This bird family comprises swallows and martins. Several genera exhibit hybridization, but only the intergeneric hybrid between Cave Swallow (Petrochelidon fulva) and Barn Swallow (Hirundo rustica) has been studied in greater detail (Martin, 1980; Martin, 1982; Martin & Selander, 1975). Although there are some early reports of swallow hybrids (Mearns, 1902; Trotter, 1878).
Recently, Dunning et al. (2014) described a hybrid between House Martin (Delichon urbicum) and Sand Martin (Riparia riparia), caught in Gibraltar.
A genomic study on two hybrid zones between three subspecies of the Barn Swallow indicated stronger reproductive isolation between rustica and tytleri compared to gutturalis and tytleri (Scordato et al., 2017). This difference in reproductive isolation can be explained by distinct migration strategies in some subspecies pairs, so-called migratory divides (Scordato et al., 2020).
Dunning, J., Hanmer, H. & Christmas, S. E. (2014). Hybridisation between House Martin Delichon urbicum and Sand Martin Riparia riparia: a new observation and review of past occurrences as a case study into hybrid reporting rates. Ringing & Migration 29, 86-89.
Martin, R. F. (1980). Analysis of Hybridization between the Hirundinid Genera Hirundo and Petrochelidon in Texas. Auk 97, 148-159.
Martin, R. F. (1982). Proximate Ecology and Mechanics of Intergeneric Swallow Hybridization (Hirundo-Rustica X Petrochelidon-Fulva). Southwestern Naturalist 27, 218-220.
Martin, R. F. & Selander, R. K. (1975). Morphological and biochemical evidence of hybridization between cave and barn swallows. Condor, 362-364.
Mearns, E. A. (1902). Description of a hybrid between the Barn and Cliff swallows. The Auk 19, 73-74.
Scordato, E.S., Wilkins , M.R., Semenov G., Rubtsov A.S., Kane N.C., Safran, R.J. (2017). Genomic variation across two barn swallow hybrid zones reveals traits associated with divergence in sympatry and allopatry. Molecular Ecology 26, 5676-5691.
Scordato, E. S., Smith, C. C., Semenov, G. A., Liu, Y., Wilkins, M. R., Liang, W., Rubtsov, A., Sundev, G., Koyama, K., Turbek, S. P., Wunder, M. B., Stricker, R. J. & Safran, S. J. (2020). Migratory divides coincide with reproductive barriers across replicated avian hybrid zones above the Tibetan Plateau. Ecology letters, 23(2), 231-241.
Trotter, S. (1878). Description of a hybrid (Hirundo horreori-lunifrons) between two North American swallows. Bull. Nutt. Ornithol. Club 3, 135-136.