Most humans don't consider bird brains to be particularly impressive. Witness the fact that `bird brain' is an insult used to denote stupidity in humans. Perhaps some birds are not particularly intelligent by human standards(especially the ones that we have bred for eating). However, there are avian species with cognitive powers on a par with those observed in many primates. In particular, birds in the genus Corvus (crows, ravens, jackdaws and rooks) are good examples of just how intelligent birds can evolve to be.

That said, not all corvid behavior makes sense at first glance. For example, ravens (Corvus corax) commonly bury brightly colored objects in the presence of other ravens and human handlers. The birds do this in plain view, and the objects they hide have no obvious value. This behavior, termed`play caching', has puzzled researchers for years. After all, it's not as if ravens don't know how to hide things. Food items, for one, are buried out of sight, with the utmost care and secrecy. So why would a raven waste energy doing this seemingly silly public behavior? Thomas Bugnyar and colleagues at the University of Vienna recently asked this question, then tested the idea that ravens use the experience as a way to gauge whether or not other individuals have a tendency to steal.

In their first set of experiments, Bugnyar and colleagues gave brightly colored baubles to hand-raised ravens, then gave the birds a chance to bury their treasures on a snowy forest floor. Two new researchers then stepped in and played good cop–bad cop. One researcher (O) simply inspected every hiding spot; the second individual (P) inspected, then blatantly pilfered every cache.

How did the ravens react? In both situations, ravens tended to inspect both sites after the humans had left the scene. The birds were clearly curious to see what O and P had been up to. The birds responded by changing the location of subsequent caches relative to both observers. Overall, they buried items progressively farther and farther away from the humans. However, despite having been robbed the first time, the ravens reacted by shifting the cache closer to P than to O. They behaved as if they were testing P. Notably, the ravens made no attempt to modify other aspects of their caching strategy across training sessions. In particular, they continued to cache in plain site of P, and did not attempt to camouflage their stashes more carefully in the presence of the pilferer. P kept stealing their baubles and the ravens just stood by and watched.

But does this mean that the ravens weren't learning anything about P? In the second set of experiments, the team tested how ravens cached items of real value (i.e. food items) given to them by O, P and a neutral observer (N). In the presence of P, the ravens started caching earlier than in the presence of O and N. Furthermore, they placed their food stashes behind obstacles, and took a longer time covering the items than in the presence of non-pilferers. These data suggest that the human researchers had become the researched. Ravens had learned from their play caching experiments that P was prone to thieving.

The experiments of Bugnyar and coworkers provide evidence that ravens can actually be pretty good scientists; they can use play behavior as a tool to probe the minds of competitors. Humans and some non-human mammals can also do this but, so far, this ability has not been widely documented in other animal phyla. This work adds to the growing body of evidence suggesting that the complexity of corvid social behavior can rival that seen in many mammals.

Just as importantly, Bugnyar and colleagues' work gives neurobiologists a taste of what else is out there ready to be worked on. The neural mechanisms underlying raven behavior are largely unknown. Compared with other bird species, we know relatively little about neuroanatomy and neurophysiology in the raven, crow and brethren. The richness and complexity of behavior in these species suggests that the corvid bird brain is actually a wondrous place, a place just waiting to be explored by neurobiologists.

Bugnyar, T., Schwab, C., Schloegl, C., Kotrschal, K. and Heinrich, B. (
). Ravens judge competitors through experience with play caching.
Curr. Biol.