Cold call: the acoustic repertoire of Ross Sea killer whales (Orcinus orca, Type C) in McMurdo Sound, Antarctica

Killer whales (Orcinus orca) are top marine predators occurring globally.
In Antarctic waters, five ecotypes have been described, with Type C being
the smallest form of killer whale known. Acoustic recordings of nine
encounters of Type C killer whales were collected in 2012 and 2013 in
McMurdo Sound, Ross Sea. In a combined 3.5 hours of recordings, 6386
killer whale vocalisations were detected and graded based on their
signal-to-noise ratio. Spectrograms of the highest-quality calls were
examined for characteristic patterns yielding a catalogue of 28 call types
(comprising 1250 calls). Acoustic parameters of each call were measured
and summarised by call type. Type C killer whales produced complex calls,
consisting of multiple frequency-modulated, amplitude-modulated and pulsed
components. Often, two components occurred simultaneously, forming a
biphonation; although the biphonic components did not necessarily start
and end together, with one component lasting over several others. Addition
and deletion of components yielded call subtypes. Call complexity appears
stable over time and may be related to feeding ecology. Characterization
of the Type C acoustic repertoire is an important step for the development
of passive acoustic monitoring of the diverse assemblage of killer whale
ecotypes in Antarctica’s rapidly changing marine ecosystems.