Sources : Titmouse

Pliny the Elder [1st century CE] (Natural History, Book 10, 50; 10, 95): [Book 10, 50] There is a species of titmouse that makes its nest of dry moss finished off in such a perfect ball that its entrance cannot be found. [Book 10, 95] ...that very tiny bird the titmouse [fights] with the ass, which by rubbing itself against thorns for the sake of scratching dislodges the nests of the titmouse [aegithus], which is so scared that when it merely hears the sound of an ass braying it throws its eggs out of the nest, and the chicks themselves in fear fall out, and consequently the bird flies at the ass and hollows out its sores with its beak. - [Rackham translation]

Thomas of Cantimpré [circa 1200-1272 CE] (Liber de natura rerum, Birds 5.43): Echitus, as Pliny says, is the smallest bird, which has enmity with the ass. For the ass, scratching itself with thorns, destroys the bird's nests, which frightens the bird so much that, hearing the braying of the ass, it immediately flies from the nest, and its chicks fall from it in fear. But sometimes she vindicates herself. For by flying she digs the sores of the ass with her beak and does not stop, although it flees. - [Badke translation/paraphrase]