In years past, the oak tree in our yard was almost completely defoliated several years in a row by caterpillars. We were considering cutting it down because it was becoming very stressed and we thought it would die. Then I started feeding birds, and having chickadees, sparrows, nuthatches, and woodpeckers like this, even Blue Jays, attracted to my yard saved the tree. I've seen them all in the oak plucking caterpillars, and the tree has thrived because of them.