Black-headed Bunting Emberiza melanocephala and Red-headed Bunting Emberiza bruniceps are closely related passerine species that were reported to meet in a hybrid zone southeast of the Caspian Sea, Iran, over 70 years ago. In this study, we revisited the hybrid zone in the northern parts of Iran to compare its present extension and position with previous reports and to determine the relative importance of intrinsic and extrinsic factors in defining range limits of these bunting species in the contact zone. Species Distribution Models (SDMs) were constructed to characterize the factors affecting the current location of the zone. Our results show that the hybrid zone has expanded westwards approximately 170 km in recent decades and that the Black-headed Bunting is being replaced by the Red-headed Bunting in a westward movement. The Blackheaded Bunting has retreated a little from its eastern range in north Iran in recent decades. The hybrid zone has expanded westward rather than shifted. Model outputs show that climatically suitable habitats for both species extend far beyond the hybrid zone. This mismatch between the potential and realized distribution for the two species suggests that intrinsic factors play a major role in shaping range limits of these hybridizing bunting species.
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