Land Bird Conservation Plan Colorado  

Overview of Colorado
Physiographic Region 36

  • Grasslands
  • Lowland Riparian
  • Shore/Bank
  • Wetlands

  • Physiographic Region 62
    Physiographic Region 87
    Implementation Strategies
    Literature Cited

    Physiographic Region 36: Central Shortgrass Prairie

    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 Loggerhead Shrike.

    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 and beetles.

    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 contain nests.

    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 1998.

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