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| We tested whether routes of raptors migrating over areas with homogeneous topography follow constant
geomagnetic courses more or less closely than constant geographical courses.We analysed the routes taken
over land of 45 individual raptors tracked by satellite-based radiotelemetry: 25 peregrine falcons, Falco peregrinus,
on autumn migration between North and South America, and seven honey buzzards, Pernis apivorus,
and 13 ospreys, Pandion haliaetus, on autumn migration between Europe and Africa. Overall, migration
directions showed a better agreement with constant geographical than constant geomagnetic courses.
Tracks deviated significantly from constant geomagnetic courses, but were not significantly different
from geographical courses. After we removed movements directed far from the mean direction, which
may not be migratory movements, migration directions still showed a better agreement with constant geographical
than constant geomagnetic courses, but the directions of honey buzzards and ospreys were not
significantly different from constant geomagnetic courses either. That migration routes of raptors followed
by satellite telemetry are in closer accordance with constant geographical compass courses than with constant
geomagnetic compass courses may indicate that geographical (e.g. based on celestial cues) rather
than magnetic compass mechanisms are of dominating importance for the birds’ long-distance
orientation. | |
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