Great Spotted and Syrian Woodpeckers (Dendrocopos major and D. syriacus) are known to hybridize in nature; however, the extent of this phenomenon is not known due to difficulties in hybrid detection based on plumage analyses. Here, we tested five markers (one mitochondrial and four nuclear) and a set of six microsatellite loci for the identification of these two Woodpeckers and their hybrids. Sequencing of DNA from 26 individuals of both Woodpeckers from different parts of their ranges: one allopatric (D. major; Norway) and two sympatric (Poland and Bulgaria) showed that both species can be clearly separated based on all sequence markers. The highest number of fixed nucleotide sites were found in the mtDNA control region and intron 5 of the transforming growth factor. Analyses of microsatellite data distinguished the two species, but all loci showed a large number of common alleles and their utility in identifying hybrids is therefore doubtful. According to the DNA sequence analyses, 2 out of 18 specimens within the sympatric range in Poland were identified as possible hybrids, most probably paternal backcrosses. Moreover, both hybrids are from synantropic populations (settled in cities), whereas none of the D. major sampled in forests and in its allopatric range (Norway) showed signs of an intermixed genotype. Further research on hybridization and introgression in woodpeckers is undoubtedly needed and could be useful for understanding ecological and ethological interactions among these species, particularly for D. syriacus, which is relatively rare in Europe.

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Polen wurden bezüglich des Vorkommens von gemischten Paaren und Hybriden untersucht. Es wurde geschätzt, dass 5.3% der Paare gemischt waren und diese interspezifischen Paare hauptsächlich aus SW-bzw. Hybridweibchen und GW-Männchen bestanden. Insgesamt wurden 3.6% der beobachteten Individuen und 6.9% der toten Vögel als Hybriden identifiziert. Das Geschlechterverhältnis der Hybriden war ausgeglichen. Diese Daten deuten darauf hin, dass Hybridisierung zwischen diesen beiden Spechtarten ein unterschätztes Phänomen sein könnte, das wichtige Konsequenzen für ökologische Studien und den Schutz des seltenen Blutspechts hat.

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Recent high-throughput genotyping technologies allow for comprehensive genomic analyses on an unprecedented scale. However the advantages of the most commonly used tools are strongly limited in non-model organisms, including wild birds. In this study we attempt to test the utility of genotyping by sequencing (GBS) without relying on the reference genome sequence in selected pairs of sibling bird species that are known to hybridize (Syrian and Great Spotted Woodpeckers). We found that GBS is able to produce a satisfying number of polymorphisms and can be successfully applied to the population genetics of these species. The results also suggest that urban populations of these woodpeckers, especially phenotypic Syrian Woodpeckers, consist of individuals that harbor genotypes assigned to Great Spotted Woodpeckers, which suggests intensive hybridization and introgression.