Cassin's Sparrow (Aimophila cassinii)
Associated Species: Other species that may use habitat in a similar way and/or respond similarly
to threats, management, and conservation activities include Scaled Quail, Loggerhead Shrike, and
Distribution: Cassin's Sparrows breed in areas from northeastern Colorado and southeastern
Wyoming east to west-central Kansas, south through Texas to northern Tamaulipas, and
northwest to southeastern Arizona. Within Colorado, they nest throughout the eastern plains
with highest concentrations in the southeast. They winter in southern Arizona, New Mexico, and
southern Texas, south to central Mexico.
Habitat Requirements: These sparrows inhabit shortgrass prairie with scattered shrubs
(including sand sagebrush, yucca, and rabbitbrush), which they use for song perches and nest
cover. Breeding birds will accept a wide range of shrub densities as long as grass cover exists.
Ecology: Cassin's Sparrows arrive in Colorado in early to mid April, but most do not initiate
nesting until late May. Incubation and brooding take place in June, and most young fledge by mid
July. Most birds have left for their wintering grounds by late September. The diet consists of
invertebrates (beetles, grasshoppers, crickets) and seeds.
Management Issues and Conservation Recommendations: Local populations of Cassin's
Sparrows exhibit extreme annual fluctuations, especially in peripheral areas of the range such as
Colorado. Populations appear to move around in response to precipitation patterns, most likely
because they affect vegetation growth, grass seed production, and invertebrate populations.
Public land managers and private landowners should be encouraged to create a landscape
mosaic of grassland parcels of different heights and densities to provide Cassin's Sparrow
populations options for establishing breeding sites each year.
Heavy grazing can remove grass cover needed by breeding Cassin's Sparrows, especially in arid
regions where grasses are naturally short and sparse. However, in less arid parts of its range, this
species regularly utilizes grazed areas. This topic needs further study. Fire can also remove grass
cover and shrubs, and render the habitat unsuitable for Cassin's Sparrows until the vegetation
recovers--up to two growing seasons in arid regions. Graze lightly (or avoid grazing) in areas
of short, sparse grasses. Where prescribed burns are used as a management tool, burn habitat
blocks in rotation, so that unburned blocks are always available.
Status and Reasons for Concern: This species is on the national Watch List, indicating a high
conservation need throughout its range. A high proportion (estimated at 17.0%) of its total
population occurs within this physiographic area, indicating that this area has high responsibility
for the species' conservation. Within the Central Shortgrass Prairie, BBS data do not show a
statistically significant annual rate of change between 1966 and 1996 (P = 0.15; n = 31 routes).
However, for the same period, BBS data reveal a significant survey-wide decline (-2.5% per year;
P < 0.01; n = 203 routes). Cassin's Sparrows were present on an average of 72.36% (SE = 3.07)
of the BBS routes run in Physiographic Area 36 in Colorado during 1988-1997, at an average
abundance of 33.54 (SE = 3.18) individuals per route. The mean number of routes run each year
was 29.2 (SE = 2.28). This species is monitored by MCB with point transects.
Biological Objective: Increase the distribution and abundance of the species, based upon results
of the BBS and MCB monitoring programs.
Selected References: Andrews and Righter 1992, Bock and Webb 1984, Dorn and Dorn 1995,
Faanes et al. 1979, Hubbard 1977, Kingery 1998.