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Birds infer their partner’s desires during bonding ritual

Then they feed them a worm.

Birds infer their partner's desires during bonding ritual

The corvids, a group of birds that includes crows and jays, display some of the most complex behaviors seen in any birds: tool use, an ability to associate faces with behaviors, and the recognition of when one of their peers has died. In a number of cases, these birds have been seen exhibiting behaviors that, until recently, were thought to be limited to primates. Now, researchers suggest there's another complex behavior we can add to their impressive list: the ability to infer the desires of others.

This behavior was observed in Eurasian jays, a species ranging from Western Europe to India. Pairs of jays engage in courtship behavior that includes the sharing of food, which helps in the formation and maintenance of pair-bonds. Researchers at Cambridge decided to test whether the males could successfully figure out what sort of food their partners might want.

You might think that, to a bird, one meal is as good as any other. But at least for jays, you'd be wrong. The birds actually aim for variety when they make caches of food to eat later, trying to ensure they'll have a mixture of food to enjoy the next day. The researchers confirmed that Eurasian jays have a similar desire for variety. If researchers pre-fed the jays a meal of wax moth larvae (mmm!) and then offered them a mix of that and mealworm larvae (double mmm!), the birds preferentially ate the mealworms. If the researchers did that after a meal of bird food, the birds chose the wax moths at a greater frequency.

When males were given the chance to present foods to their mates, they acted as if the female had just been given bird seed—they gave their mates a mixture of wax moths and mealworms. But if the males had the chance to watch their partners being fed a bunch of wax moths, their gifts shifted, and mealworms were presented with a much higher frequency. This eliminated the possibility that the female somehow signaled the male to indicate which treat she preferred (if that were the case, it wouldn't matter whether the male watched her eat before hand).

The one remaining possibility the researchers considered is that the male ended up feeling satiated with wax worms just by watching the females chow down on them. But the males showed identical feeding behaviors whether they watched their partners eat or not.

The researchers conclude their experiments show these birds are capable of attributing a specific mental state to others (namely, desiring a mealworm). They base this on the fact that the males weren't simply giving the females what they wanted. In other words, their frequency of gift types didn't match the frequency at which they ate. In addition, they note the females didn't provide any signals that the males used to determine what to feed them. With those two possibilities eliminated, the authors conclude that the males were inferring the desires of the females.

The researchers also place this work within the framework of what's called a "theory of mind." Early on in childhood development, kids are able to infer what other humans are likely to want or hope for. By around age four, they can start inferring more complex mental states, like their beliefs or the state of their knowledge. The latter is considered a full-blown theory of mind, in that you can make inferences about the mental state of other people.

There's no evidence birds have a full theory of mind, at least not from these experiments. But it's been argued that the ability to infer desires is a key building block of humanity's ability to form a theory of mind. Based on this work, the birds may have that.

PNAS, 2013. DOI: 10.1073/pnas.1209926110  (About DOIs).

Channel Ars Technica