illustration from Langdon article
The History (and Mystery) of The Cincinnati Warbler
contributed by Mike Busam
Every year we get the opportunity to see a few "hotline" birds that visit our area. Sometimes the bird of the moment is one that visits only irregularly, during irruptions that occur every few years. Other times a bird appears that hasn’t been seen in or around Cincinnati in many years—decades, perhaps. Every now and then we even get to chase a bird that has never been seen in the Tri-State. But how often does a birder experience what Dr. Frank W. Langdon did on May 1, 1880, when, during a morning of birding in Madisonville, he discovered a species that no one had ever seen before? Imagine the excitement. Your description of the bird would be the first anyone ever read. The sample you collected that morning when it finally stopped its erratic flight to preen for a moment on the tip of a maple bough would be the type specimen against which all future specimens would be measured. The best part, though (definitely the best part): it would be your warbler to name. From that moment on, wherever the scientific name of the bird was cited, your last name would trail in parenthesis the genus and species names. You'd be forever linked to a bird that countless numbers of future ornithologists and birders would look for every spring.
Dr. Langdon’s new species, which he named Helminthophaga cincinnatiensis, the Cincinnati Warbler, wasn’t a species for long. But for a while at least, like Nashville, and Cape May, and the states of Kentucky, Louisiana, Connecticut and Tennessee, Cincinnati had a warbler to call its own.
In a paper printed in the Journal of The Cincinnati Society of Natural History in 1880, Langdon described his newly-discovered warbler. The bird’s "entire upperparts, excepting [the] forehead, [are] clear, bright, olive green, with a tinge of yellowish in certain lights; quills and rectrices dark plumbeous brown, their outer webs fringed with olive green like that of the back." Langdon also noted that the forehead is bright yellow, and "bounded anteriorly by a very narrow black line from [the] lores, and behind gradually merging into the clear olive green of [the] crown." Simply put, the Cincinnati Warbler is bright yellow below, like a Kentucky or Hooded Warbler, and olive to yellow-green above. There are no wing bars, but there are distinctive facial markings. The bird has velvety black lores, which merge into dark brown eyes, before streaking narrowly through, and a black auricular patch, separated from the eye by a small yellow area. Langdon added that the feathers in the auricular patch are "black, tipped with yellowish-green, giving them a mottled appearance."
How did the bird behave? Did Langdon hear it sing or call? We don’t know. He did write "of its habits nothing is known except that it was shot while searching for insects at the end of a maple limb, about fifty feet from the ground."
Langdon concluded his description by stating "It is a little remarkable that this should be the third new species of this genus [Brewster’s and Lawrence’s Warblers were discovered in the mid-1870s] announced from the eastern United States during the past six years." Even more remarkable to the ornithologists of the time was the discovery in the early 1880s that the Cincinnati Warbler, Brewster’s Warbler and Lawrence’s Warbler were not new species, but hybrids.
Hybridization among passerines was simply not well understood in 1880. Additionally, the Blue-winged Warbler had only recently begun its northward spread and "takeover" of its closely related congener, the Golden-winged Warbler. The northward push of Blue-winged Warblers was more pronounced in the eastern U.S. than in the Ohio Valley, but wherever Blue-winged Warblers encounter Golden-winged Warblers, the same events occur. During the initial period of contact between the two birds, records of Brewster’s and Lawrence’s Warblers increase. Gradually, through a not-entirely-understood combination of competition and interbreeding, the Blue-wings replace the Golden-wings—often to the point where the Golden-winged Warblers disappear as breeders altogether. (Indeed, this could very well happen to the entire species, according to some ornithologists.) The entire process, from initial meeting to the disappearance of the Golden-wings takes about 50 years.
