My opinion on my super brief view was Turkey Vulture, but I had seen so little I had zero confidence and logged it as Cathartes sp. Then another observer said he saw the white flashes on the upper side of the primaries and considered it LYH. The first photos I saw were hard to interpret, but with more photos I felt it was Turkey - but still doubted a bit, so I appreciate the opinions.
For what it's worth, I shared these photos on the FB group "Advanced Bird ID" and to a few friends. The overwhelming opinion including a couple of S America's top ornithologists, is that you can unequivocally ID it as a Turkey Vulture. Here are some of the comments if anyone is interested:
"These images strike me as being of Turkey Vulture. A Lesser Yellow-headed would have the palest part of its head be below and in front of the eye, not on the crown or nape, even when in shadow. Turkey Vultures have pale napes in some subspecies, and this can give them a "multicolored head," even though they lack the blues, greens, and yellows of a Yellowhead."
"I think the challenge here is in ruling out a juvenile Lesser Yellow-Headed. I agree that the bird immediately strikes me as a Turkey Vulture, but is that just because I don't spend enough time looking at young Lesser Yellow-Headeds? At what age do they lose the white nape? For what it's worth, I don't see any obvious wing molt that would age this bird as older-than-juvenile."
"I’m not familiar with the Lesser Yellow-head species, but a look at Macaulay Library shows juveniles to have dark bills, which this bird obviously doesn’t have. It is also missing/regrowing a primary on both wings, so shouldn’t that indicate at least a second year? Both species show 6 longer “fingers” in full plumage. This bird shows five."
"The upper photo shows brown along the leading edge of the wing, so that would suggest the upperparts were brown. I still would go all-in on Turkey"
"I also still think it's a Turkey Vulture, but I'm not sure brownness of upperparts is a reliable mark to separate Turkey from the Yellow-headeds. I'm still curious if anybody knows when young Lesser Yellow-headed gain their adult head patterns."
"That is a classic ruficollis (Tropical) Turkey Vulture, which is what is common in Buenos Aires. Dull reddish face and pale nape. Lesser Yellow-headed has a dark mask."
