Genetic Variation and Parentage in a California Population of Acorn Woodpeckers

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Abstract
Genetic variation was examined in a California population of the highly social acorn woodpecker (M. formicivorus) using starch-gel electrophoresis of 580 blood samples collected between 1975 and 1982. Eighteen genetic loci were resolvable from blood, 2 of which (Mpi and Np) were polymorphic. One additional locus (Est-2) showed variation that was not easily interpreted as an outcome of simple Mendelian inheritance. Average heterozygosity (0.032) was comparable to that of other bird species. Both variable loci showed a slight but not significant deficiency of heterozygotes relative to Hardy-Weinberg expectation. Of 186 nestlings from 62 nests, the genotypes of 4 nestlings (2.2%) from 2 nests (3.2%) were inconsistent with the genotypes of the group breeding males, thus indicating kleptogamy (cuckoldry) in the study population. The low level of genetic variation and the high degree of relatedness between males within groups prevented us from making definitive conclusions concerning the patterns of within-group paternity. Nonetheless, at 1 one-female nest the brood was probably, but not certainly, multiply sired.