Spotted owl (Caurina subspecies) COSEWIC assessment and status report: chapter 3

Species Information

Name and classification

Scientific name:
Strix occidentalis caurina Xántus 1859
English name:
Spotted Owl
French name:
Chouette tachetée
Classification:
Class – Aves
Order – Strigiformes
Family – Strigidae
Genus – Strix
Species – occidentalis
Subspecies – caurina

Classification follows the American Ornithologists’ Union (AOU 2005). First described by Xántus (1859), there are now three widely recognized subspecies (Dawson et al. 1986), which are based mainly on range and morphological variations (slight differences in size and plumage colouration): the Mexican Spotted Owl (Strix occidentalis lucida Nelson 1903), the California Spotted Owl (Strix occidentalis occidentalis Xantus 1859) and the Northern Spotted Owl (Strix occidentalis caurina Merriam 1898). Recent genetic analyses have reconfirmed these subspecies (Haig et al. 2001; Courtney et al. 2004). Only the Northern Spotted Owl occurs in Canada.

The Spotted Owl is one of three Strix owl species in Canada; the other two are Great Gray Owl (Strix nebulosa) and Barred Owl (Strix varia).

Vernacular names: n/a

Morphological description

The Northern Spotted Owl is a medium-sized owl averaging 45 cm long and 90 cm wingspan. Plumage is dark overall with dark brown feathers patterned by small roundish pale spots over most of the body. The tail has white horizontal bars and there are no “ear” tufts. Eyes are large, dark brown and are set within lighter brown facial disks (Forsman 1981; Gutiérrez et al. 1995).

Age classes can be identified by differences in plumage characteristics. Juveniles < 5 months old are identified by visible down feathers (Forsman 1981). After 5 months, juveniles moult downy feather and look similar to adults. Sub-adult (1 - 2 years old) and adult (older than 2 years) owls may be identified by differences in tail feathers. Juveniles and sub-adults (1-2 years) have pointed tail feathers with white tips whereas adult tail feathers are rounded and usually mottled in colour (Forsman 1981). Male and females have similar plumage but females are about 15% larger (female mean weight = 663 g, male mean weight = 579 g, Blakesley et al. 1990).

Genetic description

Genetic structure analyses in the three geographically defined subspecies of Spotted Owl have been conducted on USA populations. Sequences (522 bp) from domains I and II of the mitochondrial control region were analyzed for 213 individuals from 30 local USA breeding areas. Results confirmed significant differences between Northern Spotted Owls and the other two subspecies but did not provide support for subspecific level differences between California and Mexican Spotted Owls. Divergence times for Northern and California/Mexican Spotted Owls were calculated to be 115,000–125,000 years ago. The genetic analysis showed a zone of contact between Northern and California Spotted Owls in California but the zone is stable with distinct subspecific haplotypes elsewhere in their respective ranges (Haig et al. 2004), presumably also including Canadian Northern Spotted Owls. These findings were different from a study that combined nuclear and mitochondrial analyses and concluded that Mexican Spotted Owls were genetically distinct from a genetically overlapping Northern/California Spotted Owl group (Barrowclough and Gutierrez 1990; Haig et al. 2001).

Mitochondrial DNA sequences indicated large divergence between the closely related Barred Owl (which is now hybridizing with Northern Spotted Owls) and Spotted Owls. Diagnostic AFLP bands indicated extensive genetic divergence between the species, including markers differentiating them. Hybrids have unique genetic combinations, including AFLP markers from both parental species. Most hybrids genetically sampled resulted from crosses between female Barred Owls and male Spotted Owls (Haig et al. 2004).

Designatable units

Not applicable.

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