It never fails to enthral me. You know a place reasonably well, and then you move just down the road and it’s completely different. It looks different and sounds different: and that’s because it’s different at some fundamental level. It’s called ecology and I heard its truth in the call of a purple crested turaco. It was crowing like a chicken stuck up a tree.

You sometimes see them in South Luangwa National Park in Zambia. But we were in North Luangwa National Park and in a place full of trees. That’s what purple crested turacos like: and that’s why their calls were ringing out again and again.

They’re birds worth taking a good look at as you glimpse them through the branches: green and purply-black, and then the wings flair out in a sudden glare of crimson. I have seen them often enough and always enjoyed them, but on this trip, they turned up so often that I understood something about them I had never realised before.

They can’t fly. Well, hardly. And that’s not what you expect from birds that live in trees: you’d think some sort of basic aerial competence was essential. But apparently not. They’re very agile, getting about their big-branched trees with a series of crazy hops, often with wings extended. They look confident, colourful and noisy.

But then they move onto the next tree – and ooh-er! It’s off with a mad flap and glide and what seems an extempore prayer: but after something between a plummet and a parachute they’ve made it safe and sound and are hopping about the next tree as if they owned the place.

There are plenty of just-abouters: birds that can only just about fly. But they’re always ground birds that get in the air only when they have to, mainly to escape a predator: birds like pheasants or red jungle-fowls, the ancestors of domestic chickens. But here are birds that live way above out heads – and they can only just about fly.

Don’t expect evolution to follow human logic. If it works it works. Purple crested turacos may not up there with eagles and albatrosses and swifts and hummingbirds but they can fly well enough to please themselves. There’s a moral there, no doubt – but come, it was time for a Mosi beer.

• I was co-leading a trip with Wildlife Worldwide https://www.wildlifeworldwide.com/discover/zambia