East meets West meets Southwest

Photographing birds at feeders can provide some great opportunities:

Red-bellied Woodpecker (Melanerpes carolinus), Starved Rock State Park,
La Salle Co, IL 1/26/2014



This is a female Red-bellied Woodpecker.

Red-bellied Woodpeckers are closely related to two other North American species, the Gila Woodpecker of the desert southwest and the Golden-fronted Woodpecker, found mostly in Texas and south into Mexico. Where these species meet they will occasionally hybridize, but since it's so rare, we call them separate species.

Here's a Dark-eyed Junco:

Slate-colored Junco (Junco hyemalis), Starved Rock State Park,
La Salle Co, IL 1/26/2014

And here's another one:



Pink-sided Junco (J. hyemalis), Bear Creek Nature Center
El Paso Co, CO 12/21/2011

And another one:

Oregon Junco (J. hyemalis), Bear Creek Nature Center,
El Paso Co, CO 12/28/2011

And yet another Dark-eyed Junco:


Gray-headed Junco (J. hyemalis), Bear Creek Nature Center,
El Paso Co, CO 12/21/2011

Dark-eyed Juncos show extensive, rather complex geographic variation, with 12 recognized subspecies in 6 distinctive groups. Where they meet, there is extensive hybridization, so we call them the same species.

And finally, here's a Northern Flicker:



Yellow-shafted Flicker (Colaptes auratus), Illinois Beach State Park,
Lake Co, IL 9/30/2013

And here's another:

Red-shafted Flicker (C. auratus), Colorado Springs,

El Paso Co, CO 12/21/2005

 

These guys occur in 5 subspecies that segregate nicely into two groups - the eastern Yellow-shafted and the western Red-shafted. There is extensive hybridization on the Great Plains, and genes from each group appear to have penetrated all the way to the opposite coasts.

 

At one time or another, each of these critters has been considered a "good" species. In some cases the subsequent changes were due to additional information, but in most cases they were due to changing concepts of what constitutes a species. Prior to the 20th century, morphology was the primary criterion -- do these two birds look different enough? After Ernst Mayr proposed his biological species concept (1), the presence of a hybrid zone was considered evidence that two forms were the same species. Today, many observers look for genetic distances (2), or for assortative mating preferences.

This sort of shift in our concepts to some degree reflects our increasing understanding of biology*, but it also reflects the difficulties inherent in the very question, "What's a species?" Clearly, in the case of the Red-bellied Woodpecker, the different forms are good species, but equally clearly they split off from one common ancestor relatively recently (as evolutionary biologists define recent, anyways). That splitting is usually a messy process, which can take quite a long time. This means that we if we look around, we are likely to see populations of organisms that are in every stage of this process, from barely differentiated (Northern Flickers) through partially split (Juncos, Red-naped and Red-breasted Sapsuckers perhaps), through good, well-behaved species (Eastern and Western Meadowlarks). Trying to define where in the process we call them good species is kind of like deciding when a person becomes an adult -- it depends upon what criteria we're using for adulthood. As our knowledge of birds increases, the criteria we deem important in delineating species is likely to change (3), and we can expect to see the field guides change periodically for the foreseeable future.

*And not, contrary to the opinions of some birders, a conspiracy to sell more field guides as they are updated to reflect the changes.

(1) Mayr, E. 1942. Systematics and the origin of species. Columbia Univer- sity Press, New York.

 

(2) Kerr, K. C., Stoeckle, M. Y., Dove, C. J., Weigt, L. A., Francis, C. M., & Hebert, P. D. (2007). Comprehensive DNA barcode coverage of North American birds. Molecular Ecology Notes, 7(4), 535-543.

 

(3) De Queiroz, K. (2007). Species concepts and species delimitation. Systematic Biology, 56(6), 879-886.