“…Early research into vocal control and flexibility in mammals was investigated using operant techniques in dogs (Salzinger & Waller, 1962), cats (Molliver, 1963), and rats (Lal, 1967). Studies on primate vocal behavior often made use of operant conditioning (Leander, Milan, Jasper, & Heaton, 1972; Pierce, 1985; Sinnott, Stebbins, & Moody, 1975). Pinniped vocalizations too have been studied in depth, which is particularly interesting because they are among the few clades of mammals considered vocal learners.…”