Recoveries of Ferruginous Hawks Banded in Colorado

Recoveries of Ferruginous Hawks banded in Colorado Alan It. Harmata he Ferruginous Hawk (Buteo regalis) is currently designated a "Migratory Bird of High Federal Interest" (Stewart 1978) since a significant portion of its range is contained within maior coal producing regions of the West (Fig. 1).The species is also included on the "Blue List" of threatened birds (Arbib 1979), indicating that population size is substantially reduced from historical levels.Implicit in these designations is the need for more precise information concerning dispersal and migrational movements of this raptor especially from within potential or actual energy producing areas in the U.S.There is a paucity of information concerning movements of Ferruginous Hawks outside of their summer range.Lincoln (1936) reported recoveries of Ferruginous Hawks in California and more recently Thurow et.al. (1980) described sightings and recoveries of hawks color-marked and banded in an area of Idaho near a geothermal withdrawal site.Aside from Salt (1939) reporting recoveries of Ferruginous Hawks banded in Canada, little additional information is readily available concerning movements and mortality factors once the hawks leave their natal area.Thus, a study was initiated to determine local and long-range movements, wintering grounds, nest site fidelity, and primary mortality factors of a local population of Ferruginous Hawks.Study Area and Methods Between June 1973 and July 1976, 115 nestling (local) Ferruginous Hawks (Fig. 2) were banded in a 8733 km 2 section of Weld and Logan counties in northeastern Colorado.The area is typically rolling short grass prairie occasionally broken by bluffs, washes, buttes, and wooded stream bottoms and is contained in the Denver --Raton Mesa Coal Producing Region (Fig. 1).Active resource exploitation is not current but exploration for coal, uranium, natural gas, and other resources is underway.Although this section of the Great Plains is considered to be on the southeastern edge of the breeding range of the Ferruginous Hawk (Snow 1974), nesting density is high.Olendorff (1973) found 1 nesting pair per 100 km 2, second in density only to the very common Swainson's Hawk (Buteo swainsonii).Bent (1927) and Bailey and Niedrach (1965) considered the Ferruginous Hawk a common summer resident and a casual or less common winter resident in northeastern Colorado.Active Ferruginous Hawk nests were found by inspecting historical sites and by searching cliffs, power poles, and erosional remnants for new nests.As Ferruginous Hawks are reported to be sensitive to human disturbance (Olendorff arid Stoddart 1974; White et.al. 1979) which may result in abandonment of eggs or young, nest searches were delayed until early June when 2 to 4 week old young were usually present.Nestling hawks were banded with USFWS lock-on bands usually between the ages of 25 and 30 days.The

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