Harbor Seals Size up Their Prey Using Whiskers

Seals are cute, furry and now share something else in common with cats--they can judge size by using their whiskers. Known for their touch-sensitive whiskers, seals can use this unusual adaptation to size up their prey.

The findings, published in the Journal of Comparative Physiology A, examined the whiskers of two harbor seals, named Marco and Moe, at the marine science center at the University of Rostock in Germany. Although many species use whiskers as touch sensors, researchers wanted to see the way in which seals specifically use this adaptation. Although mice and rats move their whiskers around in order to get more information about their environment, head researcher Robyn Grant believed that since this technique would cause seals to expend a lot of energy and that they must use a different method.

In order to test the seals, researchers fitted eyemasks and headphones on the seals in order to restrict their other senses. They then taught the seals to choose between two disks--one smaller than the other--in order to receive a fish reward. Moe was supposed to choose the larger disk, while Marco was supposed to choose the smaller disk. In order to examine exactly how they chose, Grant filmed the interactions.

The researchers found that the seals oriented their muzzles to an area where the whiskers are small and densely packed. These whiskers then allowed the seals to gather lots of information from one spot without moving the other whiskers. By feeling exactly how many whiskers the object contacted, the seals were able to figure out approximately how big an object was.

Since seals often hunt in water where visibility is poor, this technique could allow them to better gauge the size of their prey. In addition, it allows them to more quickly analyze their surroundings without expending extra energy--all decisions that the seals made were done in under half a second.

Moving forward, Grant believes that comparative tests in humans could examine which method of measuring size was faster.