The type specimens of the "new" species of Vermivora, Brewster’s and Lawrence’s, were collected in Massachusetts and New Jersey, respectively. Additional hybrids were soon found in Pennsylvania and Connecticut. Unlike Ohio, these states had a fairly respectable number of breeding Golden-winged Warblers, though they were distributed locally. It took some time for scientists to recognize what was happening and to realize that when they were looking at Brewster’s or Lawrence’s Warblers, they weren’t seeing new species, but rather the results of the genetic collision between two birds they were already familiar with.
The Cincinnati Warbler is related to that dynamic avian duo and their varied hybrid offspring, but with a twist: Langdon’s warbler wasn’t merely the result of a pairing between two birds that are so genetically similar as to be, according to some, merely different forms of the same species, but an intergeneric pairing between two birds that one wouldn’t normally expect to choose each other. But somewhere along the line, choose they did, and a Blue-winged Warbler and a Kentucky Warbler got together and made at least one Cincinnati Warbler.
That’s not to say that similarities between the Cincinnati Warbler and the two birds we now know produced it were overlooked. In his description of the Cincinnati Warbler, Langdon wrote that Dr. Elliott Coues, who examined the specimen on Langdon’s behalf, believed "its relations are mainly with Helminthophaga pinus [Blue-Winged Warbler], although in the concealed black of vertex and auriculars it slightly resembles certain plumages of Oporornis formosa," or Kentucky Warbler. Similarities in facial features aside, Coues and Langdon ruled out an unusual looking Kentucky Warbler because of the Cincinnati Warbler’s "smaller size, dissimilar proportions, short tarsi, yellow forehead, and white margin to [the] outer tail feathers." They also felt the bird wasn’t an oddball Blue-winged Warbler because of it’s large size, lack of wing bars, and the presence of black auriculars. The potential that this was a Blue-winged x Kentucky hybrid crossed their minds, but, according to Langdon, given what they knew at the time, the "suspicion of hybridism" was considered "inadmissible."
Had Langdon and Coues known in 1880 what we know today about genetics and hybridization, they certainly would have been more suspicious about the parentage of the Cincinnati Warbler. If it were encountered today, the Cincinnati Warbler’s black auricular patch, which looks like it has been cut right off the head of a Kentucky Warbler, and the mix-and-match Kentucky and Blue-winged Warbler characteristics clearly would mark this bird as some kind of a hybrid, not a new species. (Then again, it might be even easier to quickly write off such a bird as merely a strange looking warbler, a "UFO," and then move on to something a little more obvious.) But given what scientists knew then, it’s understandable that the Cincinnati Warbler was thought to be a new species in the genus we know today as Vermivora.
The origins of the Cincinnati Warbler will remain a mystery. That much we’re sure about. We’ll never know what led a Kentucky Warbler and a Blue-winged Warbler to mate, nor where they hatched the Cincinnati Warbler and his siblings, nor if any of those hybrid birds survived long enough to breed. Like any good mystery, though, the mystery of the Cincinnati Warbler has a final and intriguing chapter: in 1948, 68 years after Langdon discovered the first Cincinnati Warbler, an ornithologist named Frank McCamey collected a second bird in Cass County, Michigan, 18 miles north of the Indiana state line.
On May 19, 1948, while birding in a mature oak woods, McCamey heard a "puzzling song—a loud kuh-chee, kuh-chee, kuh-chee, which rang through the woods like the song of an Ovenbird. The syllables were repeated with even rhythm and unvarying pitch."
When McCamey located the warbler he immediately realized it was not an Ovenbird, but a bird that resembled a Blue-winged Warbler, minus the white wing-bars. McCamey observed the bird for nine consecutive days. Unlike Langdon’s account of the Cincinnati Warbler type specimen, McCamey recorded the Michigan bird’s behavior. As was the case with Langdon’s warbler, McCamey’s warbler was discovered high in a tree. It preferred to perch between 20 to 60 feet off the ground, and would drop down into a 20-foot high undergrowth to feed. "It devoted much of its time to singing," writes McCamey, "and probably did not have a mate." Furthermore, when foraging in the under-growth, the warbler "moved rather slowly, occasionally singing without flying to one of its regular song-perches." McCamey searched for a nest and a possible mate for the bird, but had no luck. There were plenty of singing Blue-winged Warblers nearby the wooded area in which McCamey’s bird spent its time, but McCamey never saw the warbler attempt to attract or interact with those birds. Finally, on May 28, McCamey collected his mystery warbler.
