If you have birded very long, you are probably aware that members of closely related bird species, when their ranges overlap, sometimes love each other very much, and have babies. Some even do this so often that images of their hybrids will be included in bird guidebooks. When this happens particularly often, such hybridization processes can result in entirely new species.
Here in central Mexico, we have one such case that is so notable that it has been the subject of a good deal of scientific study. One recent article, “Hybrid zone or hybrid lineage”, refers to the issue in its subtitle as “Sibley’s classic species conundrum in hybrid Pipilo towhees”. The conundrum in question is the affirmation by the ornithologist Charles G. Sibley, way back in 1950, that all Spotted Towhees in western central Mexico are the product of a hybridization gradient between the southwestern Collared Towhee, Pipilo ocai, and the eastern Mexican race of the true Spotted Towhee, Pipilo maculatus. (Back then, Sibley used the name “Red-eyed Towhee” for what we call Spotted Towhees today.)
I have, unfortunately, not yet seen a Collared Towhee, even though they supposedly occur in my neck of the woods. Fortunately, I have great birder friends; these fantastic photos are by Alberto Lobato and René Valdez. Note the white throat patch above a black collar, the orange mohawk crown, the olive back, and the only slightly dusky flanks.
In contrast, the classic Spotted Towhee of the western U.S. and eastern Mexico has an all-black head, a black back with bright white spots, and orange flanks. This image is mine, from the central Californian coast.
Our local variant of the Spotted Towhee, currently called the (Olive-backed) Spotted Towhee, looks different than both. But upon studying the above photos of Collared Towhees, I can see that Sibley may well have been right. Our birds have the black head and reddish flanks of the classic Spotted Towhee, and the spotless olive back of the Collared Towhee. So are they a subspecies, or a hybrid intergrade?
To make things even more complicated, our possibly hybrid Olive-backed Spotted Towhees can hybridize even further with the Collared Towhee. Until recently, I had only seen a few examples of this. All were distinguished by the subtle differences of a more greenish back of the head, slightly lighter flanks, and a hint of the Collared Towhee’s reddish crown.
The reason I am writing about this subject now, is that just this week I finally saw my personal holy grail of hybrid towhees. The lighting did not allow me to see the color of this bird’s crown. And it never did give us the full-frontal view that would have been so helpful. But my few photos left no doubt; this bird had a black color, a white throat patch, and just a hint of a white line above the eyes. This was a clear hybrid Pipilo maculatus x ocai. In fact, if Sibley’s theory from long ago is correct, this bird could well be called a hybrid hybrid.
I should probably add a personal confession at the end of this post. Twice, in 2019 and 2022, I complained on this site about having to use the name Spotted Towhee for our locally spotless birds. I have even begged, with no scientific basis, for a taxonomic split, if they wouldn’t change that name. I have accused bird-namers of being biased to their United States experience of birds. (Admittedly, that is still true for the Summer Tanager, which we only see here in the winter.) But my research for this post has shown me that this problem may be much more complicated. In fact, if you move east from Morelia towards lands occupied by traditional Spotted Towhees in eastern Mexico, you will apparently find Olive-backed Spotted Towhees very similar to mine… but with light spots on their wings, growing ever clearer as you move towards the rising sun.
I humble myself before the complexities of the natural world.
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