DNA Identification of a Putative Hybrid Azure Tit × Blue Tit

Hybridization is an important factor in bird evolution. Distinguishing between hybrids and phenotypically aberrant individuals of one of the parental species can be challenging. Here, we use DNA sequencing of loci on chromosomes 2 and Z and the mitochondrial DNA to establish the status of a putative hybrid Azure Tit Cyanistes cyanus X Blue Tit Cyanistes caeruleus caught in Belgium in 2021. The genotype at each of these loci was a perfect match to Blue Tit. We therefore conclude that the bird was a genetically pure Blue Tit, despite its plumage being intermediate between Azure Tit and Blue Tit. We suggest records of Pleske's Tit lacking DNA information should be treated with caution.