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

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.

This technique is not easy. Birds need a lot of practice to pull it off and even veterans can spend a lot of time fishing out a single grub. The insects are fat, juicy and nutritious but do they really warrant the energy spent on extracting them? The answer is a resounding yes, according to Christian Rutz from the University of Oxford. By analysing feather and blood samples from individual crows, he found that grubs are so nutritious that just a few can satisfy a crow for a day.

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