Do birds that become lost on migration ever get back on course or find their way home? Not always says Mike Toms.
Individuals lost while on migration are known as vagrants - and vagrancy is one of the factors that makes birdwatching so interesting.
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Yet the thrill of seeing an individual far from where it should be is often tinged with the sad assumption that it is unlikely to get back on course.
However, many birds that have not strayed far from their original path do find their way back to their usual migration routes. For example, those that have been swept across the North Sea by strong easterly winds during their autumn migration usually manage to modify their route accordingly and get back on track.
Research into the mechanisms by which birds navigate, including a famous experiment in which migrating starlings were deliberately displaced from the Netherlands to Switzerland, has highlighted the conditions under which birds can compensate for their vagrancy.
It seems that first-year birds struggle to adjust and simply continue on their original compass bearing. Older birds, however, will amend their route, seemingly using experience to redirect their onward journey.
Birds that have been displaced by much larger distances leg North American birds blown to Europe by storms) face a much tougher challenge. The evidence suggests that these individuals never find their way home.
