BIRDING BY HINDSIGHT: A Second Look at Splitting

You probably don't have the time to read this, considering you're probably still busy sifting through all your old trip lists and other records for any mention of Canada Geese. ("Now, was that flock of geese I remember from 1979 near Clontarf. . . .or was it in 1989 in Flom. . . .and were they really small enough for me to add Cackling Goose to my Swift – or Norman – County list?")

So, were you caught by surprise when the A.O.U. split Cackling Goose from Canada a few months back? If you were around decades ago when they split the dowitchers, separated Thayer's Gull from Herring, and divided Traill's Flycatcher into Alder and Willow, were you ready to say what the status was of these "new" species in Minnesota and on your personal lists?

Or, what about when certain loons, golden-plovers, vireos, and thrushes were split not that many years ago? Was anyone prepared to declare whether or not Arctic Loon, Pacific Golden-Plover, Cassin's and Plumbeous vireos, and Bicknell's Thrush had ever shown up in Minnesota if we had always just assumed they were all Pacific Loons, American Golden-Plovers, Blue-headed Vireos, and Gray-cheeked Thrushes respectively? And, for that matter, what did we really know about the status of Clark's Grebe and Spotted Towhee when they were split from their respective default species?

Keeping track of birds, whether it's a science or sport, has always been based primarily on the species level of these animals. So, it matters greatly to us when the name Rock Dove is changed to Rock Pigeon, when waterfowl and gallinaceous birds are to be listed first before the loons, and especially when the A.O.U. says there is more than one species of honker to include on the lists we construct.

Change is inevitable, and there is a lot more to come, whether or not we're prepared for it. If anything, it seems the rate of change involved with listing bird species will accelerate. It's not so much that ornithologists are discovering that much more about a bird, it's mostly that they're debating the basic definition of the word "species." It's the old-school Biological Species Concept (involving the tendancy to lump birds and describe geographic populations as subspecies) vs. the newer Phylogenetic Species Concept (involving the tendancy to split and define those populations as separate species). In recent years, the pendulum has been swinging the splitters way.

Accordingly, get ready for more splits in the coming years, not to mention more changes in nomenclature and sequence on the checklist. One way to prepare for this is to take a second look at The Sibley Guide to Birds, and you'll find many species accounts which delineate differences primarily based on geographic populations. These may well signal future splits, and, if we are aware of these and take more careful note as we encounter these birds now, we won't have to guess as much later when retroactively attempting to reconstruct lists and define the Minnesota status of splits after they become reality.

Of course, not all potential and future splits are discussed in Sibley and included below, and certainly some of these entries will be false alarms. Other authors have other ideas. Note that most of these birds differ in both appearance and vocalizations, and that many of these geographic differences involve eastern vs. western North America. Not listed below are those birds which, if split, would probably not involve the Minnesota checklist. But I do include those birds involving a potential split breeding well beyond Minnesota's borders if it might occur here as a migrant or stray.       

The page numbers refer to Sibley's book, where you'll find at least some basic information about these:


Greater White-fronted Goose (p. 77) - Three forms nest in the tundra and taiga, and at least two of these probably pass through Minnesota.

Canada Goose (p. 74-75) - Yep, as mentioned in the previous Hindsight article, brace yourself for what many think will be some additional splits!

Brant (p. 76) - Years ago they were all just Brant, then they were split into two (with both hrota and nigricans documented in Minnesota), then lumped again, and now – guess what – many authorities say there are three species! Besides Sibley, also see North American Birds 58:180-185.

Tundra Swan (p. 73) - Some think the Eurasian form, Bewick's Swan, could be a separate species. No Minnesota records, perhaps, but who's been looking?

Green-winged Teal (p. 88) - Formerly, the European/Eurasian Teal was a separate species, then it was lumped, and now, naturally, it's thought to be separate again. Like the Bewick's Swan, it's a no-Minnesota-record-but-who's-been-looking bird.

Common Eider (p. 94) - If you're lucky enough to turn up this accidental some year, take careful note of its appearance so you know which Common Eider "species" it is.

