northern Spotted Owl (S. occidentalis caurina) and Northern Barred Owl (S. varia varia), two species that are thought to be closely related and that have recently become sympatric (Grant 1966, Taylor and Forsman 1976, Hamer 1988). Since at least the early 1950s, the Barred Owl has been expanding its range into western North America. In the process, it has invaded much of the historical range of the Spotted Owl (Grant 1966, Taylor and Forsman 1976, Hamer 1988). Barred Owls are now common in forested areas in southwestern British Columbia and northern Washington (Hamer 1988, Dunbar et al. 1991), and they are rapidly increasing in Oregon and northern California. Increasing sympatry between Barred and Spotted owls has led to speculation that the Northern Spotted Owl, which is listed as a threatened species (U.S. Fish and Wildlife Service 1990), may be further threatened by competition with the Barred Owl, as well as by habitat loss (Taylor and Forsman 1976, Dunbar et al. 1991). The possibility that sympatry might also result in hybridization between the two species has not been previously considered. Records of hybrids.-Three adult Spotted Owl/Barred Owl hybrids, two in Washington and one in Oregon, were confirmed during 1989-1992, and one juvenile hybrid was produced by a female Barred Owl paired to a yearling male Spotted Owl in Oregon in 1992. All hybrids were identified by their unique plumage characteristics, vocalizations, and measurements. The first hybrid was an adult male seen on 23 March 1989 at Baker Lake in the Washington Cascades Range, 30 km south of the United States/Canadian border. This bird was fitted with a radio transmitter in 1989 and recorded in the same area in spring 1990, 1991, and 1992. Its nesting status was not determined, but it was always seen with a female Barred Owl. Both birds aggressively defended the territory in response to playback calls. The second hybrid, an adult male located in the Klamath Mountains 29 km northeast of Medford, Oregon, in 1990 was paired with a female Barred Owl. This pair produced two young in 1990 and three young in 1991. In 1992 the Medford hybrid was displaced by a male Barred Owl. It was relocated in June 1992, 1 km from its previous nesting site and did not appear to be paired (James Harper pers. comm.). Another suspected hybrid (or possibly the same individual) was seen and heard in this area in 1987 (James Harper pers. comm.). The third hybrid was an adult female observed several times in May 1991, 2 km south of Ozette Lake, Washington, near the northwestern tip of the Olympic Peninsula. When this bird was captured, we found that it had been banded as a juvenile in 1986, 277 km to the southeast in the Cascade Range of southern Washington. The original bander suspected that the bird may have been a hybrid, but was unsure because it was not fully feathered and because both parents were not observed (H. Allen pers. comm.). When located in 1991, the Ozette Lake female was paired with an adult male Spotted Owl. No young were observed, but the female had a brood patch that was regressing, which suggested that nesting may have been attempted. Both birds were observed together in 1992 when nesting was again attempted but failed for unknown reasons. In addition to the three adult hybrids described above, a fourth hybrid from a pairing between a Barred Owl and Spotted Owl was confirmed in 1992 in Douglas County, Oregon, 8 km southeast of Canyonville. This pair consisted of a yearling male Spotted Owl and an adult female Barred Owl. They produced one young, which was first observed on 1 June 1992. The F, hybrid juvenile was fitted with a tail-mounted radio
Databáze: OpenAIRE
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