In an animal communication studies of capuchin monkeys, the "duck face" term has been used synonymously with "protruded lip face", which females exhibit in the proceptive phase before mating.
Dalam studi komunikasi hewan monyet capuchin, istilah "wajah bebek" telah digunakan secara sinonim dengan "muka bibir menonjol", yang ditunjukkan oleh betina dalam fase proseptif (fase awal) sebelum kawin.