A team of scientists from the United Kingdom has captured first video recordings documenting how New Caledonian crows (Corvus moneduloides) make ‘hooked stick tools’ in the wild.
A New Caledonian crow (Corvus moneduloides). Image credit: Jolyon Troscianko.
New Caledonian crows – a species of oscine passerine bird found on the South Pacific island of New Caledonia – are renowned for their unusually sophisticated tool behavior.
However, despite years of studies, very little is known about how they make and use their foraging tools in the wild, which is owing to the difficulties in observing these shy birds, according to Dr Jolyon Troscianko of the University of Exeter and Dr Christian Rutz of the University of Oxford.
“Our video-loggers provided first footage of crows manufacturing, and using, one of their most complex tool types – hooked stick tools – under completely natural foraging conditions,” the researchers said.
The team developed miniature video cameras which were attached to wild-caught New Caledonian crows, to observe their natural foraging behavior.
The cameras were designed to detach safely after about one week, which allowed the scientists to recover them for data download.
“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,” Dr Rutz said.
The scientists deployed 19 cameras on the birds at their chosen dry forest study site.
They were excited to record 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.
“We recorded manufacture from live branches of paperbark (Melaleuca sp.) and another tree species (thought to be Acacia spirorbis), and deployment of tools in a range of contexts, including on the forest floor,” Dr Troscianko and Dr Rutz said.
“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,” Dr Troscianko said.
“This observation agrees with recent aviary experiments conducted by the group,” Dr Rutz added.
“Crows really hate losing their tools, and will use all sorts of tricks to keep them safe. We even observed them storing tools temporarily in tree holes, the same way a human would put a treasured pen into a pen holder.”
The findings were published online December 23 in the journal Biology Letters.
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Jolyon Troscianko & Christian Rutz. Activity profiles and hook-tool use of New Caledonian crows recorded by bird-borne video cameras. Biology Letters, published online December 23, 2015; doi: 10.1098/rsbl.2015.0777
