The Incidence of Vagrant Landbirds on Nova Scotian Islands

Many vagrant landbirds have occurred on Brier, Sable, and Seal islands, Nova Scotia and have produced first records for Nova Scotia or Canada.In counts made on these islands for more than a decade, individuals of western species were relatively more common than in similar counts on islands off northeastern Florida in spring and North Carolina in fall.Western vagrants were more frequent, but much less diverse, on the Florida islands in fall.Recent checklists substantiate the conclusion that vagrant species from remote ranges are more diverse on the Nova ScotJan islands than in other localities in eastern North America.The diversity and high incidence of vagrants may be related partly to the convergence of continental windstreams on Nova Scotia during migration seasons.Regional species, however, evidently avoid Sable Island, which is farthest offshore, whereas vagrants from remote ranges are relatively more common there than on the other two islands.This suggests that navigational error by "lost" vagrants is paramount.Weather patterns are examined in association with the earliest vagrants of each season, as these vagrants may have come most rapidly and directly.Southern vagrants may fly past their normal ranges in spring, unassisted by winds.Western species in spring are probably not generally deflected from their normal routes by winds.Western Dendroica spp. in spring in the east may come because of mirror-image disorientation.Southern vagrants are proportionately as common in fall as in spring, and individuals may or may not be wind-assisted in their reverse migrations.Western vagrants are relatively more common in fall than in spring.Some may come directly down-wind on fall westerlies, but their relatively high incidence in Nova Scotia may result from their being swept up the east coast by prevailing southwesterlies.Turn-of-the-century records from Sable Island suggest that vagrancy may have increased among species that have expanded their populations or ranges, especially those of disturbed habitats.Received 16 May 1978, accepted 5 July 1980.LIKE some other places at the edges of continents, certain islands off Nova Scotia are visited by a remarkable variety of birds.Here I argue that the incidence of vagrants among these birds is higher than elsewhere in eastern North America and offer some explanations.The analysis is confined to landbirds, as seabirds and waterfowl need not use the islands, and the relative abundances of herons, shorebirds, and marsh birds may reflect available habitats.Three islands off Nova Scotia (Fig. 1) are the main sources of information.Brier Island is virtually connected to the mainland through another island and a long peninsula.Seal Island is about 25 km off the south end of the province, and Sable Island is about 150 km from the mainland.Sable Island has long been known for its birds.Although there are casual earlier accounts, Dwight's (1895) visit in 1894 stimulated the interest in birds of the children of R. J. Bouteillier, Superintendent of the Life Saving Establishment on the island.One result is 219 bird skins, some unusual and hitherto undocumented, now in the Dwight collections at the American Museum of Natural History, New York and the Science Museum, Springfield, Massachusetts.Between 1900 and 1908, James and Richard Bouteillier also sent out lists of birds they recorded.Some were published (Boutelier 1901; Bouteiller 1905, 1906, 1908; Bouteiler 1908; their name is persistenfly misspelt in these papers and in references to them, but their holographic version is Bouteillier).Their unpublished lists and some of their published ones are on file at the Nova Scotia Museum of Science, Halifax.There is also on file an 243The Auk 98: 243-257.

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