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Calculating crows know how to wait

A crow looking off to the left

You gotta know when to hold em: Some crows waited for several minutes before making a decision (Source: Claudia Wascher /)

Holding on New research suggests crows and raven birds rival the ability of monkeys to complete delayed exchange tasks, waiting up to five minutes to swap food for better rewards.

"The results are surprising because we knew that the birds would probably be able to wait for few seconds, but not for so long and not in such a flexible manner," says Dr Valérie Dufour, researcher in ethology and cognition at Université de Strasbourg and study lead author. "Some waited for minutes, which is comparable to what monkeys did."

In humans, deferred gratification has been linked to academic achievement. During the famous Stanford marshmallow experiment, researchers gave four-year-olds a single marshmallow and promised another if they could wait without eating it. Those that went the distance grew up to be more academically and socially competent teens.

Like humans, crows and ravens are social creatures with large brains for their body size. Before the experiment, twelve birds were trained to swap tokens for food, but could they play the waiting game?

Playing the waiting game

Scientists gave each bird a piece of food, and then kept their giving hand closed while showing an exchange reward in the other hand. After the waiting period finished, they opened the giving hand. If the bird returned the initial piece of food, it received the reward in exchange.

Rewards ranged in quality, and birds exchanged more often for high quality foods. The maximum waiting period was five minutes.

During the wait, some birds put the original item on the ground or hid it in a cache, checking on it regularly. "The birds who succeeded at the longest delay all used these distractive tactics while waiting," says Dufour. "Controlling their impulse to eat certainly appeared costly for them."

Professor Gisela Kaplan, an animal behaviour researcher at the University of New England who was not involved in the study, says some Australian bird species may be capable of similar behaviour.

"There have been no experiments of this kind in Australia," says Kaplan, "but Australian ravens cache their food and so do magpies. If tested in a similar experiment, they might also show an ability to wait for the better reward."

"Planning for the future is something not only humans and great apes do, but also some bird species too," she says.

The study appears today in the journal Royal Society Biology Letters.

Tags: animals, animal-behaviour, birds