Setophaga coronata coronata
Status: Common regular spring and fall migrant statewide. Rare regular winter visitor from North Platte and Platte River Valley counties south and Missouri River Valley in northeast.
Documentation: Specimen: UNSM ZM6857, 20 Apr 1901 Havelock, Lancaster Co.
Taxonomy: The westernmost populations of Myrtle Warbler have been considered separable as hooveri (Curson et al 1994; Dunn and Garrett 1997); this taxon has been described as breeding from Alaska south to British Columbia and wintering from Colorado, Kansas, and Missouri southward (AOU 1957). However, although Pyle (1997) considered differences between coronata and hooveri only clinal and insufficient to warrant subspecific status, Gill et al (2021) retained hooveri along with coronata.
Rapp et al (1958) stated that hooveri (=coronata) occurred in Nebraska.
Intergrades 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. Easterly reports of intergrades are of singles in Lancaster Co 24 Jan 2016 and 25 Apr 2020.
See “Comments” below.
Changes since 2000: Numbers occurring during winter have increased during the past decade based on CBC data (Figure 1). Numbers in Feb in the south especially have increased dramatically beginning in the winter of 2007-2008; prior to that winter there had been only 11 records in all for Feb, but numbers began to increase until the unprecedented count of 16 in Feb 2014-2015.
Figure 1. Number of Yellow-rumped Warblers recorded per party hour during Christmas Bird Counts in Nebraska during the period 1980 to 2016. Points represent reported values and trend line created using locally weighted scatterplot (LOESS) smoothing. Data collected by volunteers and provided by National Audubon Society and the Nebraska Ornithologists Union.
Spring: winter <<<>>> May 23, 25, 25 (south, east); Apr 12, 13, 13 <<<>>> May 20, 20, 20 (north, west)
Earlier dates north and west (Myrtle) are 13 Mar 2011 Custer Co, 30 Mar 2018 Knox Co, 2 Apr 2012 Custer Co, 4 Apr 2010 Custer Co, 6 Apr 2019 Brown Co, and 9 Apr 2012 Custer Co.
Later dates north and west are 3 Jun 2018 Brown Co, and 12 Jun 2010 Garden Co. Jun dates were reported as “Myrtle” warblers.
Later dates south and east are 27 May 2019 Burt Co, 29 May 2017 Sarpy Co, and 31 May 2019 Douglas Co.
Migrants are discernible in the north and west by mid-Apr; peak counts occur in early to mid-May.
There are a few reports Jun-Aug without information on subspecies of these sightings; these are included in Audubon’s Warbler.
- High counts: 755 in Sarpy Co 11 May 1996, 340 at Marsh Wren Community Wetlands, Lancaster Co 3 May 2019, 260 at North Platte NWR, Scotts Bluff Co 3 May 1995, and 255 in Lancaster Co 10 May 1996.
Fall: Sep 12, 12, 14<<<>>> Nov 5, 6, 8 (north, west); Sep 13, 14, 15 <<<>>> winter (south, east),
Earlier dates (reported as Myrtle) in the north and west are 2 Sep 2018 Kimball Co, 6 Sep 2017 Scotts Bluff Co, 8 Sep 2018 Custer Co, and 9 Sep 2017 Scotts Bluff Co. An extraordinary record was of an apparent adult male in Sarpy Co 29 Jul 2021 (eBird, photo). MCl, photo),
A later date in the north and west is 13 Nov 2015 Brown Co.
Migrants become noticeable in mid-Sep and peak migration is in early Oct. Numbers and distribution thereafter begin to decline, with the Sandhills and northern Panhandle vacated in Nov and by Dec most reports are from the south and east.
Reports in Nov-Dec in the north and west are: 6 Dec 1988 Boone Co (Cortelyou 1989), 19 Dec 2018 Wheeler Co, 20 Dec 2018 Garfield Co, 28 Dec 2001 Keya Paha Co, 28 Dec 2010 Loup Co, 22 Dec 2020 Garfield Co, two on 29 Dec 2001 Calamus-Loup CBC, and eight on 30 Dec 1995 Calamus-Loup CBC.
Later reports (Jan-Feb) are discussed under Winter.
- High counts: 129 in Washington-Douglas Cos 13 Oct 1996, 120 in Nance Co 8 Oct 2006, and 120 at Branched Oak Lake SRA, Lancaster Co 6 Oct 2018.
Winter: As noted under Fall (above), by Dec most birds are found in the south. This distribution persists through Feb, but with much reduced numbers that vary markedly from year to year. Prior to winter 2006-2007, there had been only 11 reports for the state in Feb, but beginning in 2007, Feb reports have increased markedly, with nine in the winters 2006-2007 through 2013-2014, followed by an unprecedented 16 reports 2014-2015. There was a similar influx in winter 2015-2016; reports that winter brought the all-time total number of Feb reports to 41, 21 of these in the 2014-2015 and 2015-2016 winters.
Reports are fewest in Jan-Feb, especially north and west of counties along the North Platte, Platte, and Missouri river valleys. There are 18 such reports 2 Jan -27 Feb.
Comments: 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.
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Birds of Nebraska – Online
Updated 13 Oct 2021