Title: A Long-Distance Avian Migrant Compensates for Longitudinal Displacement during Spring Migration
Abstract: In order to perform true bicoordinate navigation, migratory birds need to be able to determine geographic latitude and longitude. The determination of latitude is relatively easy from either stellar or magnetic cues [1Able K.P. Mechanisms of orientation, navigation and homing.in: Gauthreaux S. Animal Migration, Orientation and Navigation. Academic Press, New York1980: 283-373Crossref Google Scholar, 2Wiltschko R. Wiltschko W. Magnetic Orientation in Animals. Springer-Verlag, Berlin1995Crossref Google Scholar, 3Gould J.L. Sensory basis of navigation.Curr. Biol. 1998; 8: R731-R738Abstract Full Text Full Text PDF PubMed Google Scholar], but the determination of longitude seems challenging [4Mouritsen H. Larsen O.N. Migrating songbirds tested in computer-controlled Emlen funnels use stellar cues for a time-independent compass.J. Exp. Biol. 2001; 204: 3855-3865PubMed Google Scholar, 5Mouritsen H. Spatiotemporal orientation strategies of long-distance migrants.in: Berthold P. Gwinner E. Sonnenschein E. Avian Migration. Springer, Berlin, Heidelberg, New York2003: 493-513Crossref Google Scholar]. It has therefore been suggested that migrating birds are unable to perform bicoordinate navigation and that they probably only determine latitude during their return migration [5Mouritsen H. Spatiotemporal orientation strategies of long-distance migrants.in: Berthold P. Gwinner E. Sonnenschein E. Avian Migration. Springer, Berlin, Heidelberg, New York2003: 493-513Crossref Google Scholar]. However, proper testing of this hypothesis requires displacement experiments with night-migratory songbirds in spring that have not been performed. We therefore displaced migrating Eurasian reed warblers (Acrocephalus scirpaceus) during spring migration about 1000 km toward the east and found that they were correcting for displacements by shifting their orientation from the northeast at the capture site to the northwest after the displacement. This new direction would lead them to their expected breeding areas. Our results suggest that Eurasian reed warblers are able to determine longitude and perform bicoordinate navigation. This finding is surprising and presents a new intellectual challenge to bird migration researchers, namely, which cues enable birds to determine their east-west position.