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Do Tayras Plan for the Future?
5 August 2011 12:34 pm
Humans buy unripe bananas, then leave them on the kitchen counter. The tayra, a relative of the weasel native to Central and South America, appears to do much the same thing, picking unripe plantains and hiding them until they ripen, according to a new study. The authors speculate that tayras are showing a human-like capacity to plan for the future, which has previously been shown only in primates and birds.
Biologist Fernando Soley was an undergraduate at the University of Costa Rica in 2004 when he first started thinking about tayras. He was studying poison dart frogs at La Selva Biological Station in northern Costa Rica, when he noticed a tayra—essentially a giant weasel with a bushy tail—approach a tree. "It climbed 4 meters high, went directly to a bromeliad [a plant growing in the tree], and came back down with a ripe plantain and ate it," Soley says. The trees in the forestry plantation where he was working are planted in neat rows, and it's easy for humans to get lost. Because the animal went straight to the plantain, he thought it couldn't have found it by chance. "I thought, wow, for sure this animal was the one that brought it there."
A few years later, Soley came back for a closer look at the tayras, teaming up with Isaías Alvarado-Díaz, a self-taught biologist who lives near La Selva. Animals don't spend much time in the forestry plantation, so Soley thought tayras might hide their fruit there to keep it safe from prying snouts. The duo set up an Easter egg hunt for fruit thieves to find out if the tayras were doing a good job. "We hid pieces of banana, which pretty much tastes and smells very similar to plantains, in the forest and in the plantation, and after 2 days we went to count them," he says. Animals found fewer bananas in trees than on the ground, and fewer in the plantation than in the forest. That means hiding plantains in the plantation and up in tree is a smart move by tayras that don't want other animals to find their treasures.
Soley and Alvarado-Díaz also monitored plantain plants to see what fruits were being taken. They borrowed motion-sensitive camera traps from a research team that studies mammals and confirmed that tayras were the only plantain eaters that snapped off a whole fruit; toucans, coatis, and opossums gnawed on ripe fruits while they were still attached to the plant. Soley was surprised to find that the tayras were not only eating ripe plantains, but also taking unripe ones. They borrowed radio transmitters, taped them into unripe plantains, and found that the unripe fruits were taken away and eaten later.
Many birds and animals cache food, but most do it with leftovers—food that could be eaten now but isn't needed. Shrews stash extra insects; squirrels hide nuts. Soley says tayras are different because the unripe plantains aren't edible yet. "It's like knowing that it's going to be food in the future," Soley says. That means the tayras are thinking about their hunger a few days from now and planning ahead, he and Alvarado-Díaz report in this month's issue of Naturwissenschaften.
Several studies have found the capacity for forethought in nonhuman primates and some birds, but the results are controversial because some people think only humans can think ahead. Cognitive scientist Mathias Osvath of Lund University in Sweden is confident that, for example, a zoo chimp that he wrote about in one paper plans for the future by calmly collecting rocks and making concrete disks to throw at zoo visitors later, but he says Soley's study doesn't provide conclusive evidence that the tayras are doing so. "One of the signs … is being able to plan for a need that you're currently not experiencing," he says. "For example, we don't know if the tayras are actually hungry when they are caching."
Osvath says more research is needed to tell if the tayras are imagining a hungry future 5 days from now, or if they've just learned that if you leave a fruit and come back a few days later, it will be edible. "True planning is when you shut your eyes and you think about what you will have for lunch tomorrow."