35. MacWhirter, B., and K. L. Bildstein. 1996. Northern Harrier (Circus cyaneus). Number 210 in The birds of North America, No. 210, A. Poole and F. Gill, editors. The Academy of Natural Sciences and the American Ornithologists' Union, Philadelphia, Pennsylvania, and Washington, D. C. | Hawk Mountain Sanctuary: Learn Visit Join

35. MacWhirter, B., and K. L. Bildstein. 1996. Northern Harrier (Circus cyaneus). Number 210 in The birds of North America, No. 210, A. Poole and F. Gill, editors. The Academy of Natural Sciences and the American Ornithologists' Union, Philadelphia, Pennsylvania, and Washington, D. C.

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