I've fed tent caterpillars to both chickens and ducks with mixed results. No ill effects at all - but these were free-range birds on mixed perennial pasture with plenty of access to other things for their diet - but it seemed like some of the birds just didn't *like* them. About half the ducks went nuts for them like they were gummy worms in a kindergarten
class, the rest of them were sort of "meh" about them. None of the chickens went as crazy as the ducks that loved them, most of the chickens ate a few of them and then moved on to other things. Some of the chickens played with them, but didn't seem to eat many. Some of the chickens totally ignored them after a few cursory pecks.
My flock of 40 birds, 25ish chickens and the balance ducks on free range and fermented grains (fed only at night, day time is for hustling up their own grub!), pretty well decimated two nests a few times a week. More than that and the caterpillars just sort of got trampled into the coop litter...which is maybe not too bad, if you're trying to get rid of the caterpillars more than you're trying to feed the birds. I definitely didn't see any indications that they were poisonous in those amounts, but many species of caterpillar are mildly toxic and it wouldn't surprise me if the range of reactions my birds showed was each of them eating the caterpillars at the rate their bodies could process the toxin and remain undamaged - which would make sense also with nests fed more often being ignored, they knew that they'd already "hit capacity" on that food and consuming more of it would cause problems. Animals have a lot more sense about self-doctoring and self-limiting their intake of "dangerous" things than we give them credit for, especially when they have free access to a wide range of foodstuffs rather than being stuck in a tiny dark barn and only fed grain. An animal with that history could easily overeat on a toxic food, simply through inexperience and desperation.