The goose/angler interaction made me laugh, and somehow motivated me to think about the Snowy Egret. Possibilities come to mind:
(1) all snowy egrets have this breeding plumage briefly, and I've never noticed it before;
(2) somehow just the feathers at the back of the head were stained when the bird was foraging in dark-colored water;
(3) a genetic anomaly in this particular bird that affects just the feathers on the back of the head;
(4) hybridization with Cattle Egret (I don't even know if that's possible);
(5) disease affecting the feathers at that location;
(6) insects / mites / parasites affecting the feathers at that location;
(7) the bird perched with the back of it's head subject to an exhaust fan from an industrial facility that expels a dark contaminate
(I saw a pink-colored Rock Pigeon once, and a half hour later, saw it's roost at a fiberglass batt manufacturing plant);
(8) evolution in action; the bird in the photograph will be more successful than it's peers;
(9) something else.
eBird has about 150,000 photos of Snowy Egret; I didn't go through all of them, but here are some interesting photos:
(what's going on with this bird?)
(this might just be lighting)
(how staining at the back of the head might occur)
(maybe lighting again)
(lighting ?)
(that was just for fun...)
(this last photo makes me think: option 10: straw colored plumage at Snowy Egret back-of-head is variable)
Thanks for a great post, Ted Floyd, and motivating me to learn stuff!