Setophaga coronata x SETOPHAGA Auduboni
Status: Uncommon spring and fall migrant west and central, rare east. Rare casual winter visitor east.
Taxonomy: The subspecies coronata and auduboni were at one time considered separate species, Myrtle and Audubon’s Warblers respectively, but since 1983 have been treated as conspecifics due to the presence of hybrid zones from northwest British Columbia to southwest Alberta (Barrowclough 1980, AOU 1983). Curson et al (1994) suggested, however, that a more appropriate treatment is to consider the two taxa as two of four allospecies within the superspecies [S.] coronata, the others nigrifrons (Black-fronted Warbler) of the southwest United States and goldmani (Goldman’s Warbler) of southern Mexico. Analysis of a narrow hybrid zone in Alberta supports this treatment; although genetic distance between coronata and auduboni is slight, the hybrid zone has remained narrow and stable, suggesting assortative mating (Hunt and Flaspohler 2020). Indeed, Gill et al (2021) separate coronata and auduboni as full species, along with nigrifrons and goldmani, although nigrifrons is now considered a subspecies of Audubon’s Warbler.
Genetic evidence suggests that, rather than Myrtle and Audubon’s arising as a result of allopatric isolation, Audubon’s is a rare avian example of a taxon of hybrid origin. Its genome contains alleles derived from both presumed parental taxa, migratory Myrtle and non-migratory Black-fronted (Brelsford et al 2011); isotope studies show that Audubon’s possesses Myrtle rather than Black-fronted genes at an allele associated with migration (Toews et al 2014), resulting in the migratory capability of Audubon’s Warbler.
Hybrids between Audubon’s and Myrtle Warbler are fairly common. An often-reported form resembles Audubon’s Warbler, but the yellow throat is outlined in white. A male collected 20 Apr 1920, UNSM ZM6849, in Lancaster Co has yellowish feathering on a white throat and limited whitish wing bars. One at Lake Ogallala, Keith Co 15 Feb 2015 had the facial and throat pattern of Audubon’s Warbler, but its calls resembled those of Myrtle Warbler. In 2020, there were 14 reports in the west and west-central of “Myrtle X Audubon’s” Yellow-rumped Warblers 19 Sep-16 Nov with varying amounts of white on the throat and various combinations of throat color and presence or absence of a white supercilium. In 2022, there were five such reports 25 Apr-8 May and 12 for 16 Sep-18 Oct.
Almost all Nebraska records of this hybrid are in spring and fall, as might be expected since the hybrid zone between coronata and auduboni is in parts of British Columbia and Alberta.
Spring: Apr 23, 23, 25 <<<>>> May 11, 11, 13
Later dates are 15 May 2020 Oliver Reservoir, Lincoln Co, 22 May 2021 Oliver Reservoir, and 23 May 2010 Crescent Lake NWR, Garden Co.
Of the eight records for the east, seven are during 26-30 Apr, and one in Oct., whereas in the central, of the 20 records, five are in spring 23 Apr-8 May, and 15 in fall 26 Sep-19 Nov.
Statewide, there are 30 records for spring and 40 for fall, plus two winter records.
High Counts: 5 at Oliver Reservoir, Kimball Co 13 May 2023.
Fall: Sep 21, 22, 22 <<<>>> Oct 17, 17, 18
Later dates are 21 Oct 2020 Dawes Co, 26 Oct 2020 Kimball Co, 29 Oct-19 Nov 2021 (1-2) Sutherland Reservoir, Lincoln Co, and 16 Nov 2020 Dundy Co.
Winter: There are three records, two in the east:
22 Dec 2018 Lancaster Co (eBird.org)
24 Jan 2016 Lancaster Co (eBird.org)
15 Feb 2015 Lake Ogallala, Keith Co.
Images
Literature Cited
American Ornithologists’ Union [AOU]. 1983. The AOU Check-list of North American birds, 6th ed. Allen Press, Lawrence, Kansas, USA.
Barrowclough, G.F. 1980. Genetic and phenotypic differentiation in a Wood Warbler (Genus Dendroica) hybrid zone. Auk 97 :655-668.
Brelsford, A., B. Mila, and D.E. Irwin. 2011. Hybrid origin of Audubon’s Warbler. Molecular Ecology 20: 2380–2389.
Curson, J., D. Quinn, and D. Beadle. 1994. Warblers of the Americas. Houghton Mifflin Company, Boston, Massachusetts, USA.
Gill, F., D. Donsker, and P. Rasmussen (Eds). 2021. IOC World Bird List (v 11.2). Doi 10.14344/IOC.ML.11.2. http://www.worldbirdnames.org/.
Toews, D.P.L., A. Brelsford, and D.E. Irwin. 2014. Isotopic variation across the Audubon’s–myrtle warbler hybrid zone. Journal of Evolutionary Biology 27: 1179–1191.
Recommended Citation
Silcock, W.R., and J.G. Jorgensen. 2024. Myrtle x Aubudon’s Warbler (Setophaga coronata x auduboni). In Birds of Nebraska — Online. www.BirdsofNebraska.org
Birds of Nebraska – Online
Updated 5 Jan 2024