At about 9:10 today, Glenn Walbek phoned me with this update and asked
me to post it on CObirds. I am not aware of any details.
Joe Roller, Denver
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Great discussion . . . one fairly reliable field mark that hasn't been
addressed (I think) in this thread . . .
Cave Swallow's auriculars are LIGHT and Cliff Swallow's auriculars are dark . .
. this gives the species a very different look/feel/gizz: "capped" in Cave and
"helmeted" in Cliff.
Hey, all.
Leaving aside for now the question of HOW juvenile cliff swallows are
variable, I thought it would be cool to ask WHY juvenile cliff swallows are
variable. Ask, and it will be given you:
https://academic.oup.com/auk/article/131/2/121/5148982
The preceding is a link to a 2014 paper
