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Bird tool use evolved for better grub, literally

Image: Bird tools
Simon Walker
/ Source: Discovery Channel

Some birds, such as New Caledonian crows, use sticks as tools, and now researchers think they know why: better grub. The discovery helps to explain how and why tool use first evolved, but the answer isn't quite as obvious as you might think.

Tools don't always provide the fastest, easiest solution to problems. In the case of New Caledonian crows, for example, their usage of sticks to dislodge wood-boring beetle grubs from rotting tree trunks requires a lot of time and practice. Why do crows even bother with the sticks then?

Christian Rutz of the University of Oxford and colleagues investigated the benefits of this tool use by analyzing how the beetle larvae contribute to individual crows' diets. Since the beetles themselves have a distinctive diet- wood- they carry a unique isotopic signature. The scientists traced this signature in the feathers and blood of wild crows. Rutz and his team next created a model to estimate how much energy this food source gave to the crows.

The researchers determined that just a few larvae can satisfy a crow’s daily energy requirements. It may take seemingly forever for one of these birds to strike grub gold with a stick tool, but the effort turns out to be worth it. What to us appears to be a minuscule grub is like a protein-packed juicy steak to a crow.

The findings, published in the latest Science journal, highlight the substantial rewards available to adept tool users and their offspring, helping to explain how tool wielding emerges and spreads throughout animal populations.