Seals judge size using their whiskers

Harbour seal whiskers Seals measure size with their short front whiskers

Related Stories

Seals are able to judge the size of an object using their whiskers, according to research.

The mammals are known for their touch-sensitive whiskers but scientists wanted to know exactly how they size up their prey.

Researchers from Manchester Metropolitan University found that the animals move specialised whiskers towards an object to measure it.

The results also showed how quickly seals could judge size.

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

Dr Robyn Grant travelled to the marine science centre at the University of Rostock in Germany to study the whiskers of two harbour seals named Marco and Moe.

Recent hydrodynamic research showed how seals can size up fish based on the wake they leave as they move through the water.

Seal secrets

Seal under water

Meet the seals that call the island of Orkney home

Watch how a seal finds a toy submarine in the dark

Why are seals around the Essex estuary a rusty colour?

"We thought it would be good to do more of an in-depth study to look at how they do it rather than just whether they can do it or not," explained Dr Grant.

Many species use whiskers as touch sensors and animals such as rats and mice move their whiskers around in order to get more information about their environment.

For seals, however, this would require a lot of energy expenditure, according to Dr Grant, because water is denser than air and takes more effort to move through.

"I thought they would probably do something more like humans," she told BBC Nature. "Humans detect size by calculating the span of their fingers."

But instead of using their whiskers in the same way as we use our fingers, the seals showed a specialised approach.

Wearing eyemasks and headphones to restrict their other senses, the seals were trained to take part in an experiment in which they had to sense two different size discs using just their whiskers.

To test whether they could tell the difference in size, the seals had to touch their nose to the correct object - the larger disc for Moe and the smaller disc for Marco - for a fish reward.

Dr Robyn Grant places headphones on a seal Dr Grant worked with trained seals

Dr Grant and colleagues filmed the interactions to understand precisely what was happening.

"They orientate to this special place on their muzzle which is where the whiskers are really small and really densely packed," said Dr Grant.

She explained that these whiskers acted as a "higher-resolution sampling space", meaning that the seals could gather lots of information from one spot without moving all of their whiskers.

"They can press [their muzzle] on [the object] and by the number of whiskers it contacts, they can work out whether it's a bigger or smaller thing."

This brushing technique allows the seals to gauge their prey in water where visibility is often poor.

Dr Grant suggested that it might also be a quicker way to work out the size of an object because it did not require more complicated span calculations.

"We've found that they do it super-quick - all their decisions are made in under half a second," she said.

The biologist proposed that comparative tests in humans might examine which method of measuring size was faster.

Join BBC Nature on Facebook and Twitter @BBCNature.

More on This Story

Related Stories

The BBC is not responsible for the content of external Internet sites

More from nature

  • Cardinal fish and ostracodFish filmed spitting 'fireworks'

    Film crew captures ostracods' spectacular defensive lightshow that makes predatory fish spit them out.

  • Arapaima'Locally extinct'

    A giant fish which used to dominate the Amazon river is now absent in many areas

  • DragonflyRapid reactions

    Dragonfly's super quick reactions recorded in slow motion by BBC film-makers

  • Wingless adult male of the midge Belgica antarcticaExtreme survivor

    Antarctic midge's small genome may be an adaptation to its extreme environment

  • Myotis midastactus specimen (previously identified as Myotis simus)Golden discovery

    A bat from Bolivia is described as a new species by scientists

  • Dinosaurs 'shrank' to become birds

    Huge meat-eating, land-living dinosaurs evolved into birds by constantly shrinking for over 50 million years, new research shows.

  • Would we starve without bees?

    Honey bees are under threat, and as pollination significantly contributes to the food we eat, what would we do without them?

  • Eggshells may act like 'sunblock'

    Birds' eggs show adaptations in pigment concentration and thickness to allow the right amount of sun for embryos, scientists say.

  • Female shrimps are more aggressive

    Female snapping shrimps are more aggressive than males when defending their territories despite their smaller claw size, a study shows.

BBC iWonder

  • Honey bee close-upInsect intelligence

    Are honey bees as smart as your sat nav?

  • Tyrannosaurus rex skull (c) Mark Williamson / Science Photo LibraryDinosaur dynasty

    One group of dinosaurs survived and their descendants can be seen all around us today

  • Brown rat cluse upRise of the rodent

    Reports of giant, 'super rats' are filling the headlines. But why are we being overrun by rats?

  • Cuckoo portraitHoliday hotspot

    What makes the UK such an attractive destination for visiting wildlife?

There have been 75 solar eclipses and 167 major volcanic eruptions in my lifetime

Nicole Malliotakis on Twitter comments on the events that have happened since she was born by using our personalised Your Life on Earth interactive infographic.

Get Inspired


More Nature Activities >

Copyright © 2015 BBC. The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.