Martell, Mark, and Ted Dick. 1996. Nesting Habitat Characteristics of the Northern Goshawk (Accipter gentilis) in Minnesota. Final report to the Minnesota Department of Natural Resources, Nongame Wildlife Program. http://files.dnr.state.mn.us/eco/nongame/projects/consgrant_reports/1996/1996_martell_dick_nolocations.pdf