Welcome to ATP!
Unfortunately, I can't find any reference to birds dining on this particular caterpillar. These guys are unique in that they tend to feed side by side in a group and, when disturbed, raise their heads or rears in unison. They are also most active in August and September. It is believed that they only lay eggs once per year in the spring (80-100 eggs on the back of a leaf) so there is only one generation produced annually. Handpicking is an effective treatment (as is Bt and the standard pesticides) but you may want to toss them in a bin next time. In addition to azaleas, they are also known to chew on red oaks, blueberry bushes, and the occasional apple tree. Again,
to ATP. Perhaps someone else knows if birds will eat them.