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Director Graham Russell tells us about the filming on ±«Óãtv Two's Inside The Animal Mind

Over the course of my TV career to date, I’ve had a fair few animal encounters. I’ve taught pigs how to navigate a maze. I’ve had my hands bitten by hundreds of leafcutter ants. But for me, in terms of intelligence, one creature stands out from all others - the New Caledonian Crow, and it’s rightly the star of episode 2 of Inside The Animal Mind.

I first met one in captivity. Superficially to me, it looked just like a normal carrion crow, but upon closer inspection, differences became apparent. The eyes were much bigger. The beak seemed stouter. Still a crow, however.

But, to paraphrase a high street retailer – this was not just any crow. This was a New Caledonian Crow.

My host, Dr Auguste Von Bayern from the University of Oxford, presented the crow with a log, in which a cavity had been carved. Into the cavity she placed a grub, the crow’s favourite food.

The bird investigated, and quickly discovered that the morsel of food was out of reach, safe within the wood. But all was not lost. Auguste placed a stick with a section of pipe-cleaner glued to one end within the aviary.

The bird hopped over, secured the stick in place with a claw, dipped its head to grab the pipe-cleaner end with its beak, then bent into a hook-shape. Which it then used to fish the grub out of the log.

The bird had made a tool and then used it for the purposes of hunting. I was flabbergasted. It turns out that what those strange eyes and beak are for – they've evolved to help these crows make and use tools.

But the crow’s abilities don’t end there – far from it.

When we arrived on New Caledonia, we were told the best chance we had of spotting crows in the wild was on a mountain road at daybreak. In recent years, it had become the norm for families of crows to gather in trees above a particular stretch of road, and use the tarmac (and cars travelling beneath) to crack nuts. Pretty clever – but not earth-shatteringly so. Crows in the UK have been observed doing something similar with mussels, again using the tarmac and cars to crack open shells.

But when we arrived, we noticed something else going on.

The road was on a relatively steep incline, snaking its way up the mountain, with a safety barrier running all the way along it. The local mayor, in a fit of jungle-based civic pride, had decided to hide the galvanised steel of the barrier inside a wooden cladding making it look, to all intents and purposes, like a nice wee wooden fence. So far, so aesthetically safety conscious.

The wood was bolted onto the metal, leaving deep circular holes on the outside of the barrier. And somebody noticed – I think it may have been Chris – that all of the holes were filled up with a weird assortment of debris. There were massive snail shells, nut fragments and what looked like bits of old flesh from indeterminate species. This pattern was repeated in every hole, of which there were many.

And then it dawned on us what was going on. Well, I say dawned. What I mean to say is we saw it in action.

We’d positioned ourselves quite far away from the crows – humans and camera lenses freak the crows out - and sure enough, we saw them dropping nuts onto the tarmac to crack the shells - just as we’d been promised. But they weren’t waiting for cars to finish them off. The birds quickly flew down after the nut, retrieved them, and took them directly to the safety barrier.

There, they placed them inside those holes – and then eat the nut. All that debris we’d seen within the safety barrier was the leftovers of many crow-meals.

But why do this? Well – the walls of the hole were must have been acting as a vice, holding the food tight and allowing the crow to eat more easily. It’s a clever solution – especially if your food’s in danger of rolling away down a hillside. But we think it’s more impressive than that.

The barrier – you’ll see it in the programme – was quite new. No more than a couple of years old. So the birds must have developed this strategy relatively recently – but now they all now do it. So in that short period of time, not only has the ‘idea’ been developed, it’s also been passed on to other birds. When these birds have a good idea, it quickly spreads through the other population.

These birds make tools, solve problems and take advantage of changes within their environment – it’s abilities like these that have led some people to call the crow family ‘feathered apes.’