Pinnipeds orient and control their whiskers: a study on Pacific walrus, California sea lion and Harbor seal
Whisker touch is an active sensory system. Previous studies in Pinnipeds have adopted relatively stationary tasks to judge tactile sensitivity, which may not accurately promote natural whisker movements and behaviours. This study developed a novel feeding task, termed fish sweeping to encourage whisker movements. Head and whisker movements were tracked from video footage in Harbor seal ( Phoca vitulina ), California sea lion ( Zalophus californianus ) and Pacific walrus ( Odobenus rosmarus divergens ). All species oriented their head towards the moving fish target and moved their whiskers during the task. Some species also engaged in whisker control behaviours, including head-turning asymmetry in the Pacific walrus, and contact-induced asymmetry in the Pacific walrus and California sea lion: behaviours that have only previously been observed in terrestrial mammals. This study confirms that Pinnipeds should be thought of as whisker specialists, and that whisker control (movement and positioning) is an important aspect of touch sensing in these animals, especially in sea lions and walruses. That the California sea lion controls whisker movement in relation to an object, and also had large values of whisker amplitude, spread and asymmetry, suggests that California sea lions are a promising model with which to further explore active touch sensing.