REGIONAL VARIATION IN THE DISTRACTION DISPLAYS OF THE OYSTER‐CATCHER.

Summary. The Oyster‐catcher Haematopus astralegus populations of western Europe (Holland, South Britain, Fair Isle, Unst and Faeroe Islands) differ very little morphologicallv, but show interesting variations in their distraction displays. These displays, comprising (1) aggressive flight, (2) a furtive run, (3) false‐brooding, (4) pseudo‐sleeping, and (5) lure display, are described, with comments on their regional importance. Aggressive flight, false‐brooding and lure display are more strongly developed in Faeroe than elsewhere. At Fair Isle (and to a less extent at Unst) displacement “ butterfly‐flight” replaces lure display. It is shown that the lure display has evolved as a terrestrial modification of displacement “ butterfly‐flight”, which has proceeded furthest in the Faeroe population, hardly at all in the more southerly populations, and to an intermediate degree among the birds of Unst. The Oyster‐catcher's extension to the Faeroe Islands—probably from the British area, in Comparatively recent times—involved colonization of an atypical moorland habitat. The distraction displays appear to have been perfected in the absence of terrestrial predators other than men and dogs, which have been present for about 1000 years. The remarkable development of these display patterns is probably due to hereditan differences, affecting ethological attributes, which have arisen between the Faeroe and the more southerly populations. It is suggested that their evolution has been stimulated by the psychological effect of frequent disturbance of the brooding urge by man, during the attempt to colonize a new and unsympathetic environment.