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Niche construction drives social dependence in hermit crabs

air rushed out through the catheter. Air pressure could not drive the phonic lips and no sound could be produced [6]. One set of phonic lips sits atop each nasal cavity [7]. Passing pressurized air from the nasal cavities through phonic lips causes vibrations in the lips resulting in sounds including echolocation clicks, pulse bursts and fast vibrations called whistles [8]. After recording several epochs of speech-like sounds, we decided to put the behavior on signal. After a trainer’s signal the whale was rewarded for making the speechlike sounds. This allowed us to study the mechanism of speechlike sound production. The whale accepted pressure catheters [6] into his vestibular sacs above and into the nasal cavity below the phonic lips [7]. With catheters in place, the whale was signaled to ‘speak’. Pressure increases preceded each vocal episode. As each vocal burst ended pressure fell (see Supplemental Figure S1). Pressure increases in the nasal cavities ranged from 200 to 500 mmHg; pressure in the vestibular sacs was under 200 mmHg. Harmonic intervals indicated that the humanoid sounds resulted from modulation of a pulse rate [9]. Helium breathing experiments have shown that dolphin sounds are produced by pulse rate variation [8]. Because of the similarity of nasal and phonic lip structure between white whales and dolphins [7], we conclude the same mechanism applies. Our whale mimicked human sounds by varying his nasal tract pressure and making concurrent muscular adjustments of the vibrating phonic lips while over-inflating vestibular sacs. The speech-like behavior subsided after about four years. After the whale matured, we no longer heard speech-like sounds. However, NOC remained quite vocal. He produced typical echolocation pulses with peak frequencies between 60 and 120 kHz, whistles with fundamental frequencies of 2 to 10 kHz and various pulse burst sounds previously described as “squawks, rasps, yelps or barks” [4]. Vocalizations reminiscent of human speech have been observed for white whales in the wild [3]. The human brain is quick to recognize words [10]. Even partial or garbled words are identified. Reports of animal mimicry based solely on hearing vocalizations must be viewed skeptically. We do not claim that our whale was a good mimic compared to such well-known mimics as parrots or mynah birds. However, the sonic behavior we observed is an example of vocal learning [5] by the white whale. It seems likely that NOC’s close association with humans played a role in how often he employed his human voice, as well as in its quality.