Imagine trying to test the memory of the blue whale—the biggest animal that exists or has ever existed, a 190-ton behemoth that dwarfs (使相形见绌) even the largest dinosaur, a leviathan that is rarely seen except when it comes up for air. How would you subject such a creature to a psychological test?
You can’t, exactly. But there is another way to get a sense of how their minds work. For years, scientists have been fitting radio tags to these giants to track their whereabouts (下落). By analyzing a decade’s worth of that data, Briana Abrahms from the National Oceanic and Atmospheric Administration has shown that these animals fine-tune the paths of their migrations to track the historical abundances of krill—the tiny crustaceans that they eat. Rather than finding where their prey (捕获物) currently is, they go after the places where their prey was in years past. Their migrations, in other words, are guided by memory. So what happens in a world where memory might lead them away from the right path?
Countless species of animals migrate over long distances to exploit far-flung sources of food, but these voyages aren’t just about getting to the final destination. The journey itself can be a sort of food tour, too. Migrating animals often adjust the pace and timing of their movements to hit pulses of seasonal food that spring up along their path. The ecologist Sandra van der Graaf described this as “surfing the green wave” after first observing it among barnacle geese. Others have found the same pattern among wasps, elk, mule deer, and brown bears.”
The blue whales of the North Pacific spend their winters in their breeding grounds off California and Costa Rica. Come spring, they swim up the coast of North America toward the food-rich summer waters of the Pacific Northwest. They could make the journey in two months (and they do, on the reverse trip back south). Instead, they take twice that time, pausing to gorge (狼吞虎咽) themselves on blooms of krill that appear along the way. It’s a leisurely season-long tour of a continent-wide buffet line.
Scientists can get a good sense of this changing buffet by measuring the concentrations of chlorophyll in different patches of ocean. This green pigment (色素) reflects the amount of plankton, which in turn is eaten by krill. The more chlorophyll there is, the more food a blue whale might find.
By comparing chlorophyll counts to whale movements, Abrahms and her team expected to see that “they follow the timing of their prey, as it becomes available,” she says. But they were surprised to learn that the animals very rarely tracked contemporary waves of krill. Instead, their movements were strongly correlated (相关联) with 10-year historical averages of chlorophyll. Put it this way: You could predict a blue whale’s movements with far more accuracy by looking at where their food has been than where their food currently is.
【小题1】How are the scientists carrying out a psychological test on the blue whales?| A．They wait for the blue whales to approach the sea surface. |
| B．They induce the blue whales to accept the memory test. |
| C．They count on a tracking technique to accumulate data. |
| D．They compare the blue whales with the large dinosaurs. |
| A．They might try their best to get to the final destination. |
| B．They might fall back on the seasonal food along the way. |
| C．They might accelerate the pace to cover longer distances. |
| D．They might surf the ocean wave to save time and energy. |
| A．The breeding grounds of the blue whales are lacking in food. |
| B．Chlorophyll can be defined as the beginning of the food chain. |
| C．Contemporary waves of krill can reflect whale movements. |
| D．The season change determines the hunting route of the whales. |
