Figure 20.3 Orientation directions of Blackcaps Sylvia atricapilla from two populations breeding east and west of a migratory divide in Europe, and from hybrids between these two populations. Within the inner circle, triangles indicate the parental population from southwest Germany (filled) and eastern Austria (open), while in the outer circle, dots show first-generation offspring of mixed pairs bred in aviaries. Arrowheads indicate group mean directions. The hybrids took mean directions intermediate between the two parental forms. Note the seasonal shift in direction shown in November by the southeastward migrating parents and the intermediate mean orientation of the hybrid offspring. From Helbig (1991b, 1996).
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