A circannual perspective on daily and total flight distances in a long-distance migratory raptor, the Montagu’s harrier, Circus pygargus.
Résumé
Long-distance migrants are particularly recognized for the distances covered on migration, yet little is known about the distances they cover during the rest of the year. GPS-tracks of 29 Montagu’s harriers from breeding areas in France, The Netherlands and Denmark showed that harriers fly between 35 653 and 88 049 km yr21, of which on average only 28.5% is on migration. Mean daily distances during migration were 296 km d21 in autumn and 252 km d21 in spring. Surprisingly, males’ daily distances during breeding (217 km d21) were close to those during migration, whereas breeding females moved significantly less (101 km d21) than males. In terms of flight distance, the breeding season seemed nearly as demanding as migration periods for males. During the six winter months, both sexes moved less (114 and 128 km d21 for females and males, respectively) than during migration. Harriers therefore covered shorter daily distances during winter which might allow birds to compensate for the more demanding phases of migration and breeding.