How crows mastered the art of tool use

Tool use is incredibly rare in the animal kingdom, so it's a big deal when we discover crows going to considerable trouble to use sticks for hunting beetle larvae hiding inside branches.

Using a tiny stick might not seem like much, but it's the crow equivalent of piloting a 747 or running a particle accelerator - it takes years of training to master and it's still pretty difficult even for experts at the practice. The crows, found on the Pacific island of New Caledonia, also have to make the decision to learn how to use the sticks when they are very young, or else they won't be able to pick up the skill later. So why do crows bother with something so brutally complicated?

The answer lies in their diets. Oxford researcher Christian Rutz examined what the beetle larvae contribute to the crows' overall nutrition. They were able to do this because the larvae carry nitrogen-fixing symbionts, which shows up in the blood and feathers of crows who eat them but are absent in those that lack the tool skills to get at the larvae.

Rutz discovered just a few larvae can satisfy a crow's energy needs for an entire day, meaning a crow can almost immediately make up for the huge amount of time it had to put into getting the larvae. Nothing the crows would otherwise eat can compare to the raw energy content of the beetle larvae, which provides a major advantage to crows that can use tools.

Let's just hope it's not too much of an evolutionary advantage, or else we could be looking at a nightmarish Planet of the Crows scenario in a few million years. There's a reason a group of crows is called a murder, after all.

[Science]