Testing the effect of migratory restlessness on the occurrence of vagrant continental passerines in Japan

摘要

Many vagrant passerines from the Western Palearctic have been documented in Japan. In the present study, I tested the following two hypotheses: (1) the vagrancy of continental passerines migrating to Japan is affected by migratory distance and migratory direction, rather than distance from the normal distributional range; and (2) the vagrancy of continental passerines migrating to Japan is related to migratory restlessness. Data on vagrants were collected from various sources, and the effects of migratory distance, distance from the normal distributional range, migratory restlessness, migratory direction, and normal distribution size were examined. The results revealed significant positive effects of migratory distance and migratory restlessness, with these effects being significant even when the effects of other variables were controlled. The normal distribution size had a marginally significant positive effect, but none of the remaining variables predicted the occurrence of vagrants. The vicinity of the normal distributional range of continental passerines was not a predictor of vagrancy. These findings indicate that the endogenous migratory program of individuals is responsible for the occurrence of vagrants in Japan, and that sufficiently restless birds may reach the Far East.