"Just set the camera over there with the test, and I'll be back in five minutes." It was to prove to be an eventful five minutes.

Who's a clever kea, then?
We were filming keas in the snowy mountains of New Zealand's South Island, and we'd built an intelligence test to discover just how clever these alpine parrots really are. But this depended on a lot of assumptions: that we would find wild birds, that we could get near to them, that they'd approach the puzzle and that they really were intelligent enough to work out how to get their food reward - by pulling a string, standing on the string to stop the food falling back again and repeating this action several times, with a camera pointing at them close by.

I returned to find cameraman Paul Donovan relaxing in the carpark. He was at his most laconic. "We allowed four days for this shoot, didn't we?" he asked. "Thereabouts." "Well," said Paul, "they've done it in under three minutes. I filmed it. And you missed it. Coffee?"

Testing times
I was amazed. I'd done many similar tests over the years with different bird species - tits, pigeons, crows, even woodpeckers. But in each case, the birds took days, weeks or months to solve the tests. It was obvious our intelligence tests were way too simple for these keas. So kea experts got together to design the most fiendishly difficult test that humans can devise for bird. We've filmed rooks discovering an ingenious way of breaking open walnuts, ravens solving four-stage intelligence tests, pigeons distinguishing between different colours to get a food reward.

Likeable rogues
And then there are the keas - the only true alpine parrots in the world, confined to the high country of New Zealand's South Island. Their dark, olive-green plumage, heavy bodies and long bills tucked back into their stubby necks might make them look drab. But as one takes off and lifts its wings, you see a glorious splash of extravagant orangey red on the underside of the wings. Any New Zealander will tell you the kea is bold and cheeky - a likeable rogue.

In their harsh mountain environment, food is hard to get. They must be ready to take advantage of any food that's available. Be unselective in their diet, or die. Be ingenious in finding new food sources, or die. Be flexible in their behaviour, or die.