"Birds are often associated with cosmic or world trees. In Maya art, these birds are usually the "principal bird deity." At Yaxchilan, this deity does not appear, and the birds represented resemble those appearing in Bird Jaguar's name and the bird-and-flower headdresses. They may be a way of specifying this cosmic tree symbol as a local one."
Carolyn E. Tate, Yaxchilan: The Design of a Maya Ceremonial City, p. 68