Giving seals a second chance

Richard Collins examines seals and what they can teach us about the tides and the passage of time.

Mon, 02 Jan, 2017 - 00:00

At the start of a new year, one’s thoughts turn to time. As we age, years appear to pass as quickly as weeks did when we were children.

If your watch has a ‘second’ hand, try memorising how long a minute seems. Then, without looking at the watch, estimate the passage of another minute. Resist the temptation to listen to your heartbeat or count seconds in your head. According to a paper in Animal Cognition, seals can measure short intervals more accurately than we can and they don’t need a Rolex to do so.

Luca is a trained harbour seal at the University of Rostock’s Marine Science Centre in Germany. Researchers showed him the image of a white circle against a black background on a computer monitor. The display was switched on and off for intervals of three to 30 seconds. Luca had to decide whether an exposure was of the same duration as the one preceding it. When he judged that the periods were equal, he pressed a button. If he thought that an exposure was longer, he pressed a different one. Correct choices were rewarded with handouts of fish.

The researchers found that Luca was able to discriminate between intervals differing by 420 milliseconds. To equal his performance in our crude experiment, you would have to estimate the length of minute to within a second. A minute is a long time in a mouse’s world. How long is it in a seal’s? Our experiment, therefore, may not be entirely valid.

Physicists claim that there are 11 dimensions but we experience the world in just four; three spatial ones and time. How wild creatures use space has been extensively researched; territory sizes, home ranges, and the distances travelled by migrating birds, are well documented. The fourth dimension, time, has received much less attention.

Starlings, in ‘murmurations’ a million strong, need the timing skills of ballet dancers and trapeze artists to avoid catastrophe. A peregrine may ‘stoop’ on a pigeon at 300kph. Baby turtles, deep in the burrows where they hatch, usually know when it’s dark at the surface, time to dig their way out of the sand and scamper down to the sea. Light can’t penetrate the ground, so how do the hatchlings know when to move? Does a biological alarm clock alert the baby that it’s time for the crucial dash?

A turtle’s hard-wired timer would, presumably, be used only at the start of life. Some animals, however, have more flexible mechanisms; dogs, it’s claimed, can sometimes predict when their owner will arrive home in the evening. Natural selection has equipped each creature with the skills it needs, but why do seals require precision time-keeping?

The ‘harbour’ seal is a familiar Irish resident. It used to be more abundant than its larger ‘grey’ cousin but, despite the alternative name, it’s no longer ‘common’. The banana-shaped head-up-tail-up profile is a familiar sight when seals haul-out on the rocks at Glengariff’s Garinish Island. The sandy eastern tip of Dublin’s Bull Island usually has a resident ‘herd’.

It’s easy to tell our two Irish species apart. The grey ‘bulls’ are much larger than their ‘cows’ and have flattish horse-like faces. Harbour seal males are only slightly bigger than females and the ‘noses’ tend to be up-turned like a dog’s. The ‘V’-shaped nostrils are distinctive.

Being able to time the movements of complex currents in tidal harbours and wind-swept estuaries might be a useful skill for a seal to have. Although the common seal is an opportunist feeder, taking crustaceans squid and octopus from the sea-bottom, small to medium-sized fish are its main prey. Like penguins and dolphins, this ambush predator probably evolved timing skills to help it catch elusive prey.