1. Not all environments provide unlimited food at all times. Don't forget, in Australia, parrots are often considered agricultural pests. Until significant farming took place, they didn't have such an availability of food as they do now. Macaws in the Amazon have to eat clay to be able to deal with the toxins in their environment. Picking undigested food out of their poop may provide an advantage, the clay having leached many of the toxins out already.
2. Many parrots are ground birds (African greys have a digging instinct that's hysterical) or live in such large groups that poop is unavoidable (budgerigars).
3. Our African greys are fastidious about their poop, although they're surprisingly fond of getting their poop on other birds or humans (my grey targets me--never does it to my wife, of whom she's jealous.
4. There are significant variations between individual birds, various species,health and possibly even "pecking order" in the flock.

Note: If you own a pet bird, cleanliness of the bird and the bird's environment is very important. In this discussion, I've mixed a combination of wild behaviors with what parrots often instinctively do in captivity. Poop does provide healthy bacteria, but it can also provide a vector for diseases. Except for rare cases like treatment with powerful antibiotics or hand-feeding from day 1, keep all dirt to a minimum to keep your parrot and you healthy.

Our two African greys don't seem to like regular TV. They may need HD, too.

The cockatoo loves TV. He will watch Barney the dinosaur until my eyes and ears bleed, and hates raptors on Animal Planet. Strangely, he likes Corwin Presents, except for that episode with the anaconda.

He hates the weather channel, too, but he was rescued Hurricane Andrew. Not a fan of big winds.

Parrots can engage in corporophagia--they eat parrot poop. If they didn't digest the food completely the first time, they'll get it the second. Their guts are short so their food has a short residence time. The things you do for flight!

It's also how they spread good intestinal bacteria among the flock. If we are forced to hand-feed a parrot chick from day one, we mix some of the mother's feces in the formula for the first week or so. Survival rate improves dramatically, although feeding a bird the size of your little fingernail is still iffy (parakeets and bourkes).

If the recent information on termites is correct, sharing feces may be one strategy for forming societies.

Finally, if you really want to get freaked out, read about treating intestinal infections with feces transplants.

In the 1940s, 61 Cygni was thought to have planets a planet -- then several planets, then none, and now, at least one.It's another example of science correcting itself more than once!