Abstract
Being an obligate parasite, juvenile common cuckoos Cuculus canorus are thought to reach their African wintering grounds from Palearctic breeding grounds without guidance from experienced conspecifics but this has not been documented. We used satellite tracking to study naïve migrating common cuckoos. Juvenile cuckoos left breeding sites in Finland moving slowly and less consistently directed than adult cuckoos. Migration of the juveniles (N = 5) was initiated later than adults (N = 20), was directed toward the southwest–significantly different from the initial southeast direction of adults–and included strikingly long Baltic Sea crossings (N = 3). After initial migration of juvenile cuckoos toward Poland, the migration direction changed and proceeded due south, directly toward the winter grounds, as revealed by a single tag transmitting until arrival in Northwest Angola where northern adult cuckoos regularly winter. Compared to adults, the juvenile travelled straighter and faster, potentially correcting for wind drift along the route. That both migration route and timing differed from adults indicates that juvenile cuckoos are able to reach proper wintering grounds independently, guided only by their innate migration programme.
Highlights
Evidence about actual migration in solitary, nocturnal migrant birds is scarce and even mapping the spatiotemporal migration routes of individuals has only been accomplished for a few species [1]
We focus our analyses on spatiotemporal overlap in migration routes with adult cuckoos from nearby breeding grounds in North Scandinavia
The North-Central European stopover used by the juvenile birds was in the same area as that used by southern adults, which was 600 km west of the area used by northern adults
Summary
Evidence about actual migration in solitary, nocturnal migrant birds is scarce and even mapping the spatiotemporal migration routes of individuals has only been accomplished for a few species [1]. Juvenile long-distance migrants of most nocturnal land-birds presumably migrate solitarily and without guidance from adults [2,3,4]. Documenting whether juvenile migrants travel independently of adults and whether they follow the same routes as adults has not been possible for smaller species because the necessary technology was unavailable [5]. Lack of suitable technology has hindered the study of how the inherited spatiotemporal guiding programme unfolds in free-flying individuals, for instance in route learning [6] and dealing with wind drift [7].
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