Probable Identity of Purported Rough-Legged Hawk Nests in the Western U.S. and Canada

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The oological record of the Rough-legged Hawk (Buteo lagopus) is puzzling. This panboreal species breeds north of 60?N latitude in tundra and taiga (Brown and Amadon 1968). In North America, it nests from coastal and arctic Alaska, east through the northern Yukon, coastal and in- terior Northwest Territories, to Quebec and Labrador, where it breeds in northern and coastal areas (Godfrey 1966, Zarn 1975, AOU 1983). In years when microtine rodents are abundant, these hawks are thought to irrupt farther south and to nest in small numbers in northern Manitoba (Taverner and Sutton 1934), southeastern Que- bec and Newfoundland, but never as far south as North Dakota and Montana. Nonetheless, at the turn of the cen- tury, oologists reported finding Rough-legged Hawks nest- ing in Colorado, Montana, and North Dakota, a full 1,000 km south of their presently accepted breeding range (Ar- nold 1895, 1897; Davy 1930a, b). Some of these records have been explained as incorrectly identified Ferruginous Hawk (B. regalis) nests (Taverner 1919). This seemed logical as Ferruginous Hawks were then commonly re- ferred to as "ferruginous rough-legs" or simply as "rough- legs," and they were common in areas where the more suspect nests were reported.