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Abstract

Directional Preferences of Autumnal Migratory Restlessness in Two Populations of Blackcaps (Sylvia atricapilla) with Different Migratory Directions

The directional preferences in the orientation behavior of blackcaps, Sylvia atricapilla, were investigated. Two populations on different sides of the migratory divide were studied; one which flies in a SE direction in autumn and one which flies in a SW direction. The populations were from Lake Constance in the F.R.G. and Lake Neusiedl in Austria. Directional preference during fall migratory restlessness was determined by using Emlen funnels. The birds were hand-raised from the nestling phase on under identical conditions.

The results demonstrated significant differences between the populations in the autumnal directional preferences. For SW migrants it was 240.7° and for SE migrants 185.0°. One can conclude from these results that there are population-specific differences in the innate directional preferences of fall migratory restlessness.

A number of possibilities are discussed as causes for the extreme westward orientation of the birds from Lake Constance:

  • 1
    The WSW orientation of the Alps could be genetically programmed into the pattern of migration.
  • 2
    It could have been the result of a compensation for the transport from Lake Constance to Lake Neusiedl and therefore explained by goal area navigation.
  • 3
    Recently, there have been many reports of German blackcaps wintering in Holland, England and Ireland. It is possible that a number of the experimental birds had already chosen this direction and with their WNW preference, the overall preference is shifted westward.