Vermivora chrysoptera x cyanoptera
Status: Rare casual spring and fall migrant east.
Documentation: Brewster’s Warbler: photograph, 18 May 2020 Madison Co (Brogie, in gallery); Brewster’s Warbler apparent backcross (F2 Brewster’s and Golden-winged) with Blue-winged Warbler: photograph, 21 May 2020 Sarpy Co (Swanson, in gallery).
Taxonomy: This species and Blue-winged Warbler V. cyanoptera hybridize frequently and produce fertile hybrids; their genomes are 99.97% identical, with plumage genes accounting for the difference (Toews et al 2016). The genetic basis of this hybridization was described by Confer et al (2020) and appears to be a simple Mendelian system whereby the black transocular line and plain throat of cyanoptera are dominant and the black auricular and throat of chrysoptera are recessive. Thus, Brewster’s Warbler is the F1 hybrid between the two parent species and exhibits the black transocular line and pale throat of cyanea that are inherited together, and Lawrence’s Warbler the (F2 or later) backcross form that exhibits the Mendelian recessive gene combination of the black auricular and throat of chrysoptera. Brewster’s Warbler is more common than Lawrence’s Warbler, as predicted by Mendelian inheritance.
Rather startling was a hybrid between a male Chestnut-sided Warbler and a Brewster’s Warbler found in Pennsylvania 7 May 2018, known as the “Burket Triple Hybrid”; it sang a Chestnut-sided Warbler song, as expected since DNA determined the genetic makeup and found that the male parent was a Chestnut-sided (Grove 2019).
Records: There are six Nebraska records. four in spring and two in fall, of Brewster’s Warbler, and none of the recessive form Lawrence’s Warbler. The spring records are rather late in the migration window; hybrids often follow different migration routes and timing than their parent species.
Among the six Brewster’s records, one appears to be an F2 introgressant, likely an F1 hybrid backcrossed with a Blue-winged Warbler, in Sarpy Co 21 May 2020 (Phil Swanson, pers. comm., photo).
18 May 2020 Madison Co (Mark Brogie, pers. comm., photo eBird.org)
19 May 1982 Keya Paha Co (Brogie and Mossman 1983)
21 May 2020 (probable F2 Brewster’s and Golden-winged) Sarpy Co (Phil Swanson, photo)
22 May 2022 Sarpy Co (Phil Swanson photographs)
6 Sep 2007 Fontenelle Forest, Sarpy Co
13 Sep 2008 Oak Grove WMA, Seward Co.
Comments: Genetic studies indicate introgression of cyanoptera haplotypes into chrysoptera phenotypes with no reverse movement (Confer et al 2020), indicating that chrysoptera is being replaced by cyanoptera (Confer et al 2020). The only known phenotypically and genetically pure populations of chrysoptera breed in Manitoba, where numbers are increasing (Confer et al 2020), possibly even to the extent of increasing numbers being reported in Nebraska.
Hover mouse over photos below for captions.
Acknowledgements: Photograph (top) of a Golden-winged x Blue-winged warbler (F2 backcross) 21 May 2020 at Papillion, Sarpy Co by Phil Swanson.
Confer, J.L., P. Hartman, and A. Roth. 2020. Golden-winged Warbler (Vermivora chrysoptera), version 1.0. In Birds of the World (A. F. Poole, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bow.gowwar.01.
Grove, D.S. 2019. The Identification of the Burket Triple Hybrid- a Brewster’s/Chestnut-sided Warbler. Pennsylvania Birds 33: 223-225.
Toews, D.P.L., S.A. Taylor, R. Vallender, A. Brelsford, B.G. Butcher, P.W. Messer, and I.J. Lovette. 2016. Plumage Genes and Little Else Distinguish the Genomes of Hybridizing Warblers. Current Biology 26: 2313-2318.
Silcock, W.R., and J.G. Jorgensen. 2022. Golden-winged x Blue-winged Warbler (hybrid) (Vermivora chrysoptera x cyanoptera). In Birds of Nebraska — Online. www.BirdsofNebraska.org
Updated 30 Jun 2022