Grizzly bears and Kodiak/Alaskan big brown bears used to be considered different species, and everyone knew it was B.S. They were pretty much the same animal except that the Kodiaks were somewhat larger, though not always, and there was overlap in size anyway. The species range was a relatively arbitrary line along the Alaskan coast, which would be odd since these bears can wander widely. It was like that for a long time, and even my young self could tell it was an artificial distinction when I got my first Peterson Mammal Field Guide back in middle school, yet it persisted because people wanted to believe that they were different.
Hell, when I was in middle school (my obsession was overwhelming...I was an odd kid) I got an older book from the Community College about North American mammals (it was a two volume set of huge books), and they had grizzly bears broken up into dozens of species. If you've seen the range map of the bears and know how much territory they need then you would have to assume that some species only had maybe 20 bears total, which would be quite the genetic bottleneck. But, obviously, there weren't that many species of grizzlies, just like there weren't two species of North American brown bear. In fact, when people went out and tested the genetics of the populations they found that, not only were they the same species (obviously), but that all brown bears in North America, Asia, Europe, and formerly North Africa were the same species.
Looking back, it seems obvious, right? But it persisted for years (along with things like the Kaibab/Abert's squirrel distinction) despite what now seems to be obvious simply because there was a set precedent. I blame typological species thinking and use of type specimens, but these things lasted well within the time of the Modern Synthesis.
Today I am going to look at birds that seem to be like that, you know, birds that we all know are probably the same species but don't want to say anything because it will winnow our life list down. But instead of using science and all to figure this out, I am doing this simply by impression and feel when I see them. So let's start out with some rules and notes!
-This exercise is simply by impression and is mainly for effect. Basically, this is like if you see a couple bird species and you think "come on, they aren't different species!" I am well aware of problems with species concepts. I have a master's in ecology and evolutionary biology, as well as being an ABD in the same field (yeah yeah, I didn't finish). I've read countless articles and books on the topic, seen lots of seminars and had long discussions in and out of the classroom. Now that you see my bona fides, I'll set them aside and say this is again just based on impression and if they give me a "yeah, right!" reaction.
-I won't be touching any sea birds, shore birds, hummingbirds, flycatchers, or (god help me if I did) gulls. I want this to be fun, not a torturous chore.
-This is not exhaustive.
-If they were recently separated I am ignoring it. They probably had a good reason, and...
-I am doing no background research on this at all, just going with my gut.
Ok, what are some of the red flags that make me dubious of their different-species-ness?
-They look the same, sound the same, or are only subtly different. Or, if there difference just doesn't seem meaningful.
-Abrupt species range boundaries, such that one species that look the exact same as another one just happens to end its range within an eighth of a mile of the other one.
-They seem like they are part of a cline, but the "type specimen" are from the obviously different end points.
-There is rampant hybridization. Hybridization doesn't make two species one (see coyotes and wolves), but if they look the same, sound the same and interbreed freely then you have to think "really, they are different species somehow?"
-They are the types of birds where people often have to convince themselves that they really look different.
Now there is precedent for this type of thing! Canada Geese used to be "Greater" and "Lesser" (and even more!) species, but cooler head prevailed and they were put together. Of course, science came in and said that Cackling Geese were different, but that's fine. I go with science. Also Dark-eyed Juncos used to be lots of junco 'species' until someone said "come on, really?" Juncos pretty much hit all the points above.
Birds that are classified as different species which don't seem like different species:
-Carolina Chickadee and Black-capped Chickadee. This has got to be the classic case, right? It has the seemingly artificial species boundary with little overlap, very similar appearance, a song that is learned and can be learned by the 'other species', and hybridization. Seriously, look at the species boundary! So artificial, so painfully obviously the same species.
-Northwestern Crow and American Crow. This is the pair that inspired this post! Seriously, I'll just quote Sibley (and note his obvious skepticism) on the entry for Northwestern Crow in the field guide: "Averages smaller than American with slightly lower-pitched voice, but all variation clinal. Not identifiable except by range." See, even he doesn't believe that. Look at the range too, it is the obviously artificial boundary where one starts and the other begins. Note the Northwestern Crow averages only a little less than the American, but they are both within range of each other. How the hell did this every be considered a species in the first place and why do we continue to fool ourselves about it?
-Mallard and American Black Duck (and probably Mottled Duck). Ok, I'm cheating on this one because I know that, genetically Black Ducks are absolutely Mallards. This one is tricky because males look so different that I can see why they would be considered different species, but there is precedent with the Mexican Mallard. I saw a presentation about the genetics of them a dozen years ago and we still haven't changed them. Inertia is difficult to overcome.
-Vaux's Swift and Chimney Swift. How the hell do you pronounce Vaux's? Is the 'x' silent? Once again I can read between the lines with Sibley for the Chimney Swift: "Very similar to Vaux's". They even put them together on the same flashcard! They are basically the same, one in the east, on in the west. (NOTE: there are many birds with this pattern of being basically the same except one in the east and one in the west, especially owls. I'm not going to go through all of them because it gets redundant and uninteresting).
-Greater Scaup and Lesser Scaup. First, how do you pronounce "scaup"? I've heard it "scupp", "scalp", "scawp", "scahp" and probably a few others (I go with "scahp", rhyming with pop). Anyway, these are the classic "oh, come on!" species pair, as they are pretty much the exact same (with some subtle differences), overlap in range, will flock together, and they hybridize. I go with everyone else when I identify them and play along about them having a real and meaningful difference, but I do not believe.
-Gila Woodpecker, Golden-fronted Woodpecker, Red-bellied Woodpecker.
-Red-breasted Sapsucker, Red-naped Sapsucker, Yellow-bellied Sapsucker.
-Black-headed Grosbeak, Rose-breasted Grosbeak.
-Western Tanager, Scarlet Tanager.
-Western Bluebird, Eastern Bluebird.
-All the damn buntings.
-All the black throated warblers (not blue)
These are obvious clines and almost every resource book out there gives at least a cursory nod to the fact. Don't be fooled, the birds presented in the field guides are ones that are obviously of that species; they blend into each other. If we can come to accept this type of thing with Fox Sparrows, why not with these too?
-Spotted Towhee and Eastern Towhee. See above, but Eastern also used to be a bunch more. I say lump them all!
-Tricolored Blackbird and Red-winged Blackbird. Cornell doesn't even list Tricolored, so I wonder if they don't believe either. Different species? Really? Nice try, but no way!
-Pygmy Nuthatch and Brown-headed Nuthatch. They are the exact same bird. They do live in separate disjointed areas, but that doesn't seem to matter within the Pygmy range, which is already made up of separate disjointed areas. Inconsistent logic. Same species it is!
Yes, there are plenty more like this and I'm sure there are lots of people doing research about them. I'm not looking it up (maybe another post in the future? That actually sounds fun), but the problem is the ABA has its own criteria and makes its own proclamations which may or may not be grounded in science rather than tradition.