Northern Harrier (Circus cyaneus)
Associated Species: Other species that may use habitat in a similar way and/or respond similarly
to threats, management, and conservation activities include Virginia Rail, Sora, Common Snipe,
Short-eared Owl, Marsh Wren, Red-winged Blackbird, and Yellow-headed Blackbird.
Distribution: Northern Harriers breed in North America and Eurasia. They breed throughout
North America except for the South and Southeast, with their highest densities occurring in the
northern prairie regions (Price et al. 1995). They reside throughout Colorado, with highest
densities on the eastern plains, mountain parks, and western valleys.
Habitat Requirements: Northern Harriers breed in a wide array of habitats, but they typically
prefer large tracts (100 ha; 250 ac) of wetlands with dense vegetation. Actual breeding habitat
preferences may be fairly broad, and include wet meadows, grasslands, sandsage prairie, and
croplands, but little information is available. This species has a large home range (Craighead and
Craighead 1956), which makes the researcher's task of locating nests difficult.
Ecology: In Colorado Northern Harriers initiate breeding in late April, and young leave the nest
by August. These hawks feed on small mammals, birds, reptiles, and amphibians. They hunt by
flying low over wetlands, grasslands, shrublands, and croplands. Their keen sense of hearing and
sight make this low altitude strategy successful.
Management Issues and Conservation Recommendations: The population of Northern
Harriers has declined due to wetlands habitat losses. Large feeding areas are needed. Identify
and protect larger wetlands used by this species. Erect buffers to incompatible land uses such as
In wetlands where water levels are regulated, nests become flooded by sudden rises in water
levels. Do not allow water levels to rise more than 15 cm (6 in) during the nesting season.
Large numbers of livestock permitted to graze in wetlands during the breeding season may
accidentally trample nests or young. Stock wet meadows and wetland pastures at low levels.
Habitat management schemes for waterfowl and upland game birds generally benefit harriers.
Managers should continue to consider the potential benefits and impacts of such management to
Loss of prey species, either through direct control or through habitat loss, reduces populations.
Maintain populations of voles at levels compatible with economic uses of the land.
Some nests are destroyed by agricultural equipment. Postpone haying until after the end of
nesting, or avoid the area immediately around harrier nests.
Status and Reasons for Concern: This species has a moderately high conservation need
throughout its range, along with high representation in the physiographic area and a declining
population trend. BBS data from Physiographic Area 36 during 1966-1996 reveal a statistically
significant annual rate of decline (-4.6%; P = 0.07; n = 35 routes). The Northern Harrier was
present on an average of 32.94% (SE = 2.60) of BBS routes run in Physiographic Area 36 in
Colorado during 1988-1997, at an average abundance of 0.65 (SE = 0.08) 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 of the
BBS and MCB monitoring programs.
Selected References: Andrews and Righter 1992, Kingery 1998, MacWhirter and Bildstein