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Photos of a rare warbler hybrid, Yellow Warbler x Black-throated Blue Warbler (Setophaga petechia x Setophaga caerulescens)

Cite this dataset

Gyllenhaal, Ethan (2021). Photos of a rare warbler hybrid, Yellow Warbler x Black-throated Blue Warbler (Setophaga petechia x Setophaga caerulescens) [Dataset]. Dryad.


Hybridization can have profound effects on biological diversity; however, predictable inheritance of plumage traits remains poorly understood, especially for rare hybrids that are infrequently documented. We reviewed the literature and compiled a comprehensive list of hybrids from the wood warbler family Parulidae, a diverse radiation of songbirds with divergent plumage traits. We used our compilation to analyze modes of inheritance in wing bar patterns and carotenoid coloration. Finally, we described an unusual hybrid from the University of New Mexico in Albuquerque, New Mexico. We identified evidence of hybridization in 44 of 47 (93%) North American parulid species, with highest rates of hybridization in the genus Setophaga. We found predictable inheritance of plumage patterns between hybrid offspring and parental forms in our two focal traits, which supports the identification of our hybrid as a Yellow Warbler x Black-throated Blue Warbler (S. petechia x S. caerulescens). We based our identification on the extent and pattern of white in the tail, a prominent white wing flag, and our ability to confidently rule out all other alternative parentals. Our results suggest that some hybrid pairings can be confidently identified from phenotype alone, and that phenotypes of rare hybrid warblers likely have some degree of predictability.


Photos were taken by Michael J. Andersen and Kristen M. Oliver during an extended observation session of this exceptional hybrid warbler pairing, which enabled us to use prior knowledge of hybrid phenotypes to identify this unlikely hybrid.

Usage notes

You are free to use photos posted here, but we would appreciate if you credit the photographer of a given image if used (see README and associated zip directories) and cite the article if applicable:

Williamson, J. L., Gyllenhaal, E. F., Oliver, K. D., Brady, S. S., Johnson, A. B., Michelsohn, M. J., & Andersen, M. J. (n.d.). Predictable outcomes of warbler hybridization: Synthesis and an exceptional Yellow × Black-throated Blue Warbler (Setophaga petechia × S. caerulescens) pairing. The Wilson Journal of Ornithology.