Although Golden-winged Warbler and Blue-winged Warbler do not look alike, they are invariably thought of together because they hybridize, producing fertile offspring in two distinct forms: Brewster’s Warbler and the rarer Lawrence’s Warbler. Further crosses produce additional combinations of plumage traits.
Populations of both species have declined over the past several decades, but Golden-winged Warbler numbers have dropped more severely. During the breeding season, both warblers favor early successional habitats, areas that are being lost to development and the reversion of farm and open land to forest.
It has generally been believed that human-caused landscape changes have resulted in more contact, and therefore more hybridization, between the species, and that the more common Blue-winged Warbler would genetically overwhelm the rarer Golden-wing.
A new study, however, is revising not only our understanding of the perceived threat of hybridization but also how to proceed with conservation measures.
Using whole-genome sequencing, rather than a limited number of genetic markers, researchers have found that the two species are remarkably similar: their genomes are 99.97 percent alike. Writing in the journal Current Biology, David P. L. Toews and his colleagues report that only six regions on the genome are markedly different, and four of those are related to feather development or pigmentation, including throat and body color.
The data also indicate that the genetic similarity was likely due to hybridization over many millennia. This is contrary to the notion that it was recent habitat changes that caused the species to come into contact.
Apparently, Golden-winged Warbler and Blue-winged Warbler have been able to maintain their own well-defined plumage traits despite a long history of hybridization. The authors conclude that habitat preservation that benefits both species should be the objective of conservation efforts, rather than focusing on hybridization. – Julie Craves
A version of this article appeared in the December 2016 issue of BirdWatching, which will go on sale at Barnes & Noble and other newsstands in early November. Subscribe.
Read the paper
David P.L. Toews, Scott A. Taylor, Rachel Vallender, Alan Brelsford, Bronwyn G. Butcher, Philipp W. Messer, and Irby J. Lovette (2016). Plumage Genes and Little Else Distinguish the Genomes of Hybridizing Warblers Current Biology, Vol. 26, No. 17 (September 2016), pp. 2313-2318.
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