London :Crows too can learn to fashion complex tools, say scientists who captured first video recordings of wild crows making and using ‘hooked stick tools’ to hunt for insect prey in the wild.
Jolyon Troscianko, from the University of Exeter, and Christian Rutz, from the University of St Andrews, have captured video recordings documenting how New Caledonian crows (Corvus moneduloides), found on the island of New Caledonia, fashion these particularly complex tools in the wild.
The researchers developed tiny video ‘spy-cameras’ which were attached to the crows, to observe their natural foraging behaviour.
They discovered two instances of hooked stick tool making on the footage they recorded, with one crow spending a minute making the tool, before using it to probe for food in tree crevices and even in leaf litter on the ground.
“While fieldworkers had previously obtained brief glimpses of hooked stick tool manufacture, the only video footage to date came from baited feeding sites, where tool raw materials and probing tasks had been provided to crows by scientists,” said Troscianko.
“We were keen to get close-up video of birds making these tools under completely natural conditions,” he said. “By documenting their fascinating behaviour with this new camera technology, we obtained valuable insights into the importance of tools in their daily search for food,” he said.
To obtain a ‘crow’s-eye view’ of this elusive behaviour, the two researchers developed video cameras that are attached to the crows’ tail feathers.
The cameras are about the weight of a British 2-pound coin, and a tiny integrated radio beacon let the scientists recover the devices once they had safely detached after a few days.
“These cameras store video footage on a micro-SD card, using technology similar to that found in people’s smart phones. This produced video recordings of stunning quality,” said Christian Rutz, from St Andrews.
The team deployed 19 cameras on crows at their chosen dry forest study site, where in hundreds of hours of fieldwork, despite two brief glimpses with binoculars, they had never managed to film crows manufacturing hooked stick tools.
The researchers recorded two instances of this behaviour on footage recovered from ten birds in their latest study.
“The behaviour is easy to miss the first time I watched the footage, I didn’t see anything particularly interesting. Only when I went through it again frame-by-frame, I discovered this fascinating behaviour,” said Troscianko.
“In one scene, a crow drops its tool, and then recovers it from the ground shortly afterwards, suggesting they value their tools and don’t simply discard them after a single use,” he said. The study was published in the journal Biology Letters.