Cooper's Hawks (Accipiter cooperii) from approximately the northern third of the species' breeding range are considered migratory, hawks in the central portion are either migratory or resident, and hawks farther south are believed to be nonmigratory. We compared long-distance movements (>100 km between natal nest and encounter location) of Cooper's Hawks banded as nestlings at two different ranges of latitudes (>35° and <35°N). Our goal was to determine whether long-distance movements indicate that Cooper's Hawks from southern latitudes (south of 35°N) are migratory and whether any migrate north, as do Bald Eagles (Haliaeetus leucocephalus) from several locations in the southern U.S.A. and Red-tailed Hawks (Buteo jamaicensis) from southern California. Long-distance movements by hawks banded as nestlings north of 35°N were strongly oriented to the south, with only 17% in a northerly direction. The only hawks encountered >100 km from nests south of 35°N were from southern Arizona and southern California. As opposed to the strong southward orientation of long-distance movements of hawks from north of 35°N, mean direction south of 35° was bipolar. Northward long-distance movements from nests in southern Arizona were relatively short (<200 km), while southward movements were substantially longer (1637 km in one case). Three Cooper's Hawks from southern Arizona were encountered in central Mexico, well south of the known breeding range, which suggests some individuals from southern Arizona are migratory. The pattern of long-distance movements from southern California was the reverse of that from southern Arizona. Most long-distance movements toward the south from southern California nests were comparatively short, whereas the three longest movements from that area (616–993 km) were to the north. Although tentative, we believe these longer movements are indicative of northward migration rather than natal or breeding dispersal.
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Vol. 51 • No. 4