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 even the largest dinosaur, a leviathan that is rarely seen except when it comes up for air and a minute part of its 110-foot-long body breaks the surface and slowly crests for what seems like an eternity. 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. 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 epic migrations to track the historical abundances of krill—the tiny crustaceans that they eat. Rather than finding where their prey 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 astray?
Countless species of animals migrate over long distances to exploit far-flung sources of sustenance, 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, although since the latter are tracking salmon, they’re more accurately “riding the crimson tide.”