Swainson's Hawk (Buteo swainsoni)
Associated Species: Other species that may use habitat in a similar way and/or respond similarly
to threats, management, and conservation activities include Red-tailed Hawk, Ferruginous Hawk,
Rough-legged Hawk, Golden Eagle, American Kestrel, Mourning Dove, Great Horned Owl, and
Distribution: Swainson's Hawks breed from central Alberta east to southern Manitoba and
western Minnesota, south through Texas to the Mexican states of Sonora and Durango, and west
to southern California. In Colorado, they breed throughout the eastern plains in the grassland and
lowland riparian habitat types. They are also found in North and South Parks, the San Luis
Valley, and sparsely in western valleys and grassland parks. Swainson's Hawks winter in
southern South America.
Habitat Requirements: Swainson's Hawks nest in riparian areas adjacent to grasslands and in
trees or large shrubs standing in open shrublands or croplands. They also nest in trees planted in
shelterbelts or farmyards. The adjacent open habitats are used for foraging.
Ecology: Swainson's Hawks reside in Colorado from April into October. Nest construction
takes place during the latter half of April through May, and young fledge during June and July.
The breeding season diet consists primarily of small mammals such as ground squirrels, pocket
gophers, mice, and voles, but also includes reptiles and large invertebrates such as grasshoppers
Management Issues and Conservation Recommendations: Populations of this species may
have benefitted from human settlement of the Great Plains as trees planted as windbreaks and
around homesteads provide nesting substrate. Many of these trees are being lost through
senescence and through active removal as small farms are consolidated into larger farms and
homesteads are removed. Also, government incentives to plant trees for windbreaks have largely
disappeared. As a result, the Great Plains are probably experiencing a net loss of trees. Preserve
trees in shelterbelts, windbreaks, and around homesteads, especially those trees that already
Programs to control the principal prey species are probably detrimental to Swainson's Hawk
populations, as a declining prey base has been linked to diminished reproductive success. Retain
populations of the principal prey species (rodents and grasshoppers) at levels compatible with
economic activities on the land.
In Argentina, agricultural use of organophosphate insecticides has resulted in deaths of large
numbers of wintering birds due to direct exposure and consumption of poisoned grasshoppers.
Although the most notorious of the insecticides (monocrotophos) has been banned, other
organophosphate insecticides remain in use. Encourage adoption of alternatives to
organophosphates on the wintering grounds.
Status and Reasons for Concern: This species has a high conservation need locally and
throughout its range. Within the shortgrass physiographic area, BBS data do not show a
statistically significant annual rate of change between 1966 and 1996 (P = 0.40; n = 56 routes).
Swainson's Hawks were present on an average of 85.38% (SE = 0.98) of the BBS routes run in
Physiographic Area 36 in Colorado during 1988-1997, at an average abundance of 3.69 (SE =
0.21) 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 species' distribution and abundance, based upon results from
the BBS and MCB monitoring programs.
Selected References: Andrews and Righter 1992, Bechard 1983, England et al. 1997, Kingery