Human Eyes Speak Volumes to Birds
Birders know that birds are geniuses at reading human body language — but how good are they at this?
Those of you who go birding will know what I am talking about when I say that birds are so capable of reading human body language that they know when we are looking at them, which frequently causes them to hide from our gaze. However, this capacity has never before been scientifically studied in birds, until now, that is.
A newly published paper reports on studies of hand-raised, tame Eurasian Jackdaws, Corvus monedula, a small relative of the crows. Jackdaws’ eyes have a dark pupil surrounded by a striking silvery iris — similar to human eyes.
“I think they can generalize to human eyes somehow, and interpret human eyes as eyes,” explained Auguste von Bayern, lead author on the paper, formerly of the University of Cambridge and now located at the University of Oxford.
Because these birds were handfed and were therefore very familiar with people, the researchers believe these birds were even more capable of interpreting human gaze and body language than their wild counterparts.
“Jackdaws seem to recognize the eye’s role in visual perception, or at the very least they are extremely sensitive to the way that human eyes are oriented,” she continued.
To test the birds’ ability to interpret human gaze, ten hand-raised jackdaws were placed into a threatening situation where a preferred food item — the “reward” — was presented to them while in the presence of a human. The threatening situation was the result of being in the presence of a person who was a stranger to the birds and comparing the birds’ reactions with their reactions when in the presence of a person who was familiar to them (figure 1);
These data show that the birds took longer to retrieve the reward when the stranger was looking toward the food item than when they were looking away from it.
To determine the jackdaws’ response to more subtle attentional cues and to control for any potentially unwanted behavioral cues by the human, the team then tested the jackdaws using a series of digital photographs of a different stranger’s face that displayed several attentional states (figure 2);
They found that, independent of the person’s facial orientation in the image, the number of visible eyes, or the perceptual similarity or dissimilarity of the stranger’s attentional states, the time until the birds approach towards the food item depended on whether the human’s eye(s) were oriented toward the food reward.
Because Jackdaws are cooperative species where members of a pair will share actively direct each others’ attention to particular objects, the researchers then tested whether they would respond to a cooperative task with a human partner. To do this, the researchers baited one of two identical opaque chambers with a food reward. To determine if the Jackdaws were reading eye gaze or body language preferentially in a cooperative task, the human partner provided one of four distinct social cues to the birds; either gazing at the baited chamber without turning her head (G) or turning her head towards the baited chamber while gazing at it (G + H), and two body language cues; first where the stranger alternated her gaze repeatedly between the subject and the baited container (GA), or pointing at the baited chamber with her finger (CBP) (figure 3);
According these data, the birds successfully interpreted human communicative gestures, such as gaze alternation and pointing, to help them find hidden food. However, the birds were unsuccessful in using static cues, including eye gaze or head orientation in this experiment.
Their skittish response to strangers may reflect an evolved response to potential predators or other threats, when subtle eye cues are less important than head orientation, Bayern wrote. Predatory birds such as owls and goshawks turn their entire head when looking at a prey animal, although, by that time, it’s probably too late for Jackdaws to successfully react to a predator’s subtler eye movements, even if they are close enough to see them.
These findings are especially interesting because most other species investigated so far, including chimpanzees and dogs, are not very sensitive to eye orientation and eye gaze, von Bayern pointed out. Rather, she wrote, chimps and dogs seem to rely on other cues such as head or body orientation in determining the looking direction of others but don’t appear to appreciate the eyes as the visual organs.
“As it looks now, apes are surprisingly bad at looking at eyes, because it seems like other cues such as head direction are much more important [to them],” Bayern said. “But I think they understand a bit.”
This supports the theory that social sophistication may select for intelligence in evolution, Bayern said. Jackdaws are corvids, which are among the most intelligent groups of birds along with parrots.These results suggest that birds may deserve more respect for their mental abilities.
“We may have underestimated the psychological realms of birds,” von Bayern remarked. “Jackdaws, amongst many other birds, form pair bonds for life and need to closely coordinate and collaborate with their partner, which requires an efficient way of communicating and sensitivity to their partner’s perspective.”
Auguste M.P. von Bayern & Nathan J. Emery (2009). Jackdaws Respond to Human Attentional States and Communicative Cues in Different Contexts, Current Biology, 19 (7) DOI: 10.1016/j.cub.2009.02.062 [free PDF].
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Originally published at scienceblogs.com on 5 April 2009.