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| Narrow migration corridors known in diurnal, social migrants such as raptors, storks and geese are thought to be caused by
topographical leading line effects in combination with learning detailed routes across generations. Here, we document
narrow-front migration in a nocturnal, solitary migrant, the common cuckoo Cuculus canorus, using satellite telemetry. We
tracked the migration of adult cuckoos from the breeding grounds in southern Scandinavia (n = 8), to wintering sites in
south-western Central Africa (n = 6) and back to the breeding grounds (n = 3). Migration patterns were very complex; in
addition to the breeding and wintering sites, six different stopover sites were identified during the 16,000 km annual route
that formed a large-scale clockwise loop. Despite this complexity, individuals showed surprisingly similar migration patterns,
with very little variation between routes. We compared observed tracks with simulated routes based on vector orientation
(with and without effects of barriers on orientation and survival). Observed distances between routes were often
significantly smaller than expected if the routes were established on the basis of an innate vector orientation programme.
Average distance between individuals in eastern Sahel after having migrated more than 5,000 km for example, was merely
164 km. This implies that more sophisticated inherent guiding mechanisms, possibly involving elements of intermediate
goal area navigation or more elaborate external cues, are necessary to explain the complex narrow-front migration pattern
observed for the cuckoos in this study. | |
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