Comparing captive and wild owl hybrids reveals divergence in size of parental species, but not in iris coloration

Avian hybridization has been predominantly studied in natural contexts, such as hybrid zones or the identification of hybrid individuals. However, captive settings offer a complementary framework for understanding the ecological and evolutionary mechanisms underlying hybridization. Artificial conditions might relax premating isolation barriers that typically prevent interspecific breeding in the wild, although certain mate recognition mechanisms could remain effective in captivity. Here, I present a comparative analysis of wild and captive hybrids in owls (order Strigiformes; families Tytonidae and Strigidae) to test two predictions: (1) captivity facilitates hybridization between morphologically more divergent species than observed under natural conditions, and (2) certain premating isolation mechanisms are still effective in captivity, with a focus on iris coloration as a visual cue in species recognition. In total, I compiled an overview of 26 reported cases of owl hybridization. Of these cases, 11 (42%) were supported by reliable documentation, involving 19 species (8% of 244 assessed species). Seven additional cases (27%) remain provisional, and eight (31%) were deemed unreliable. Comparative analyses of morphological traits indicated that captive hybrid pairs showed a broader range of interspecific differences in body mass, tarsus length, and wing length than natural hybrid pairs. No consistent differences were found between captive and natural hybrid pairs in terms of iris coloration, activity pattern, or trophic niche. Overall, hybridization in owls appears rare. The tendency for captive hybrids to involve morphologically divergent species suggests that artificial conditions relax certain constraints on interbreeding. However, the similarity in iris coloration among most hybridizing species supports a potential role for this trait in premating isolation. Future studies integrating genomic data, experimental approaches, and broader comparative datasets will be needed to clarify the impact of captivity on reproductive barriers.