Crows Understand Caw-se and Effect

New Caledonian crows put their intelligence on display, again.

In Aesop's fable "The Crow and the Pitcher," a parched crow discovers a pitcher holding water. The liquid is pooled at the bottom of the vessel where the crow can't reach it. So in typical Aesopian fashion, the crow comes up with the idea to drop pebbles into the water one by one, making the liquid rise to the top and allowing the bird to quench its thirst. The moral of the story: "Little by little does the trick."

Scientists from New Zealand recently brought the fable to life. They put New Caledonian crows to the test with vessels of various shapes and sizes. In most instances, crows were able to manipulate the water level to a height that allowed them to reach a morsel of food that was floating on top, they report this week in PLOS One. The same task—known as the Aesop's fable paradigm—has been given to children as a cognitive test.

Sarah Jelbert, a PhD student in psychology at Auckland University and the study's lead scientist, wanted to test out the limits to the crows' understanding. So she and her team trained six wild New Caledonian crows to drop stones into tubes.

They then placed the birds in six different scenarios—all of which required dumping objects into water, or sand in one case, to reach the floating food (check out the video below).

The birds, it turns out, performed about as well as an 8-year-old child. Jelbert believes that the birds understood the cause-and-effect relationship between putting the stone in the water and having the liquid rise: They seemed to realize that heavy/solid objects sink and light/hollow objects float. They had the most trouble with a U-shaped tube, probably because it didn't follow the typical cause-and-effect rules. Jelbert doesn't think that age, sex, or familiarity with the task factored into their success.

And lest anyone think there's a direct comparison between kids and crows, Jelbert emphasizes that the analogy was made simply to show that solving these problems requires a great deal of brain power. "We don't know whether crows are solving the tasks in the same way as children," she says.

Whatever the case, there's no arguing that New Caledonian crows are clever. In 1996, another researcher from New Zealand, Gavin Hunt, found that the birds can make and use their own tools. Jelbert's study digs deeper into the cognitive abilities of crows. "By studying the New Caledonian crows and investigating the emergence of intelligence in a distantly related species, we can try to find out whether intelligence evolves in predictable ways," says Jelbert, whose work is supported by the Royal Society of New Zealand.

As for Aesop, it seems that he was both a great storyteller and a psychic, at least in this case.

[video:209101|caption:This is footage from all six experiments, as provided by Sarah Jelbert and edited by New Scientist.]