Predictable outcomes of warbler hybridization: Synthesis and an exceptional Yellow × Black-throated Blue Warbler (Setophaga petechia × S. caerulescens) pairing

Abstract

Hybridization can have profound effects on biological diversity. However, predictable inheritance of plumage traits remains poorly understood, especially for rare hybrids. We reviewed the literature and compiled a comprehensive list of hybrids from the New World 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 describe an unusual hybrid from the University of New Mexico in Albuquerque, New Mexico, southwestern USA. We identified evidence of hybridization in 44 of 47 (93%) North American parulid species, with the highest number of hybrids found in the genus Setophaga. Plumage patterns between hybrid offspring and parental forms in our 2 focal traits were predictable, supporting the identification of our hybrid as a Yellow × Black-throated Blue Warbler (S. petechia × 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 phenotypes of rare hybrid warblers likely have some degree of predictability.