Brewer's Sparrow (Spizella breweri)
Associated Species: Other species that may use habitat in a similar way and/or respond similarly
to threats, management, and conservation activities include Sage Grouse, Sage Thrasher, Green-tailed Towhee, and Sage Sparrow.
Distribution: The distribution of Brewer's Sparrows generally coincides with the distribution of
sagebrush in the West, from east central British Columbia, southeast to southwestern
Saskatchewan, then south to southern California and east to central New Mexico. A disjunct
population in the Yukon Territory and northwestern British Columbia may be a separate species.
In Colorado in Physiographic Area 62, Brewer's Sparrows are concentrated in mountain parks in
the north (especially North Park) with smaller concentration in the northeast, and the San Luis
Habitat Requirements: Brewer's Sparrows are tied closely to sagebrush, where it breeds in tall,
dense stands or stands broken up by grassy openings. They also nest in other shrubs, such as
willows, mountain mahogany, rabbitbrush, and snowberry. These sparrows prefer an abundance
of shrub cover: within a given habitat patch, their probability of occurrence increases with
increases in total shrub cover.
Ecology: These birds arrive in Colorado in mid to late April, and nesting begins by mid May.
Most young fledge in June and July. Most birds have left the state by early October, en route to
their wintering grounds in the southwestern states and Mexico. Their diet consists of insects,
spiders, grass and forb seeds.
Management Issues and Conservation Recommendations: Brewer's Sparrows suffer habitat
loss due to removal of sagebrush, usually for conversion to housing or to improve forage for
livestock or wildlife. Treatment of large areas of sagebrush with herbicides causes individuals to
abandon the treated area (Schroeder and Sturges 1975). Prescribed burns that remove no more
than 50% of the sagebrush may result in a decline in local Brewer's Sparrow populations for 1-2
years, but populations should rebound after that (Petersen and Best 1987). These sparrows prefer
large, contiguous sagebrush stands; the minimum acceptable stand size has not been determined
but isolated stands of sagebrush smaller than 2 ha (5 ac) are not likely to be nesting habitat (Knick
and Rotenberry 1995). Maintain contiguous sagebrush stands of at least 12 ha (30 ac).
Status and Reasons for Concern: This species is on the national Watch List, indicating a high
conservation need throughout its range. Within Physiographic Area 62, BBS data do not show a
statistically significant annual rate of change between 1966 and 1996 (P = 0.28; n = 21 routes).
However, BBS data for the same period indicate a significant, survey-wide annual rate of decline
(-3.7%; P < 0.01; n = 397 routes). Brewer's Sparrows were present on an average of 27.55%
(SE = 2.52) of the BBS routes run in Physiographic Area 62 in Colorado during 1988-1997, at an
average abundance of 2.18 (SE = 0.41) individuals per route. The mean number of routes run
each year was 21.1 (SE = 3.06). This species is monitored by MCB with point transects.
Biological Objective: Maintain or increase the species' distribution and abundance, based upon
results of the BBS and MCB monitoring programs.
Selected References: Andrews and Righter 1992, Kingery 1998, Rotenberry et al. 1999, Paige
and Ritter 1999, Short 1984.