Ian,

I have personally seen a Prothonatary Warbler eat a few tent caterpillars. But other than that I have never seen any other bird even look at them. I asked Kenn Kaufman, when he was out here talking about his butterfly book, if he knew why birds didn't like tent caterpillars. He surmised that they don't appreciate all the webbing that protects them.
I visit Iowa periodically and once in early summer as I drove in I realized that there was quite an investation of tent caterpillars and that was the only year that I got to see both the Black-billed and Yellow-billed Cuckoo.
I would assume that the nomadic nature of tent caterpillars would work well with the cuckoos sometimes parasitizing nests of other species. Drop your eggs and go to where the caterpillars are.

Jim Rosso
Arlington, Va
jlrosso at aol.com