Fig. 11.

Grammar (rewrite rules) for approximating the sequence of acoustic units produced by Eastern Pacific blue whales Balaenoptera musculus. There are three acoustic units, a, b, and d (Oleson et al., 2007), and the sequence begins with a start symbol S. Individual b or d calls may be produced, or song, which consists of repeated sequences of an a call followed by one or more b calls. The symbol | indicates a choice, and ε, the empty string, indicates that the rule is no longer used. A derivation is shown for the song abbab. Underlined variables indicate those to be replaced. Grammar produced with contributions from Ana Širović (Scripps Institution of Oceanography).