Some animals in the world have a natural ability that human beings don't have.
Seals may be able to detect (探测) fish up to 100 m away using only their whiskers (胡须), say scientists. Researchers used an artificial(人造的) fish in their experiment, to create a "trail" in the water that a seal could detect. They described how a trained seal, named Henry, was able to indicate(显示), with a rapid movement of its head, whether the fish moved to the right or to the left.
The study was led by Wolf Hankie of the Marine Science Center at the University of Rostock, Germany. He explained how the seal wore a blindfold (眼罩) and headphones during the experiment to ensure that it could only pick up waves created by the fish with its whiskers. "The animals are actually enthusiastic to wear the mask because it means play time and food rewards," explained Dr. Hankie.
"We had a small box in the pool to achieve calm water conditions," he explained. "The seal stayed in the box. " Inside the box, the scientists created a trail with their artificial fish, which was actually a rubber fin (鳍) on a stick that created a trail similar to the swimming motion(运动) of a real fish. They operated the fin from outside the box, moving it from left to right or from right to left. The seal responded to the movement by turning its head in the direction that the fin had moved. The seal was able to sense and indicate the direction in which the fin travelled up to 35 seconds after the movement had stopped.
Dr. Hankie believes that seals may also be able to "analyze" the structure of a trail to "work out" more about its source. He and his colleagues (同事) used different shapes of fin to create different water disturbances. "They seem to be able to detect differences between different shapes, which might even mean that they can make out different species of fish. We had a surprising result from an experiment with one seal following another," he said. "The trail left by the first seal was two meters wide, and the second following seal was able to stay right in the middle of it, so it seems they can analyze the internal structure of a trail."
The researchers are now making experiments using live fish to see how closely seals are able to follow their moving path.
