Hybridization as an important phenomenon plays a very significant role in evolutionary mechanisms and speciation of Birds. Hybridization is commonly recorded in birds with a high percentage (15%), so hybrid species delimitation is important for studying speciation mechanisms. In this study two mitochondrial genes, ND2 and COI, were applied to delimitate hybrid species in the Palearctic scale. Hybrids are studied in three groups based on their contact zone: sympatric, parapatric, and allopatric hybrids. The results obtained of 1027 bp COI and ND2 genes collected from 250 separated individuals showed a remarkable operation of COI gene in separation of parapatric hybrids than ND2 one. Therefore, COI gene as a useful marker for species discovery also can be used with higher performance to identify hybridizing parapatric species pairs. Furthermore, this study showed a higher molecular divergence in sympatric hybrid species pairs than parapatric, and allopatric ones. Thus the subject confirms the sympatric speciation hypothesis in avian species.

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