Great Blue Heron (p. 60) - Here we go again: the Great White Heron was separate, then lumped, so isn't it bound to be split again? There are records of this form wandering to northern states.  

Red-tailed Hawk (p. 122-123) - With so many plumages and populations, can a split be far behind? (Remember when Harlan's was a separate species?) Besides Sibley, also see Birding 33:436-446 and 36:500-506, and Hawks of North America by Clark and Wheeler.

Willet (p. 172) - The Western Willet seems more likely, but who's to say the Eastern "species" couldn't wander here?

Whimbrel (p. 174) - Besides Sibley, also see North American Birds 53:232-236.

Short-billed Dowitcher (p. 191) - Three subspecies/populations have long been recognized, with hendersoni the default migrant here. But could the other two, griseus and caurinus, pass through Minnesota as well, and could they be separate species?

Mew Gull (p. 212-213) - All three Minnesota records seem to pertain to the West Coast form brachyrhynchus, but the European form canus seems a possibility on the Great Lakes.

Herring Gull (p. 216-217) - The Yellow-legged Gull, an East Coast (and perhaps Great Lakes?) rarity from Europe, has already been split, but still more Herring Gull splits seem inevitable. Besides Sibley, consult Gulls of North America, Europe, and Asia by Olsen and Larsson (not recommended for the faint of heart!).  

Lesser Black-backed Gull (p. 225) - Besides Sibley, also see Birding 27:282-290 and 27:370-381.

Common Ground-Dove (p. 259) - Is the lone Minnesota record a bird from the Eastern or Western population?

Downy Woodpecker (p. 312) - This and the following two woodpeckers breeding out west look different from those in Minnesota, and it's conceivable they might wander this far east in migration.

Hairy Woodpecker (p. 313) - See above, under Downy Woodpecker.

American Three-toed Woodpecker (p. 314) - See above, under Downy Woodpecker.

Northern Flicker (p. 318) - They already lumped and re-split the Gilded Flicker, so why not do the same with the Red-shafted?  

Willow Flycatcher (p. 326) - See Black-capped Chickadee.

Bell's Vireo (p. 345) - See Black-capped Chickadee.

Warbling Vireo (p. 344) - Rumors of an East-West split, based mainly on song differences, seem especially credible.

Gray Jay (p. 356) - See Black-capped Chickadee.

Western Scrub-Jay (p. 352) - No Minnesota record yet, but there is potential for one – and will it come from the Texas or Arizona population?

Horned Lark (p. 363) - A half dozen or so populations/forms have long been described, but with so many involved any splitting here could be messy.

Purple Martin (p. 365) - See Black-capped Chickadee.

Cave Swallow (p. 369) - Like the scrub-jay, there is good potential for a first state record and for a split. If and when one arrives here, it will probably be from Texas, but note the strays on the East Coast seem to be Caribbean in origin.

Black-capped Chickadee (p. 374) - Only chickadees of the Eastern population should breed here, but in some years lots of chickadees are noted migrating down the North Shore: perhaps some are from the two Western populations/"species." Several other passerines on this list have a similar situation: only one form (typically the Eastern) breeds in Minnesota, but other forms (i.e., potentially split species) breeding elsewhere (typically in the West) might pass through here during migration.  

White-breasted Nuthatch (p. 381) - See Black-capped Chickadee.

Brown Creeper (p. 383) - See Black-capped Chickadee.

Bewick's Wren (p. 385) - When this Accidental turns up, is it the Eastern "species" or a bird from the Southwest?

House Wren (p. 386) - See Black-capped Chickadee.

Winter Wren (p. 387) - See Black-capped Chickadee.

Marsh Wren (p. 389) - An East-West split, based mostly on vocalizations, may be inevitable, with both possibly breeding in Minnesota?

Golden-crowned Kinglet (p. 394) - See Black-capped Chickadee.

Blue-gray Gnatcatcher (p. 397) - See Black-capped Chickadee.

Northern Wheatear (p. 399) - Did the two vagrants which strayed here come from Alaska or eastern Canada?

Veery (p. 406) - Besides Sibley, see the series on thrush ID in Birding 32:120-135, 32:242-254, 32:318-331, and 34:276-282.

