By Jonathan Webb
Science reporter, BBC News
23 December 2015
Ecologists have used a tail-mounted "crow cam" to catch wild New Caledonian crows in the act of making and using hook-shaped tools.
This species is well-known for its clever tool tricks, but studying its behaviour in the wild is difficult.
These tiny cameras peer forwards beneath the birds' bellies and record precious, uninhibited footage.
As well as glimpsing two crows making special foraging hooks, the team was able to track their activity over time.
This "activity budget" offers a rare insight into the natural lives of New Caledonian crows - but it has not yet solved the mystery of precisely what drives these birds to use tools.
When we got that footage it was a proper high-five moment in the field campDr Christian Rutz, University of St Andrews
That is the "big money question" according to senior author Christian Rutz, from the University of St Andrews in the UK.
"Why is it that New Caledonian crows use tools but other corvids don't? I think the answer to that lies in looking at their time budgets and figuring out how important tool use is in their everyday lives - what kinds of prey sources they tackle with tools," Dr Rutz told the BBC.
In nearly 12 hours of "crow cam" footage from 10 different birds, described in the journal Biology Letters, he and his team actually caught surprisingly little tool time on camera.
"Out of total observation time, only about 3% was spent making or using tools," Dr Rutz said. And only four of the 10 subjects picked up a tool at all.