From the big questions (how many species of birds are there?) to specifics (should the Bullock’s Oriole and the Baltimore Oriole be merged into one species called the Northern Oriole?), birders have long endured a bit of confusion. It seems even the most eminent ornithologists disagree on these and similar conundrums.

In 1946, a paper published by Ernst Mayr asserted that there were  8,616 species of  bird worldwide. Today, the consensus is that there are closer to 10,000 although estimates vary widely. What happened?

In 1973, scientists decided that the two most common American orioles, the Bullock’s Oriole in the west and the Baltimore Oriole in the east, were really the same bird. Where their ranges overlapped, they mated and produced fertile young. Then, in 1995, the two species were separated again! Why?

When taxonomists combine two or more species into one, that’s called “lumping.” When they decide that different subspecies or races are really separate species, that‘s known as “splitting.”

Back in the day, a species was defined as a group of animals that were able to interbreed and produce fertile offspring in nature. Other criteria—behavior, anatomy, habitat—were also considered.

With the advent of DNA testing, the science of taxonomy radically changed. We can now look at the actual percentage of overlap between different groups of organisms. The whole concept of “species” is being redefined.

Lifers from Splits

Happily for us listers, the current trend is toward splitting rather than lumping. That means there are more birds for us to check off—and sometimes a new species turns out to be a bird we’ve already seen! This is why it’s a good idea to keep track of races and subspecies when we’re out birding.

My life list has definitely benefited from all the splitting going on. For example, the Cackling Goose is now a separate species from the ubiquitous Canada Goose, and I can count both of them. (I listed all the other extra birds I have because of recent splits at the end of this post.) On the other hand, I’ve lost potential lifers, too, such as all those Dark-eyed Junco subspecies. I still keep notes on lumped subspecies, just in case. The field is so volatile, you never know when those lumped species will be split apart again.

It’s a good idea to keep an eye on species being considered for potential splits. (Sibley’s website is a good resource.) I recently read an article about Lilian’s Meadowlark, currently a subspecies of Eastern Meadowlark found in the southwest. I wish I knew if the birds I saw in Texas were Lilian’s, but I couldn’t even tell the Easterns from the Westerns. No one was singing in January.

White-breasted Nuthatches are another potential split. I know I’ve seen them all over the country. While they are still currently considered the same species, I’m ready should the splitters decide to separate them.

Many people watch birds, enjoy their bright colors and entertaining behavior, and never make a note to record their sightings. That’s great, and I wish more people would discover birdwatching. However, if we are going to the trouble to keep a life list, it’s to our advantage to learn the subspecies too. I don’t list every single time I see a particular species (my computer would be overflowing with House Finch notes!), but I do keep track of familiar birds seen in other places. I never know when I might want that information.

Photos: The Western Scrub Jay, Curved-billed Thrasher, and Willet are all being considered for splitting.
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My Gains from Splits

• I’ve seen both the Juniper Titmouse and Oak Titmouse, the species into which the Plain Titmouse was divided in 1998.
• I’ve also seen both the Antillean Nighthawk and the Common Nighthawk it was split from by 1982.
• In 1993, Rosy Finches were divided into Gray-crowned Rosy-Finches, Brown Rosy-Finches, and Black Rosy-Finches. (They had all been considered separate species before 1976, too.) I’ve seen all three species in our local mountains.
• The Blue Grouse was split into the Sooty Grouse (along the coast from California to Alaska) and the Dusky Grouse (in the Rockies from New Mexico to the Yukon Territory). While they look very similar, their ranges do not overlap. I’ve seen several Dusky Grouse, but am still looking for the Sooty Grouse.
• The Gilded Flicker, Yellow-shafted Flicker and Red-shafted Flicker were lumped into the Common Flicker in 1973. In 1995, the Gilded Flicker was split out again. I’ve seen all three, giving me two species to count.
• Western Flycatcher was split into Pacific-slope Flycatcher and Cordilleran Flycatcher in 1989, another case where I’ve seen both birds.
• The Rufous-sided Towhee became the Eastern Towhee and the Spotted Towhee in 1995. I found them easy to tell apart.
• The Solitary Vireo was split into the Plumbeous Vireo, the Blue-headed Vireo, and Cassin’s Vireo in 1998. Plumbeous Vireos are common in Colorado, and I hope to see the other two on a trip someday.
• The Red-breasted and Red-naped Sapsuckers were split from the Yellow-bellied Sapsucker around 1982 and 1987, respectively, giving me three birds instead of one.
• The Sage Grouse was split into the Gunnison Sage-Grouse and the Greater Sage-Grouse in 2000. I’ve seen the Greater Sage-Grouse, and would love a glimpse of the endangered Gunnison while it still exists.
• The Scrub Jay was split into the Florida Scrub-Jay, the Island Scrub-Jay, and the Western Scrub-Jay in 1995. I’m still missing the Island species, a good excuse for trip to California.
• Traill’s Flycatcher became the Willow Flycatcher and the Alder Flycatcher in 1973. Check, and check.
• California Towhee and Canyon Towhee derived from the Brown Towhee. Check and check again.