open call system
a system of vocal communication in which new vocalizations can be added throughout life. Whereas many songbirds rarely show change in song structure after the end of a critical period, other birds, including parrots, starlings, mynahs, and mockingbirds, can acquire new calls and songs throughout their lives. Few mammals have an open call system, but some dolphins and whales show evidence of acquiring new calls throughout life. Compare closed call system.