Ferruginous Hawk Nesting Ecology and Raptor Populations in Northern South Dakota

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Abstract
The breeding ecology of the ferruginous hawk was studied in north-central South Dakota [USA] in the spring and summer of 1973 and 1974. Notes on other raptors of the 269-km2 study area were also kept. The ferruginous hawk population averaged 1 pair/17.4 km2 and the total raptor population was estimated at 1 pair/11.2 km2. Ferruginous hawks nested on the ground, on haystacks, and in trees. Ground nests were generally found in remote areas within large prairie tracts in high condition. Tree nests were found in both cultivated and prairie sites and not necessarily in remote areas. However, the prairie is an important component within all territories as it provides habitat for prey species. The average clutch of 4.3 eggs was substantially larger than those previously reported. The large clutches may have resulted from the abundance of Richardson''s ground squirrels, the principal prey species on the study area. Nest hatching success for the 2 yr was 63%, and an average of 1.5 young were fledged for each resident pair. At this level of recruitment, ferruginous hawks in the area apparently fledged adequate young to maintain population stability. A large proportion of the ground nests were lost to predation.

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