Shortly after McCamey collected the bird, an ornithologist in Ann Arbor, Dr. George M. Sutton, compared the Michigan bird with the Cincinnati type specimen, which he borrowed from the Cincinnati Museum of Natural History. The type specimen and the Michigan bird are very similar in appearance. The Cincinnati bird is a little larger; other than that, the main difference between the two birds is that the Michigan bird lacks a distinct, black auricular patch, while retaining a black loral streak that runs through the eye, similar in appearance to the loral streaking on a Blue-winged Warbler. McCamey and Sutton were fairly certain that the bird’s parentage was at least one-half Blue-winged Warbler, and that the other likely candidate was either a Kentucky or a Mourning Warbler. Kentucky Warbler was all but ruled out, in large part because in 1948, there were only three records of that warbler in Michigan, while Mourning Warbler was known to breed just north of the location where the Michigan warbler was collected. Additionally, the size of the Cincinnati specimen was closer to that of a Kentucky Warbler than was the smaller Michigan bird. McCamey concluded that "at least provisionally" the Michigan bird was a cross between a Blue-winged Warbler and a Mourning Warbler. So lightning didn’t strike in exactly the same place twice (though it came very close!), and the Cincinnati Warbler discovered by Dr. Langdon in 1880 remained the only one of its kind.
Given the oddity of these two very similar hybrids, one had to know that the issue of their genetic origins wasn’t going to be settled that easily. In 1988, Gary R. Graves of the Smithsonian Institute compared size and plumage characteristics of the Cincinnati and Michigan specimens; in addition he ran measurements on numerous specimens of pure Blue-winged, Kentucky, and Mourning Warblers. His findings affirm that the Cincinnati bird is, indeed, close in size and plumage to a Kentucky Warbler, and he hypothesizes that this is because it is a first generation hybrid. Graves put the Michigan bird under a microscope and discovered that it had "black barbs on the edges of a few auricular feathers"—a "Kentucky-like" characteristic. The Michigan bird is, as McCamey noted, closer in size to a Blue-Winged Warbler, but the other half of its parentage isn’t necessarily a Mourning Warbler, particularly given the presence of auricular coloring, albeit invisible to the naked eye. At the conclusion of Graves’ article, he suggests that the lack of an obvious auricular patch and the bird’s smaller size are due to the fact that, unlike the Cincinnati Warbler type specimen, the Michigan warbler isn’t a first generation Blue-winged x Kentucky Warbler hybrid. Instead, the Michigan bird could very well "represent the progeny of [a first generation] hybrid back crossed with a pure [Blue-winged Warbler]." It’s likely, then, that there hasn’t been just one Cincinnati Warbler, but at least as many as two or three. Who’s to say it couldn’t happen again? And if it does, maybe some lucky Tri-State birder will get to discover another Vermivora cincinnatiensis (Langdon): The Cincinnati Warbler.
Note from Mike Busam: I’d like to thank Alan Brushaber who runs the Southeast Michigan Birding home page and the subscribers of the University of Michigan Birding List for putting me in touch with Janet Hinshaw, librarian of the Wilson Ornithological Society, who sent me a copy of the hard-to-get Frank McCamey article that first appeared in The Jack-Pine Warbler. Thanks too, to Ned Keller for finding a copy of Dr. Langdon’s report on the Cincinnati Warbler from an 1880 issue of the Journal of The Cincinnati Society of Natural History. Space considerations have made it impossible to cite all the sources I used and quoted in this article, but if you send me an e-mail at firstname.lastname@example.org I’d be happy to send you a fully annotated version, suitable for framing (or critiquing!).