Common Buzzard (Buteo buteo): A raptor with hyperpolymorphic plumage morphs, but low allozyme heterozygosity

The analysis of 25 allozyme loci in up to 469 Common Buzzards (B. b, buteo) from five locations in Germany revealed allelic polymorphism at twelve loc i, but a prevalence of rare alleles resulted in a very low heterozygosity o f H-0 = 0.0057. This rather low level of genetic variation characterizes a most abundant raptor species with highly polymorphic plumage pigmentation. The results of monitoring 571 buzzard breeding pairs from the Hakel forest (Sachsen-Anhalt) over 27 years indicate that neither the among-pair fertili ty variance, which slightly increased the genetically effective population size against the numerical size, nor the yearwise fluctuation of the breede r numbers, nor other population ecological characters were likely to erode the genetic variation of the numerically large buzzard population. One or r epeated phyletic or historical bottle-necks are postulated to have diminish ed the allozyme variability, and at the same time to have created new genet ic variance of the pigment-coding genes from non-additive components of gen etic variance. Thus, the plumage colour diversity of the Common Buzzard cou ld be a direct result of diminished single-locus genetic variation.