A harbor seal (Phoca vitulina) shows extensive respiratory control in sound production.

The duration of animal vocalizations varies between and within species. Which mammals can learn to control this duration? Such respiratory production learning is a scarcely studied subcomponent of vocal learning. Here, we test the hypothesis that harbor seals (Phoca vitulina) are capable of respiratory production learning by testing whether a harbor seal can be trained to i) actively control its vocalization’s duration in two directions (short and long), and ii) exceed the pre-experimental vocalization’s duration (min = 0.202 s, max = 2.621 s). The seal learned to produce uninterrupted vocalizations spanning more than two orders of magnitude in duration, from 79 ms to 9.23 s. Our findings demonstrate a remarkable level of respiratory control in a harbor seal: this respiratory production learning encompasses an extensive range of sound durations and arises at a young age. Producing durations that span such a magnitude is hardly reported in the non-human animal literature; this capacity may be orthogonal to other vocal learning modules and should be tested in more species, both vocal production learners and non-learners.