Breeding Habitat:Grassland
Nest Type:N/A
Migration Status:Short distance migrant
Nest Location:N/A
Breeding Northern Harriers generally inhabit marshlands, wet meadows, and other damp grassland habitats across the northern United States and Canada, but are also occasionally found in upland fields (Bildstein 1988). As is true for most raptors, harriers are recorded in relatively small numbers along BBS routes throughout their range. They appear to be most numerous in the northern Great Plains from the Dakotas and Montana into southern Canada (Relative Abundance Map). Scattered records from the southern edge of the range may represent late migrants or nonbreeders.
Populations of Northern Harriers have generally declined in the northeastern and midwestern United States throughout the twentieth century, primarily as a result of habitat destruction and the more intensive agricultural use of remaining grasslands (Serrentino and England 1989, Sweet 1991). Trends in the western United States are poorly known, but harrier populations are believed to be stable or slowly declining in most states (Martin 1989). Similar trends are apparent on the BBS, where the most consistent declines occur on the Great Plains from Oklahoma to southern Canada (Trend Map).
During 1966-1994, harrier populations have declined in the Central BBS Region and across the United States. Declines within states/provinces and physiographic strata are concentrated on the Great Plains (Trend List). Increasing populations occur in Wisconsin and the Eastern BBS Region. Population declines were most evident prior to 1980 when they occurred in seven states/provinces and four physiographic strata. Only North Dakota had an increasing population during 1966-1979. Since 1980, harriers have declined in Canada, three states/provinces, and one strata, while there are increases in one state/province and one strata. These trend data apply only to harriers breeding in the United States and Canada; populations in arctic Canada and Alaska are not currently monitored by the BBS.
Breeding populations are known to exhibit considerable annual fluctuations in response to the abundance of prey (Bildstein 1988). These annual fluctuations are not apparent in the survey-wide indices, because few harriers are recorded on most BBS routes (Survey-wide Annual Indices). However, these fluctuations are more apparent in the indices for states/provinces and physiographic strata. For example, harriers in Alberta underwent noticeable population fluctuations through the mid-1980s, but have been fairly stable subsequently (Alberta Annual Indices). North Dakota exhibits similar fluctuations throughout the survey period, with a slight increasing tendency in its populations (North Dakota Annual Indices). A similar pattern occurs in Oregon (Oregon Annual Indices). South Dakota populations have also fluctuated as they declined (South Dakota Annual Indices). In contrast, the declining population in Minnesota exhibits few marked fluctuations in abundance (Minnesota Annual Indices).
Wintering Northern Harriers are widely distributed across the U.S. and southern Canada. On CBCs, they are most numerous along the southern Great Plains from Kansas into Texas and throughout the Great Basin region. Their population trends are mixed, with significant declines slightly outnumbering increases. Declining populations are most evident in central North America, while increases are scattered throughout its range.
Bildstein, K.L. 1988. Northern Harrier. Pp. 251-303 in R.S.
Palmer, ed. Handbook of North American birds. Vol. 4:
diurnal raptors, part 1. Yale Univ. Press, New Haven, CT.
Martin, J.W. 1989. Harriers and kites. Pp. 92-101 in B.G.
Pendleton, ed. Proceedings of the western raptor management
symposium and workshop. Natl. Wildl. Fed. Scien. Tech. Ser.
No. 12.
Serrentino, P., and M. England. 1989. Northern Harrier. Pp. 37-
46 in B.G. Pendleton, ed. Proceedings of the northeast raptor
management symposium and workshop. Natl. Wildl. Fed. Scien.
Tech. Ser. No. 13.
Sweet, M.J. 1991. Kites and Northern Harrier. Pp. 32-41 in B.G.
Pendleton and D.L. Krahe, eds. Proceedings of the midwest
raptor management symposium and workshop. Natl. Wildl. Fed.
Scien. Tech. Ser. No. 15.