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1 June 2000 AGE AND SEX DIFFERENCES IN THE TIMING OF FALL MIGRATION OF HAWKS AND FALCONS
Helmut C. Mueller, Nancy S. Mueller, Daniel D. Berger, George Allez, William Robichaud, John L. Kaspar
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Abstract

We trapped more than 23,000 migrating raptors at Cedar Grove, Wisconsin during the autumns of 1953–1996, permitting accurate identification of age and sex. Adults migrated significantly later than juveniles in 8 of 10 species, and males migrated later than females in 7 species. We suggest that it is adaptive for adults and males to remain on breeding territories as long as possible. Adult Peregrine Falcons (Falco peregrinus) migrated before juveniles. There was no age difference in migration of Rough-legged Hawks (Buteo lagopus). Both species breed in the Arctic where the brief breeding season requires that adults leave as soon as possible so adults might then migrate more rapidly than juveniles. We compare our results with those of 16 other studies. Juveniles migrated significantly later than adults in 8 of 13 species at Falsterbo in southern Sweden (Kjellén 1992). Falsterbo is more than 12° latitude (1300 km) north of Cedar Grove and the breeding range of most of the species occurring there extends north of the Arctic Circle, where birds suffer from the same abbreviated breeding seasons as do the Peregrine Falcon and Rough-legged Hawk in North America. Adult females migrated after adult males in the two large species of Accipiter; this may be because the females, not the males, establish and maintain territory in these species.

Helmut C. Mueller, Nancy S. Mueller, Daniel D. Berger, George Allez, William Robichaud, and John L. Kaspar "AGE AND SEX DIFFERENCES IN THE TIMING OF FALL MIGRATION OF HAWKS AND FALCONS," The Wilson Bulletin 112(2), 214-224, (1 June 2000). https://doi.org/10.1676/0043-5643(2000)112[0214:AASDIT]2.0.CO;2
Received: 16 April 1999; Accepted: 1 February 2000; Published: 1 June 2000
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