A new paper in Nature Communications by Tomas Bugnhyar, Stepehen Reber, and Cameron Buckner (free download; reference below) examines the question of whether ravens, already known to be really smart, have a “theory of mind.”
What do we mean by that? Well, according to the authors, a “theory of mind’ means that animals can have a representation of an action performed by other animals, and then act on that representation rather than having to see the action itself. In other words, the animal imagines that another individual of its species is around, and then, without using visual cues, acts according to what it thinks the other animal is thinking and will do.
To be specific, in this case the researchers studied the behavior of ravens in caching food, and how that ability changed if the ravens thought another individual was around but couldn’t see it.
It’s been known for a while that when corvids, like ravens and scrub-jays, are caching food—burying it underground to hide it—their behavior changes if they know another individual is around. They may then re-cache it, burying it in another place so their food isn’t purloined. Other ways they protect their caches are hiding them behind obstacles, interrupting their caching when they see another bird, and staying away from already-cached food so as not to attract the competitor’s attention to the location.
In such cases, the birds (mostly scrub-jays in these studies) clearly are reacting to the stimulus of seeing another bird, and, through either learning or evolution, behaving in a way to hide their food, which is clearly an adaptive act.
According to the authors, previous experiments like this don’t really address whether the birds have a “theory of mind”, that is, an imaginative representation of what the other bird might be thinking, because they can actually see the other bird. As the authors say, these experiments suffer from the problem of being “unable to empirically distinguish representations of directly observable cues from a genuine representation of ‘seeing’.”
In this experiment, the authors tried to get around this problem by watching ravens cache when they didn’t see any competitor ravens, but thought they were around because raven noises were played. There was thus no chance that the ravens were acting on “gaze cues” sent by another bird. The authors did this by making peepholes between rooms represent the assumed presence of competitor ravens.
Birds were allowed to cache bits of cheese and dog food in one of two adjoining rooms. The rooms were connected by a window that could be closed, as well as a peephole that could be blocked. The ravens were also trained to know what the peepholes were for, as they learned to look through them and see a human caching food in the next room, and then were allowed to go into that room to recover the food. They thus learned that the holes were a way to see into the adjacent room, even though they couldn’t see through them unless their eyes were right up against those peepholes.
The initial predictions of the experimenter were, if ravens had a representation in their minds of what another raven in the next room would be thinking or would do, that:
- Ravens would cache their food more rapidly if the peephole were visible (and they could hear raven noises) than if the peephole were not visible. (Peepholes were obscured with a board.) That would mean that they carried the idea that another raven might be looking through the peephole at them, watching them cache. In such cases they’d finish up caching as soon as possible. They could not see a raven through the peephole, as there were none in the next room, but they could hear raven noises. Their caching behavior is expected to resemble the behaviors performed when the windows were open and they could see and hear a raven in the next room.
- In the same way, a visible peephole was predicted to make the ravens less likely to “improve” their cache: go back and recache or change the layout. That behavior calls attention to possible competitors (as noted above), and so a reduction in “improvement” means that the birds thought another raven could see them through the peephole.
This protocol, then, involves three experiments, as shown below: bird caching while seeing another raven observing it (a); bird caching with another bird in the next room that it couldn’t see, but could hear (b); and peephole with no bird in the next room (c). Raven noises were played to the caching bird in all three conditions. All ravens were hand-reared and, while trained in cognition studies, had no experience with caching, either with or without other ravens nearby.
To ensure that ravens weren’t operating because they’d seen another raven watch them before (even before they reacted to the peephole), trials b and c were given first. Birds were then exposed to a (open window) and then b and c repeated.
The results are given in the graphs below, and confirm both of the authors’ predictions:
- Ravens subject to the peepholes and windows (“peep” and “obs” respectively) cached for significantly shorter times than ravens who could not see the bird in the next room, even though raven noses were played. That’s shown in (a) below. Conditions connected with a line show that those comparisons were either significant (*) or not significant (NS). The duration of caching was, on average, about 14 seconds when they couldn’t see the neighbor raven watching, but were significantly reduced to 7-8 second when either the peephole was visible or the window was open. There was no difference between the peephole and open-window conditions, suggesting that ravens construed the peephole as if it denoted “another raven is watching”.
- As predicted, ravens “improved” their caches less often when the peephole was visible, or when the window showed another raven next door, than when the window was closed. Plot (b) shows this difference. Again, there is no difference between “open window” and “peephole” conditions.
Note that raven noises were played in all conditions, so the differences seen can’t simply be ascribed to hearing a competitor. No, there must be something about ravens thinking they’re being watched that explains the peephole results.
Does this show that ravens really do have a “theory of mind”? Well, it shows that ravens can act on the basis of assumed behaviors without having to see other animals. They think they’re being watched because they associate the peephole with vision, and so are acting on assumptions rather than observed behaviors. If that is a theory of mind, then ravens have one. Draw your own conclusions.
Let me add one more thing: the ravens altered their caching behaviors without ever having to suffer the loss of their cache to a competitor. Indeed, they altered their behaviors without ever having seen a competitor raven in the next room. To me this suggests that the caching behavior, and the way it changed under the assumption of a nearby competitor, are evolved rather than learned traits. These were naive ravens, and had no experience in nature before the experiment.
UPDATE: A reader suggested that maybe evolution of this type isn’t involved, and that the ravens may be generalizing from their own behavior. That is, perhaps their behavior stemmed from watching through the peephole and seeing the humans cache food, and then going into that room and retrieving the food. They could then assume that if another raven is around, it would do what they did—retrieve food. That is still a theory of mind, but doesn’t necessarily involve evolved propensities to behave differently when you think a conspecific is around.
But how to determine if re-caching is evolved? I think one can expose naive ravens to another raven without any training. Having it cache food (presumably that is evolved), and see if it recaches if another raven is visible compared to the window open with no raven visible. It could be using behavioral cues, but those cues would have to act on an evolutionary program if they caused naive ravens to change their caching behavior.
Bugnyar, T., S. A. Reber, and C. Buckner. 2016. Ravens attribute visual access to unseen competitors. Nat Commun 7. Article number:10506doi:10.1038/ncomms10506