Lawrence's Warbler

A scrubby successional habitat in Medina County, on a fine morning. I visited this site on June 11, 2025, to seek a very special bird. Letha House Park is part of the Medina County Park District, and it contains a diverse mixture of habitats: old fields, young forest, wetlands, a pond, and most germane to this story, young shrubby thickets.

On April 29, the rare hybrid Lawrence's Warbler was discovered in the very patch in my photo above. The white flowers, by the way, are Smooth Beardtongue (Penstemon digitalis). It wasn't that herb that lured the Lawrence's Warbler, though, it was the mixture of young pole-sized trees and associated brushy growth.

While I can't recall now who found the bird, I think it was Debbie Parker, and/or Joe Wojnarowski. Both reported the bird to eBird on April 29, the first date it was reported. I watched the reports with great interest as time went on but was too busy with various activities to make the trip, although the Lawrence's was reported daily throughout May.

As always, click the photo to enlarge

Finally! June 11 arrives and so does a free and clear day. I hit the road long before sunup and arrived on a beautifully sunny morning with excellent light for photography. I don't think I had even fully exited the vehicle before I heard the hybrid's distinctive buzzy song and soon found the singer in a young sycamore.

The Lawrence's Warbler is a hybrid between the Blue-winged Warbler (Vermivora cyanoptera) and Golden-winged Warbler (V. chrysoptera). The former parent species remains fairly common where appropriate habitat remains, while the latter parent has declined alarmingly across much of its range.

If one uses the Biological Species Concept as a framework for deciding what constitutes a species (as many scientists do), they will be confronted with this tenet: The biological species concept defines a species as members of populations that actually or potentially interbreed in nature, not according to similarity of appearance. Although appearance is helpful in identifying species, it does not define species.

Differing visual appearances sometimes have little to do with speciation. Take the Eastern and Western meadowlarks (Sturnella magna and S. neglecta). Most birders would struggle mightily telling those two apart visually. But their songs are different as night and day and with the slightest experience, anyone would instantly recognize them. Those songs probably serve as a primary barrier in limiting contact between the two. There is a narrow band of overlapping range, but even there, hybridization is apparently very rare.

Yet the Blue-winged and Golden-winged warblers look completely different. Anyone would think they were different species with just a glance. And indeed, they are and always have been treated as separate species. But should they?

The Medina County Lawrence's Warbler strikes a pose. I would argue that it is more beautiful than either parent species, or its fellow hybrid the Brewster's Warbler.

About 190 years ago, the legendary frontier ornithologist John James Audubon wrote a letter to his mentor and confidant, John Bachman, in which he speculated that Blue-winged and Golden-winged warblers were the same species. Audubon, a keen observer if there ever was one, no doubt noted mixed pairings and similarities in songs and structure.

It wasn't until 1886 that the inaugural American Ornithologists' Union Checklist of North American Birds appeared, over 50 years after Audubon's prescient Blue-winged/Golden-winged observations noted in his September 15, 1835, missive to Bachman. This checklist is widely considered the standard for North American bird nomenclature. Numerous editions and supplements to the checklist have been published since, but from the first to the current checklist, Blue-winged and Golden-winged warblers have been maintained as separate species. I would note that the scientific name of the Blue-winged changed three times over the checklist's history, and the Golden-winged's twice. English names tend to be far more stable than the ever-shifting landscape of scientific nomenclature.

In the mid-2010's, scientists with the Cornell Lab of Ornithology undertook an intensive study of the genetics of the Blue-winged and Golden-winged warblers. The results weren't very surprising, in my estimation, but provide solid evidence of their genetic similarity. In short, the two "species" are 99.7% genetically identical. Only six regions (0.3%) of the genome reflect distinct differences. This is basically akin to the differences between a human with red hair, and one with blond hair. The Cornall researchers note that the genetic differences between the two groups of Swainson's Thrush (each comprised of three subspecies) are greater than the differences between the two warblers.

When they come into contact, Blue-winged and Golden-winged pairings result in two distinct - and fertile hybrids: the Brewster's Warbler, and Lawrence's Warbler. Brewster's manifests the dominant traits such as the yellow throat and white underparts, while the Lawrence's Warbler manifests recessive traits such as the black throat and yellow underparts. Brewster's hybrids occur more frequently, hence my interest in seeing and photographing the protagonist of this blog post (only the second Lawrence's that I've seen).

The only other member of the genus Vermivora is the now extinct Bachman's Warbler, named for Audubon's confidante and a great naturalist in his own right. That species, which was a specialist of canebrake habitats in the southeastern U.S., is now extinct with the last documented observations dating back to the 1960's.

Blue-winged and Golden-winged warblers have probably long hybridized, and for whatever reasons this species complex never fully separated. Their hybridization may serve them well; in helping the Blue-winged/Golden-winged group (I don't think they should be treated as separate species) adapt to changes in the environment, much of which is man-caused. While the recessive and more fragile Golden-winged group of this species complex may die out (and I certainly hope that it does not!), at least the species in the bigger picture may carry on.