I saw this Horned Grebe, probably a juvenile, a few yards off the northern shore of the park a half hour before sunset. With help from the low slanting light, the bird’s red eyes glared as if powered by an LED. It looked to be solitary, and after it dove, it escaped my view entirely.
I’ve looked online for cogent explanations of the red eye, with no success. More than 30 species of birds have red eyes. Some of them are divers, like grebes, others never go near water. Many divers do not have red eyes. In some birds, eye color changes as they reach maturity. In the grebes, not so much. The takeaway seems to be that evolution yields random mutations, and some work just as well as others, so we see a diversity of features all serving similar functions.