I think the photos of the WEGR and CLGR at Stern's Lake posted in Jason Cole's checklist linked below seem to illustrate what Caleb is describing here. https://ebird.org/checklist/S85225919
John Malenich Boulder, CO On Sunday, April 11, 2021 at 11:33:19 AM UTC-6 [email protected] wrote: > Hi Mark! > > For the sake of efficiency, I'll be using WEGR to be Western Grebe and > CLGR to be Clark's Grebe. > > You would be correct that there is variation and therefore ambiguity when > it comes to the black and white pattern on the face. From my limited > experience, WEGR tends to be the species that has the most common variation > that brings facial IDs into the gray-zone, and it seems like most CLGR are > pretty straightforward. That being said, looking at a grebe from half a > mile away introduces issues, because we can't see every single bird with > close-up detail as we would like. The other primary mark that is probably > the most useful one to use year-round is the color pattern of the shoulder, > neck, and flanks. > > On WEGR, the black extends from the back of the neck to more of the base > of the neck, and that dark plumage (I say dark, because depending on the > age/molt/a bajillion random parameters, it can be black, or some shade of > gray) then goes down the shoulder close to the water. I've only been > birding for a few years, so take this with a grain of salt, but I've never > seen a WEGR in the field that did *not* have dark plumage extend down to > the shoulder that connected to the water. The dark plumage extends down the > flanks, so the bird just has a darker appearance. Where the body of the > bird meets the water on WEGR is usually dark plumage. On CLGR, there is > often much more white on the neck, and the black is restricted to the back > of the neck. The white then comes off the neck and down the shoulder, which > gives the entire front of the bird a much brighter, cleaner GISS. On adult > birds, that white/light gray extends down the flanks that are in contact > with the water. In most cases, you don't even *need* to see the head in > order to make an ID: dark shoulder always means WEGR, no need to wonder. If > where the body comes in contact with the water is pretty clearly white, > then that is most likely CLGR. > > All this being said, I should mention that WEGR x CLGR hybrids do occur > sometimes. They probably aren't super common, but I suppose it's never a > bad idea to consider this possibility in those situations when you see a > bird where all the marks are deep in the realm of ambiguity. I didn't talk > much about the bill, because although I'd imagine that's helpful on adult > birds in breeding plumage, I'm not sure how *reliable *of a mark that is. > Sure, CLGR tend to have brighter and cleaner yellow bills, and WEGR have > more dulled colored bills, but this is an even more unreliable mark to base > entire IDs off of. Just to name a few parameters that will be in constant > flux that can change the way a bill looks include lighting, feeding, and > age. > > Hope this was helpful in some way :) I'd be interested to hear what more > experienced birders do to identify the large grebes. > > *The birds are happy, and so am I* > *~Caleb Alons, Larimer County* > -- -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To post to this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/cobirds?hl=en?hl=en * All posts should be signed with the poster's full name and city. Include bird species and location in the subject line when appropriate * Join Colorado Field Ornithologists https://cobirds.org/CFO/Membership/ --- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/cobirds/0e340642-b4fc-4fc2-8cf6-a4c4968396f8n%40googlegroups.com.
