Asio flammeus
Breeding Habitat:Grassland
Nest Type:N/A
Migration Status:Short distance migrant
Nest Location:N/A
A resident of mixed and tall grass habitats throughout the year, the Short-eared Owl is a nomadic species that tends to congregate in areas where vole populations are high. Hence, the numbers of breeding and wintering owls may fluctuate markedly from year to year, depending upon the availability of their rodent prey (Clark 1975). While these population fluctuations may partially obscure long-term trends, in general Short-eared Owl populations have declined in North America since 1900. These declines are very evident in the northeastern states, where Short-eareds have become one of the rarest and most threatened species (Melvin et al. 1989). However, similar trends have been reported from Ontario (Cadman et al. 1987) to North Dakota (Stewart 1975) and Colorado (Andrews and Righter 1992).
Along BBS routes, Short-eared Owls are generally reported in small numbers across central and western North America. Very few are found in the eastern portion of their range (Relative Abundance Map). The year-to-year fluctuations in abundance and variable counts along many routes result in relatively imprecise trend estimates for many populations. Over the entire survey period, breeding populations have declined in Alberta, the Aspen Parklands (S30) stratum, Western BBS Region, and Canada (Trend List). The trends during 1966-1979 tend to be imprecise and based on small sample sizes, but indicate increases in the Central BBS Region and declines in Canada and the Western BBS Region. All trend estimates are non-significant after 1980. The trend map shows a mixture of increases and declines across the northern Great Plains and northern Rocky Mountains (Trend Map). The low relative abundance of Short-eared Owls along most routes tends to obscure any temporal patterns in the survey-wide trends, although a slight decline is indicated since the 1960s (Survey-wide Annual Indices). Variable counts and small sample sizes preclude analyses of temporal patterns in the trends of regions, states/provinces, and strata.
Short-eared Owls are generally recorded in small numbers throughout their range on CBCs. Trend estimates based on these data are generally in a negative direction, and all significant trends are declines. These declining populations occur in all portions of the winter range.
As is true for most grassland birds, habitat loss is believed to be the primary factor responsible for the declines of Short-eared Owls (Marti and Marks 1987, Melvin et al. 1989). Overgrazing may also be a factor, especially in western North America.