Tool use and cognition, Part 2: Can water be a tool?

I promised that there would be actually spider monkey tales in here...


When I was studying the spider monkeys at Brookfield Zoo (summer 2007), Rita, the youngest of the group, did something really fascinating. She was trying to reach a food item (some kinda of leafy vegetable) that had fallen into the tapir's pool. So, using her spider monkey assets, she did what any spider would do: Anchor her tail to a support, and swing out to try to reach it. However, despite that long tail and long arms, and several swinging attempts, she could not reach out. Looking frustrated, she gave up. She sat there, gazing at the pool and the leaf for a couple minutes. And then, she got up, went to another spot closer to the leaf (that lacked supports for tail-anchoring). She was still to far to reach it, but she paddled the water, floating the leaf closer until she could pick it up and reach it.

Regardless of what to call it, this was a fascinating example of problem-solving. But, it got me thinking of whether manipulating water could be consider tool use. If water can be considered a detached object, it would meet the definition for tool use. But, given the weird and amorphous properties of water... I'm really not sure.

However, there's a couple studies that have specifically looked at water as a tool. In Raising the Level: Orangutans use Water as a Tool, Mendes, Hanus, and Call specifically investigate the use of water as a tool, and the orangs utilize water to float a peanut to the top of a tube. Similarly, in Rooks use Stones to Raise the Water Level to Reach a Floating Worm, Bird and Emery provide use inspiration from Aesop's fable "The Crow and the Pitcher," testing whether rooks can use stones to float a worm to the top of the container. The result is that rooks quickly figure out that they need to add stones to access the worm. You can watch these trials here, thanks to YouTube.

Based on these studies, it sounds like water does qualify as a tool. Furthermore, it really is a more impressive tool, since the animals need to understand water's properties. While the orang and rook studies involve using water to float and object to the top, it would be really interesting to see some studies that investigate the use of water to move an object horizontally closer, the way that Rita got the leaf. And perhaps we should being doing more of these cognitive studies with spider monkeys, so they can show off how smart they are :)