More than song and calls: New repetitive tones for humpback whales in the breeding area of Colombia

The vocal repertoire of humpback whales (Megaptera novaeangliae) consist of long and complex songs and social calls. Songs are characterized by their cyclical and predictable structure in form of units, phrases, and themes. On the contrary, social calls are less predictable and generally short bursts of vocalizations that mainly occur during inter or intragroup interactions. During monitoring activities of reproductive stock G in Bahia Solano (Breeding ground, Colombia), a series of undescribed vocalizations were recorded, which we called repetitive tones. These are loud, frequency modulated (between 280 and 770 Hz), quickly repeated vocalizations. They are shorter than one second and have short inter-call intervals (from 0.7 to 1.0s). They do not follow the pattern of either vocal category established in the species' repertoire. Here we discuss the occurrence of such vocalizations as a result of acoustic and behavioral plasticity of cetaceans. We explore vocal mimicry, song crystallization, or the documentation of a new single-unit song type as possible scenarios to understand the potential function(s) of these tones. Framing acoustic behavior in the cognitive and adaptive capacity of cetaceans argues for a third vocal repertoire category that could serve as the basis for contextualizing new behavioral displays.