[LINK] "Fishing for fat: why learning to use tools is worth it for the New Caledonian crow"

[rfmcdonald]

The Discover magazine blog Not Rocket Science has just reported on a new study examining the famous tool use of the New Caledonian crow: why did the species adopt this complex trait?

In New Caledonia, an island off the eastern coast of Australia, a crow is hunting for beetle grubs. The larvae are hidden within a decaying tree trunk, which might seem like an impregnable fortress. But the New Caledonian crow is smarter than the average bird. It uses a stick to probe the tunnels where the grubs are sheltered. The grubs bite at intruders with powerful jaws but here, that defensive reflex seals their fate; when they latch onto the stick, the crow pulls them out.

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The New Caledonian crow is one of the most accomplished tool users of all animals. They produce at least four different types from sticks and grass stems. Their tools have complicated shapes and are manufactured through a process that involves several steps. They can pick the best tools for the job, adjust their size and shape to suit their needs, combine them in sequence to complete a task, and create “meta-tools” by using one tool to get at another. They can make tools out of unfamiliar materials, like coat hangers.

[. . .]

Rutz found that the grubs provide the crows with about as much protein as all the other sources, but they contribute almost half of the fat in the birds’ diet. On average, the crows eat just under two grubs a day, and Rutz calculated that they would only need 3 to meet their entire energy needs.

This shows that an enterprising crow gets tremendous benefits from investing the time and effort it takes to use tools properly. Indeed, young crows can spend years fiddling with their tools to no avail. It’s an unrewarding period, but it eventually pays off.

Interestingly, humans may have played a role in the tool use by creating an ecological niche where tool use would be useful. If so, clearly the crow's smart.

The presence of such an untapped source of energy may have spurred the evolution of the New Caledonian crow’s tool-making prowess. But Rutz thinks that early humans may have inadvertently nudged this process along. On New Caledonia, beetle grubs burrow into the logs of decaying candlenut trees, but these trees were only introduced to the island by prehistoric humans. The trees also provide nuts – the second most important source of fats and proteins for the crow. Rutz suggests that this sudden influx of nutrients might have been a key event in the evolution of one of the world’s smartest birds.