If someone could pull this off, it would be amazing. Cigarette filters probably contain no nutrition though, so you know what will happen to all the butts, eventually. It will come out of their butts ...

Sounds good except the compounds in cigs that make it bad for humans are deadly for birds and small children. I am surprized the ecologists have not picked up on this and used it as a weapon against the tobacco companies. The amount of nicotine that is concentrated in a butt is enough to make a small child violently ill if not kill them. The "medicine" used to kill mites in birds is concentrated nicotine that you put on their roosts in a fine line of liquid and the "fumes" from it kill the mites.

What if the pigeons were hooked on nicotine? Then they'd want the butts. However, they wouldn't eat the filters. Could those be made from some edible plant substance, perhaps something that pigeons would enjoy?

hmm

Once the pigeons are addicted to nicotine, and all the cigarette ends have been cleared up, what do you think they'll do? Go out and buy patches?

I think not. They will snatch the burning cigs out of the mouths of the smokers on the street.