Seals Use Whiskers to Judge Object Size

Seals use their whiskers to judge the size of an object, suggests a new study.

It is known that mammals like rats and shrews use their whiskers to explore their environment and determine various object properties such as size, shape and texture. This new study sheds light on how these animals use whiskers as a "sixth sense".

For their study, researchers from Manchester Metropolitan University, U.K., examined the whiskers of two harbour seals named Marco and Moe. The research team wanted to find out how the seals used their whiskers to gauge the size of an object.

The seals were fitted with ear masks and headphones so as to restrict their other senses. They were trained to take part in an experiment where they had to sense two different size discs using their whiskers. The seals were given a fish reward if they identified the correct object - the larger disc for Moe and the smaller disc for Marco, reports BBC.

The researchers filmed the interactions in order to find out how the seals determine an object's size. They observed that the seals press their whiskers to objects and "feel" the size of the objects using the number of whisker contact points. This brushing technique helps seals to gauge the size of an object instantaneously by taking less than 0.4 seconds to decide whether to chase the prey or leave it.  

"What was not known was whether it was the number of whiskers or the way the whiskers were positioned which helped them determine size," Dr. Robyn Grant, a lecturer in environmental physiology at Manchester Metropolitan University, said in a statement.

"The way they oriented their smaller, most rostral, ventral whiskers to the discs suggest it is the former," she said.

The findings of the study are published in the Journal of Comparative Physiology A.