Any time we have heavy rain (i.e. all the time), any paved areas will become littered with the corpses of drowned earthworms. I would have thought that an easy source of protein such as this would be eagerly exploited by birds and other wildlife, but nothing seems to bother touching them; they sty where they are until they rot or dry up into earthworm jerky.
Why don’t birds eat dead earthworms?
I have seen ants carrying off worm carcasses (chanting “Oh we oh, yoooo ho!”) after rains.
Recently on a tomato-growing forum I heard speculation that tomatoes don’t taste as good after heavy rains, because the flavor components are diluted. Maybe the birds feel that way about earthworms.
Dunno… I don’t think birds have a very developed sense of taste (in a physical, not aesthetic sense, I mean). Thing is, it’s winter and food for wild birds is otherwise scarce, yet they’re not touching it.
I think these worms are infested with parasites or microbes. If so, this might affect how they taste to birds, or might even be infectious. As a result, our feathered friends have probably learned to avoid these noxious corpses.
For as B.F. Skinner said: “Don’t let nobody kid youse. Them birds are fuckin’ smart.”
Until someone figures a way to ask the birds, there may not be a definitive answer to this question.
Perhaps the thing that attracts birds to earthworms is the movement, so if they are still there is no interest?
I did some digging around (geddit!) and found this that seems to support the theory:
"Dr. Heppner considered ALL the senses that a robin might use to find worms.
TASTE: NOPE!! Robins would have to taste a LOT of dirt to pick out worms this way!
SMELL: Dr. Heppner recorded that “robins nonchalantly ate foods smelling like rotten eggs, decaying meats, rancid butter, and the absolutely worst smell of all bad smells, mercaptoacetic acid.” So they don’t seem to notice that nice wormy smell at all!
TOUCH: If robins feel vibrations of live, wiggly worms, they wouldn’t bother eating still, dead worms. But when Dr. Heppner drilled worm-like holes in the ground and placed dead worms in them, the robins found and ate them readily!"
From here: http://www.learner.org/jnorth/spring1999/species/robin/Update051899.html
Your cite actually appears not to support that notion, suggesting instead that it’s a matter of proper location of the foodstuff.
I guess what I was trying to prove was that if worms are lying on paths, prone, they will be ignored. If they are moving they will be eaten. If they are prone in a place where birds know they will find them, they will be eaten.
Therefore, birds will eat dead earthworms, but only if they already have a sense of where they are.
Of course, now you’ve said it, I can also see that moving or not could be irrelevant, and other sense factors are more important. Hey ho!
Because eating a dead worm would be icky.
Oh, and eating a live one is. . . .what? 
Whooshy.
Many predators won’t eat dead animals (carrion), because the animal may have died of a contagious disease, or because the corpse may have been sitting there long enough to attract bacteria, parasites, and other nasty things you don’t want to consume in bulk unless your digestive system has been specifically adapted to deal with it. (Many prey animals, such as opossums, use this fact to their advantage by playing dead when faced with danger. Statistically speaking, they have a better chance at survival by assuming the predator in question won’t eat carrion than by attempting to run away or fight back.)
It could be that the birds which normally feed on worms are precisely the kind of predators which avoid carrion. Why risk an upset stomach, or worse yet, disease, by eating a dead worm found on the sidewalk when you can get a fresh worm from the ground?
Maybe the birds do eat the dead earthworms but fill up quickly and ignore all of the ones that we see.
I’m with you, Bubba.
In addition, many animals have a tendency to eat only live things, not carrion, unless desperate, and sometimes not even then.
Paging Colibri…