Variability in morphological features is one mechanism by which recognition of individuals or kin, crucial to many social interactions, can occur. Patches in the remiges of magpie wings (white patches with black tips) contain information regarding the bearer's age and sex. Juvenile wing patches of both Black-billed Pica pica hudsonia and Yellow-billed Magpies Pica nuttalli contain between 10 to 12 feathers with variable lengths of white. Our investigations examine the relationship between wing patch morphology and relatedness. We measured the black tips on the primaries of one wing on 29 fledglings from seven nests. We derived a discriminant function based on the length of black on three inner primaries that successfully assigned 75 % of the birds to their natal nests (random assignment = 14% correct). We also compared the total length of black tips in the wing patches of young from 33 nests. We found less variation in the patch size within than between nests (log transformed ANOVA F = 8.339, p < 0.001; Kruskal-Wallis H = 113.6, p < 0.001). These results suggest that familial resemblance is encoded in juvenal magpie wing patches. Family recognition may be important both to the parents, who provide protection and food for their young, as well as between siblings, who apparently know each other.
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