Snyder, N.F.R.; Wiley, J.W. (1976). “Sexual size dimorphism in hawks and owls of North America”. Ornithology Monograph. The American Ornithologists' Union (20): i–96. doi:10.2307/40166710. JSTOR40166710.
Snyder, N.F.R.; Wiley, J.W. (1976). “Sexual size dimorphism in hawks and owls of North America”. Ornithology Monograph. The American Ornithologists' Union (20): i–96. doi:10.2307/40166710. JSTOR40166710.