The word “endemic” has always seemed vague to me. Oxford Languages offers this definition: 2. (of a plant or animal) native and limited to a specific area. When a birder uses the word, we are usually referring to a species that may be found mostly or exclusively in a country. That means the huge country of Mexico boasts (according to one list) 127 endemic bird species, while only 6 are popular birders’ destinations in Costa Rica. It doesn’t seem fair.
I’ve seen about a fifth of Mexico’s endemic birds, almost all of them right here in the state of Michoacán. But one of Michoacán’s endemics beats most of them for sheer endemism; its entire range can easily fit within just two of Costa Rica’s small provinces. The Black-polled Yellowthroat is usually found only in three bodies of water: Lakes Pátzcuaro and Cuitzeo, in Michoacán, and the Ciénega de Lerma (Lerma Marsh), in Mexico State. Here are some of my best pictures of a man Common Yellowthroatwhich is found throughout North America, and is a male Black-polled Yellowthroat. Females are much alike, but their songs are easy to tell apart.
Common Yellowthroat
Black-polled Yellowthroat: It’s all on the forehead.
Now, when a species is only found in three bodies of water, it must be disturbing when one of those, Lake Cuitzeo, actually dries up, and the water levels in the other two are greatly reduced. I worry about my oh-so-special little friends. How about our Black-polled Yellowthroats live?
Fortunately, I now have some answers. Last month, I took four of my biologist friends to a small reservoir within the city limits of Morelia. This reservoir is not usually a very bird-friendly body of water, despite its beautiful stands of cattails and reeds. But I wanted to see if some of the waterfowl of Lake Cuitzeo might not migrate there when they lost their usual wintering grounds. And indeed they have; we found 7 wild duck species, where usually there are none.
But more excitingly, an ornithologist we all know has also reported the presence of three Black-polled Yellowthroats moving in the cattails of this reservoir. This is the first report ever for this site. Can we find them too? We really did!
Twelve days later, and we all flew to Lake Pátzcuaro for our region’s only Christmas Bird Count. Lake Pátzcuaro is not deep, but it seems to be about twice as deep as Lake Cuitzeo, and does not dry up like that lake from time to time. However, so far the lion’s share of Black-polled Yellowthroat sightings occur in a place I know, Puente de Jarácuaro, on the southern shore of the lake. As it turned out, that was the beginning of our team at CBC, and it did not disappoint. Cattails grow from the now dry soil. But the Yellowthroats still turned quickly.
But this year, CBC only included a total of ten observers, so half the lake shore was ours. And in the end, we found it Black-polled not only in the common area, but also in two other sites, where it has not been reported. More evidence of resilience?
As I was preparing to write this post, I learned that a very reliable birder had also seen the species in another lake, Lake Zirahuen, for the first time. It was also reported a second time by Lake Yuriria, just across the state border in Guanajuato — but due to some anomalies in that report, I don’t have much faith in its veracity, although the lake is certainly a reasonable destination for the “refugees” of Cuitzeo.
However, it is very encouraging to know that a very site-specific and water-dependent species can fly over many kilometers of dry land to find the habitat it depends on. And who knows, maybe it can use this crisis to find some new breeding grounds, to ensure its survival in the near future?
