I saw two raptors ahead on the beach. They took off, and flew over me. Large, with a most unusual wing pattern: white on the inside, black on the outside. Not just the flight feathers: a clean line in the middle of the wing. Stranger still, what they dining on appears to be another of the same species. Note the beak (head is bent under).
I have looked through hundreds of birds online and found nothing resembling these, which I would have guessed to be eagles.
Then this:
I’ve seen this DTOTB before — any idea what it is?
Update: river dolphin.
Looks something like Amazon River dolphins.
I think that is correct. The dead bird is in fact a seagull, and the carrion-eaters perhaps caranchos, though images I've seen don't concur exactly with what I remember seeing. I'll just have to see them again 😉
https://en.wikipedia.org/wiki/La_Plata_dolphin
That solves that mystery — thanks!