Swainson's Thrush (p. 407) - See Veery.

Hermit Thrush (p. 409) - See Veery.

Curve-billed Thrasher (p. 413) - There are three Minnesota records and strong support for splitting this into two species.

American Pipit (p. 421) - Besides Sibley, also see North American Birds 56:388-398.

Orange-crowned Warbler (p. 427) - Of the four populations, the Taiga form should predominate here in migration.

Nashville Warbler (p. 430) - See Black-capped Chickadee.

Yellow-rumped Warbler (p. 436) - Here's another one of those split-lumped-split possibilities, and there are several records in migration of the Audubon's form.

Yellow-throated Warbler (p. 444) - If the white-lored and yellow-lored forms are split, Minnesota might have records of both.

Palm Warbler (p. 441) - Unlike the chickadees et al., those breeding here are Western, with a potential for the Eastern "species" in migration.

Common Yellowthroat (p. 452) - See Black-capped Chickadee.

Wilson's Warbler (p. 454) - See Black-capped Chickadee.

Yellow-breasted Chat (p. 457) - Rarely nests in the state, but there may well be records of both Eastern and Western birds.

Summer Tanager (p. 462) - Even rarer than the chat as a breeder here, this is yet another possible East vs. West split.

Spotted Towhee (p. 474) - Just when we were getting used to separating this from Eastern Towhees, it seems a second Spotted Towhee may achieve full species status.

Brewer's Sparrow (p. 484) - Only a couple records in Minnesota, but were they Brewer's or Timberline sparrows? Besides Sibley, also see Birding 28:374-387. For this and the other sparrows listed here, consult The Sparrows of the United States and Canada or Sparrows of the United States and Canada: The Photographic Guide by James Rising.

Savannah Sparrow (p. 490-491) - See Rising's sparrow guides.

Fox Sparrow (p. 496-497) - Also see Birding 31:508-517 and 32:412-417.

Song Sparrow (p. 498) - See Rising's sparrow guides.

White-crowned Sparrow (p. 495) - Also see Birding 27:182-200.

Dark-eyed Junco (p. 500-502) - After four species were lumped into one a few decades ago, it seems high time for some splits. Besides Sibley, also see Birding 34:432-443 and 35:132-136.

Painted Bunting (p. 469) - Eastern and Western populations exist, and we don't know from which direction our strays come.

Brown-headed Cowbird (p. 510) - That's right, two or perhaps three distinct populations of this beloved bird exist!

Bronzed Cowbird (p. 511) - No Minnesota record yet, but there is potential for this (these?) species to stray this far north.

Gray-crowned Rosy-Finch (p. 526) - Both coastal and interior forms have been documented in Minnesota.

Pine Grosbeak (p. 525) - Three populations which differ in both plumage and vocalizations are involved.

Purple Finch (p. 528) - See Black-capped Chickadee.

Red Crossbill (p. 530-531) - For years, there has been serious talk about splitting this into as many as nine (!) species, based on range, vocalizations, bill size, and food preferences. Perhaps three or more of these occur in Minnesota. Besides Sibley, also see Birding 27:494-501.

Hoary Redpoll (p. 533) - As if telling a Common Redpoll from a Hoary isn't hard enough, there is talk of two Hoary Redpoll species, hornemanni and exilipes, both of which occur in Minnesota.

Lesser Goldfinch (p. 535) - No Minnesota record yet, but it is overdue, and hopefully the documentation will include whether it's the black-backed or green-backed form in case there is a split.

Evening Grosbeak (p. 524) - The calls of Western and Eastern birds clearly differ and may represent a compelling reason for a split.

*          *          *

Sixty-eight potential splits?! I'd say that's more than enough for now – certainly more than I would have guessed before I looked into this. Let's hope, though, that many of these never come to pass, otherwise there will be lots of ID headaches as a result: splitting headaches, that is. As Sibley points out, separating most of these forms in the field is a very daunting task and involves distinguishing very minute differences: splitting hairs, so to speak. (I have to wonder if any mammalogists face anything similar: you know, like splitting hares?)