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

Habitat

Habitat Requirements

Burrowing Owls nest in open country, such as grazed pastures, prairie grasslands, sometimes with small amounts of sagebrush, and the edges of agricultural fields (Poulin et al. 2005). In all of these habitats, owls prefer to nest in areas with sparse vegetation and flat, open terrain. In Canada, Burrowing Owl habitat in Alberta and Saskatchewan is typically flat, treeless prairie, while in British Columbia preferred habitat is plateau and valley grassland (Wellicome and Haug 1995). Another important habitat component for Burrowing Owls is proximity to land with medium to tall grass for (largely nocturnal) foraging. While owls typically restrict their diurnal foraging to the area in the immediate nest vicinity, they appear to range more widely at night, feeding over nearby fields in denser vegetation (Haug and Oliphant 1990, Plumpton 1992, Sissons et al. 2001, Sissons 2003.).

In Canada, nests are always in abandoned burrows of various mammals, including ground squirrels, prairie dogs, badgers, foxes, skunks, coyotes, and marmots (Wellicome and Haug 1995, Wellicome 1997, Poulin et al. 2005), or in artificial nest burrows (De Smet 1997, Wellicome et al. 1997, Leupin and Low 2001). Burrowing Owls typically nest in whichever burrow type is most common locally. On the Great Plains, owls appear to show a preference for nesting in active prairie dog towns (e.g., Butts and Lewis 1982), and owl abundance may be linked to the local abundance of prairie dogs (Desmond et al. 2000). In Canada, most populations of Burrowing Owls now nest in abandoned badger and Richardson’s ground squirrel (Spermophilus richardsonii) burrows, but show a preference for burrows with entrances that are ‘badger-sized’ (Poulin et al. 2005).

Burrowing Owls typically spend the day close to their nest burrow and fly further from the burrow area at night to forage (Haug & Oliphant 1990). Reported mean home-range sizes for Burrowing Owls are 2.41 km2 in Saskatchewan (Haug and Oliphant 1990) and 3.73 km2 in Alberta (Sissons 2003). Sissons (2003) showed that Burrowing Owls spend considerable time foraging at night in nearby grassland areas. Home-range size shows a positive correlation to the percentage of surrounding habitat that is under agricultural cultivation,,suggesting that larger home-ranges are required when higher proportions of land are under cultivation (Haug 1985, Wellicome and Haug 1995).


Habitat Trends

Suitable breeding, migration, and wintering habitat (primarily open grassland) continues to decline (see Telfer 1992, Hjertaas 1997, Warnock and Skeel 2004). Telfer (1992) estimated a loss of 39% of the native grasslands in prairie Canada between 1949 and 1986. Hjertaas and Lyon (1987) estimated a 21% loss of native prairie in Saskatchewan over a 7-year period in the late 1970s and early 1980s. In Manitoba, at least 20% of historic nest sites recorded over a five-year period were destroyed during land cultivation or urban development (Haug and Churchward 1988). Warnock and Skeel (2004) reported that grassland loss, specifically from owl sites in southern Saskatchewan, averaged 6% per year from 1987 to 1993. All of these studies suggest that the primary loss of habitat occurs through conversion of native grasslands to agricultural crops.

In Canada, the rate of loss of grassland habitat has been accompanied by a decline in the number of ground squirrels and an even more rapid decline in the abundance of Burrowing Owls. In British Columbia, Howie (1980) identified a reduction in badger (Taxidea taxus jeffersonii) populations as the main factor responsible for the provincial Burrowing Owl decline. On the prairies, there are indications that Richardson’s ground squirrels have decreased in some parts of Alberta (Kirk and Banasch 1996), Saskatchewan (Schmutz et al. 2001), and Manitoba (K. De Smet, pers. comm.), but population data are not available at larger scales (Michener and Schmutz 2002). The population of Burrowing Owls in the four western provinces is now so low that areas of potentially suitable habitat are not currently occupied (Skeel et al. 2001, Burrowing Owl Recovery Team Meeting, 2004).


Habitat Protection/Ownership

The majority of suitable Burrowing Owl habitat in Canada is under private ownership. As a consequence, habitat protection programs have been initiated with voluntary land stewardship programs including Operation Grassland Community (http://www.afga.org/Conservation/ogc.htm) in Alberta and Operation Burrowing Owl (http://www.naturesask.com/OBO/obo.htm) in Saskatchewan. These programs encourage landowners to report the number of Burrowing Owls on their land each year, to protect nesting areas from cultivation and pesticide use, and to consider planting native grasses in place of introduced grass species. Both programs have been successful in raising the profile of native species, have helped efforts to retain native grasslands (e.g., Warnock and Skeel 2004), and have also contributed valuable long-term data to Burrowing Owl monitoring efforts.

There are currently efforts underway in Alberta and Saskatchewan (T. Wellicome, pers. comm., September 2004) to first identify and then to protect (with stewardship and conservation easements) critical habitats for breeding Burrowing Owls. Habitat protection on the migration routes (U.S.A.) and on the wintering grounds (Mexico) is also critical because recovery of the Canadian population may also be dependent on habitat conservation measures in these areas.