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COSEWIC assessment and update status report on the Burrowing Owl in Canada

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COSEWIC
Executive Summary

Burrowing Owl
Athene Cunicularia

Species Information

Burrowing Owls are small, long-legged predators of the open prairie with a close association with burrowing mammals such as ground squirrels (Spermophilus spp.), badgers (Taxidea taxus), and prairie dogs (Cynomys spp.). Adults are drably coloured with a mix of brown, white, and beige spotting. Juveniles are more richly coloured in dark brown and cream. Adults and young are relatively conspicuous because of their tendency to be active during the day, foraging from elevated mounds or fenceposts in open, prairie habitats.

Distribution

Burrowing Owls have a disjunct breeding distribution within Canada. A few (reintroduced) pairs breed in the Thompson-Nicola valley of southcentral British Columbia, while the main prairie population breeds from southcentral Alberta east through southern Saskatchewan. Available evidence suggests that the species is now essentially extirpated as a breeding species in Manitoba. In the United States, Burrowing Owls (A. c. hypugaea) breed from the Great Plains westward, with a disjunct subspecies resident in Florida (A. c. floridana). Burrowing Owls winter primarily in Mexico, with some birds overwintering in the southwestern United States (e.g., Texas, New Mexico, Arizona, California). The breeding range of Burrowing Owls in Canada has shrunk in recent years to less than half of the range occupied in the 1970s, and to only one-third of the range occupied in the early-1900s.

Habitat

Preferred habitat is open, sparsely vegetated grasslands with burrows excavated by badgers, ground squirrels, or other mammals. Foraging habitat is generally in and around nesting sites during the day, but at night, owls may forage further afield and in areas with denser grasses and forbs. On the wintering grounds, habitat includes open grasslands, agricultural fields, and scrubland.

Biology

Burrowing Owls return to Canadian breeding areas during April and May and nest in existing mammal burrows. In Canada, clutches are initiated in May with an average of 9 eggs (range = 5−14). Typically, a single brood is raised, although pairs that fail may lay a second (smaller) clutch. Family groups remain together until late August, then disperse to individual burrows before migrating southward in September and October.

Population Sizes and Trends

In Canada, the current (2004) minimum (known) population size is 795 individuals: 498 in Saskatchewan, 288 in Alberta, and 9 in British Columbia; this may underestimate the actual population by as much as 50%, so the population is likely between 800 and 1600 individuals. Only one pair has been confirmed breeding in Manitoba since 1999, and no nests were documented in Manitoba in 2004. Data from intensive and extensive Burrowing Owl surveys, as well as the Breeding Bird Survey, suggest a significant decrease in density in all areas of prairie Canada over the past 30 years, resulting in a 90% population decline from 1990 to 2000, slowing to a 57% decline from 1994 to 2004. In the U.S. portion of the range, populations of Burrowing Owls are thought to be stable in the core of the species’ range (e.g., Colorado, Idaho, New Mexico), but declining rapidly in California, in states along the eastern edge of the species’ range, and in the northern states that border Canada. Though population trends in Mexico are unknown, wintering owl populations have declined in Texas and California, where some of Canada’s population spends the winter.

Limiting Factors and Threats

Historically, the ultimate factor responsible for the decline in population viability of Burrowing Owls in Canada is thought to have been conversion of grassland to cropland, as well as the fragmentation and degradation of remaining grasslands. Other factors thought to have contributed to the recent population declines include: 1) higher emigration of owls from Canada to the U.S.A. than immigration to Canada from the U.S.A.; 2) loss of burrows (used for nesting and roosting) due to declines in the populations of burrowing mammals; 3) increased predation on the nesting grounds and in wintering areas resulting from increasing habitat fragmentation and changes in the predator community and grassland ecosystem; and 4) declines in prey abundance as a result of habitat changes and possibly changing weather patterns; 5) negative effects of toxins (from pesticide/herbicide applications); 6) mortality due to collisions with vehicles;

Special Significance of the Species

Burrowing Owls were once a common element of the prairie and southern interior (B.C.) landscapes. They are now rare throughout their Canadian range, and declining everywhere except in the core of their range in the U.S.A.

Existing Protection or Other Status Designations

Burrowing Owls are classified as G4 (apparently secure globally because of wide distribution, but some cause for concern due to declines) by NatureServe. Provincial NatureServe rankings are S1B in British Columbia and Manitoba, and S2B in Saskatchewan and Alberta. Burrowing Owls are listed as Endangered in Manitoba, Saskatchewan, Alberta, and British Columbia; it is listed as Endangered, Threatened or a Species of Concern in several U.S. states. The last COSEWIC designation classified Burrowing Owls as Endangered in Canada.