I cannot agree more thoroughly with Ted's cautions about Merlin, and, particularly, his cautions once we get into the warbling-vireo season. I, too, find many warbling vireo songs far from cut-and-dried enumerators of species, and please, please, please, don't take Merlin's word on it as gospel. Save the recording. Save the spectrogram. Both species have been detected during the breeding season at Barr Lake, and there's absolutely no guarantee against warbling-vireo hanky-panky. We want our understanding of the occurrence parameters in eastern Colorado to be based on provable facts, not intuition, supposition, or blind trust in technology.
Enjoy,
Tony Leukering
Denver
On Sunday, February 15, 2026 at 7:03:21 PM UTC-7 Ted Floyd wrote:
Thanks, everybody, for the recent discussions about documenting crossbills and warbling-vireos in Colorado. Inspired by a recent report from Eric DeFonso of crossbills at the Green Mountain West trailhead, near the high point along Flagstaff Rd., Boulder Co., I went up there myself earlier this sunny Sun., Feb. 15. But it was windy—too windy, really—at Green Mountain, so I retreated downslope a bit to the comparatively leeward Long Canyon trailhead, where the wind wasn't nearly as strong. And, oh yes, there were crossbills there.
As far as I can tell, all were type 2 ("ponderosa pine") red crossbills. And how do we know they were type 2s, as opposed to type 3s, or type πs, or, for that matter, Cassia crossbills? Because of the diagnostic sound spectrograms of birds like this one, and these two, and also these two or three. Which brings us to Mark Obmascik's recent musings on the identification of Cassia crossbills in Colorado. I concur with Mark: It is essentially impossible to credibly identify birds in the "Red Crossbill complex" in Colorado without an assist from technology. But there's a big "but" here: I didn't fire up Merlin, not even once, the whole time I was up Flagstaff this morning. Rather, I made recordings, studied the spectrographic output, and confirmed that all the crossbills up there were type 2s. Maybe that's a mere quibble, differing exegeses of "crossbill theology." But I dunno, it feels different, to me, to say: "Because Merlin said so" vs. "Because I figured it out on my own." In any event, it remains the case that we require technology, in the form of sound spectrograms, whether Merlin-vetted or human-vetted, to get the ID correct here in Colorado. Which, as Mark implies, is a paradigm shift. Culture shock, even.
I actually heard more "toop notes" up there than flight calls. Type 2 "toop notes" sound like this, and also like this. They are clear and ringing like flight calls, and I can totally see that one might imagine they're the flight calls of a "good" crossbill—a Cassia perhaps, or one of the rarer (for us) red crossbill types other than type 2. But they are spectrographically unlike the flight calls of any crossbill expected in Colorado. This is fun: If you jack up the type 2 red crossbills flight call a kilohertz or two, you get pygmy nuthatch; and if you raise it another kilohertz or two, you get hairy woodpecker; and if you're on a boat at sea, your hairy woodpecker is become a red phalarope. Who'da thunk?
Along with the type 2 flight calls and "toop notes," there was full-on crossbill song up there. Sorry about the wind noise; someone musta left the gate open up at Green Mountain. Anyhow, it's a cool song. I put in my notes that the run-on, "random" song of the type 2 red crossbill sounds a bit like the song of a dipper or even a woodcock.
I made videos, too. They're not great, but they get the job done: They show type 2 red crossbills caught in the act of giving both flight calls and "toop notes." Yes, flight calls are routinely given by perched birds.
And some photos. While probably of limited utility for field identification, photos of crossbills can contribute importantly to a recent finding, both surprising and counterintuitive, by Blanca Fernández-Eslava and collaborators that male crossbills acquire a female-like plumage aspect as they age. That is quite the opposite of the "standard model," wherein female birds acquire male-like plumage aspects as they age; examples in Colorado are the wood duck, western tanager, and Wilson warbler.
Anyhow, here are a few crossbill pics from this morning:And for fans of weird & unexpected catchlights:
The Douglas-fir cone crop up there was insane, which insanity I duly iNatted. (And which Owen Robertson already has research-graded. Thanks, brother.) You heard it here first: If type 4 ("Douglas-fir") red crossbills make their way to Colorado anytime soon, it's going to be up Flagstaff. Okay, it was Eric who put that idea in my mind, not gonna lie. Anyhow, there must be untold millions of juicy douglas-fir cones up there. The nuthatches seemed happy about it. So did the siskins.
Back to crossbills. A possible take on the preceding: Okay, that's all well and good, but can't we just say "Red Crossbill," at least in the Front Range metro region, and be done with it? Yes, that is true. I, personally, think it is a worthwhile challenge to try to figure out the different types, but, for now, we treat them all as the same species. Although...what about Cassia crossbill?? It's not far at all, the way the crossbill flies, from Grand Co. In fact, Grand & Boulder cos. share a long border. So why not?
In any event, that same take isn't gonna cut it come warbling-vireo time, not even three months out. Because the two warbling-vireos are indeed full species, according to current science, and both of them are here in the Front Range metro region. David Suddjian reminds us that the songs of Eastern and Western warbling-vireos are distinct, and I don't disagree. But I am wary of our ability to tell them apart, especially where they overlap, as here. Do they differ, to our human ears, between Nevada and New Jersey? Sure. Between San Miguel Co., Colo., and New Jersey? Yes, I would say so. But all up and down the I-25 corridor, from Ft. Collins to Pueblo and beyond, where most of us live and bird? I'm not convinced of that. I've been studying these birds' songs intensively for close to 20 years now, and I simply don't trust my ears, or, let's be honest, my brain all that much. I think it's probably true that there are some, well, no-brainers in the mix. But birds on migration? Birds exposed to the "wrong" vireo's song? Hybrids or intergrades, perish the thought? I imagine there's an awful lot of that going on here. And then mix in all the undeniable subjectivity and suggestibility at play in the human engagement of the natural world, and...yeah. Speaking for myself, I'm not good enough! I'm either going to upload spectrogram-supported sound recordings to my eBird checklists, or I'm going to happily and proudly call my warbling-vireos unidentified.
But can we, please, pretty please, agree on one thing? "Merlin" isn't adequate for the ID. It really isn't. And please keep in mind: I am one of the loudest champions of Merlin. It's a magnificent guide, pedagogically brilliant, informing and inspiring millions of peeps who might not otherwise notice birds. Merlin is all those things. It really is. But, again, Merlin is, in the first and final analysis, a guide. A suggestion, a recommendation. And so, as the old saying goes, we "trust but verify." The great thing is, Merlin makes it easy! Merlin wonderfully outputs spectrograms, and saves the audio, for every single bird it provisionally identifies for you. When Merlin says "Eastern Warbling-Vireo" (it will actually say "Eastern Warbling Vireo," without the hyphen, but that's a matter for another day) or "Cassia Crossbill" or even "White-winged Crossbill" or, what the heck, "White-winged Tern," think of it the way you might inform the clerk at Buc-ee's in Berthoud that you're holding a winning Colorado Lottery ticket. Great—but you'd better be prepared to produce the goods: a valid permutation of lottery numbers for the cashier, or the spectrogram for your friendly neighborhood eBird reviewer. And don't even get me started on "photos," or, in the case of crossbills and warbling-vireos, "recording." As in, "lotto ticket," am I right?
Alrighty, I've just now been reminded—re-reminded, actually—that I promised to go pick up the Chinese food, getting cold now, at Mr. Sake Sushi & Grill. I'm Audi...
Ted FloydLafayette, Boulder Co.
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