Call it a GoCro. Cameras mounted on the tails of wild New Caledonian crows have caught these renowned tool-makers in the act of creating the hooked foraging implements from plants.
New Caledonian crows are the only non-human animals to make hooked tools in the wild. Why they do so is something of a mystery. “The answer to that lies most probably in the ecology of the place and the ecology of these birds,” saysChristian Rutz at the University of St Andrews, UK.
Filming their natural behaviour may help us get to the bottom of it.
Back in 2007, Rutz and colleagues equipped crows with video cameras to film their behaviour in the wild. They were able to transmit live pictures, but the range was short, so they had to follow the birds around and the signal would sometimes cut out.
Now Rutz and colleagues have followed the behaviour of 10 crows in a new study with a better camera setup. This enabled them to record about an hour of footage for each bird. They found only four of them used tools during the recording sessions.
It’s unclear whether some crows don’t use tools at all, or if they just didn’t in the time recorded. “I think that’s a very interesting lead for future research,” says Rutz.
The film captures crows manufacturing tools in the wild, which they did from paperbark and a local plant, Acacia spirorbis. They first snapped a twig just above and below a branch, then stripped the bark and leaves from the longer, thinner branch and crafted the cut ends to make a hook.
Crows used the hooks to extract insect larvae, and on one occasion an adult insect, from wood. They were also spotted using hooked tools to forage in leaf litter, which hasn’t been seen before.
The cameras also captured plenty of foraging behaviour without tools, including one bird catching a frog and feeding portions of it to chicks.
“These birds very frequently switch between tool use and bill foraging,” says Rutz. “It’s this switching that to me is quite interesting, because it shows that for certain foraging tasks, the bill presumably is sufficient, and for others, when it comes to extracting grubs, for example, from dead wood, you need a tool.”
Journal reference: Biology Letters, DOI: 10.1098/rsbl.2015.0777