Body contact and synchronous diving in long-finned pilot whales.

Synchronous behavior, as a form of social interaction, has been widely reported for odontocete cetaceans observed at the sea surface. However, few studies have quantified synchronous behavior underwater. Using data from an animal-borne data recorder and camera, we described how a pair of deep-diving odontocetes, long-finned pilot whales, coordinated diving behavior. Diving data during overlapping periods of 3.7 h were obtained from two whales within a stable trio. The tagged whales made highly synchronous movements, and their dive durations differed only slightly (3±3 s). The pair of whales maintained a constant and narrow vertical separation (ca. 3 m) throughout synchronous dives. The overall fluking rate for the same travel speed during synchronous dives was virtually the same as that during asynchronous dives, suggesting that synchronous behavior did not affect locomotion effort. In addition, a possible affiliative behavior was recorded by the animal-borne camera: another individual appeared in 8% of the frames, both with and without body contact to the tagged whale. The primary type of body contact was flipper-to-body. Our study, the first on underwater synchronous behavior and body contact of pilot whales, highlights the utility of using animal-borne devices for enabling new insights into social interactions.