Vagrancy theories: are autumn vagrants really reverse migrants?

Published on 01 September 2003 in Main articles

ABSTRACT Reverse migration is a popular concept, often used to explain the occurrence of autumn vagrants.The term `reverse migration shadow’ has been used to identify regions in which autumn vagrancy of a given species may occur, and to predict potential future vagrants to Britain. In this paper, we evaluate this theory and, by analysing vagrancy patterns, demonstrate that autumn vagrancy is not limited to the `shadow’ of a 180° route-reversal. Although the vast majority of individuals follow a traditional route to winter quarters, vagrancy during autumn migration occurs in all directions, and we contend that it is the pattern of observer coverage which determines the number of vagrants discovered.The occurrence patterns of some vagrants reaching Britain can be explained using the idea of long-range dispersal. We suggest that some comparatively regular vagrants reaching Britain are, in fact, performing annual migrations to presently undiscovered wintering grounds in western Europe or West Africa.In the river valleys and on the low, densely forested hills, Leopards Panthera pardus stalk through the undergrowth, and the beautiful Asian Paradise Flycatchers Terpsiphone paradisi flit restlessly among the branches… Higher up the mountains, the bright southern birds are left behind in an enchanting sea of sounds, scents and colours. In their place stands the more solemn but equally beautiful world of the coniferous taiga, where the cool silence is perhaps broken only by the simple but sweet song of a Pallas’s Warbler Phylloscopus proregulus. (Algirdas Knystautas 1987)allas’s Leaf Warbler Phylloscopus proregulus is a bird of the vast boreal

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