THE vertebrate brain is an astonishing entity which has reached the peak of development (as far as we know) in us humans. The human brain is in fact the most complex thing known to science – far more intricate than any computer.

Our brains cannot operate at full power constantly; they need time to rest, recuperate and repair – a process that we call sleep. Almost all vertebrates do the same but what constitutes a nap in mammals can be very different in birds, and especially so in reptiles, amphibians and fish.

One of the first practicalities that an animal has to consider is how and where to fall asleep. In common with cats and dogs, we usually sleep lying down, but many other creatures prefer to doze off while standing up - horses, cows and elephants for instance. Many tree-living birds do the same by locking their claws shut around a branch, thus removing the requirement to think about holding on.

One of Ryedale’s most loved birds has a pretty unique sleep problem. The lifestyle of an adult common swift is so aerial that nesting is the only time they touch solid ground.

From May to August every year they raise their young on tall buildings in our towns and villages but they have all now left for their wintering grounds in Africa and will not land until next summer.

As I watched this year’s swift nestlings leave their nests beneath the eaves of the Grapes Inn in Slingsby, I was mindful of the fact that they would now be on the wing for two years, because swifts do not breed in their first year.

Which begs the question, “How do they sleep?”, and the astonishing answer is that they do it while they are flying. It’s thought that swifts climb up to an altitude of more than 20,000ft and then slowly glide back down, snoozing en route.

Scientists studying frigatebirds in the tropics noticed them doing something similar to swifts, but this time soaring upwards on thermals rather than coming down.

Frigatebirds are big birds so it was possible to fit tiny electroencephalographs to their skulls and monitor brain activity as they flew.

Sure enough, it turned out that the birds were sleeping as they circled but with only half of their brain.

When the right side of the brain was shut down the left side would monitor the bird’s open right eye. This allowed them to see while flying clockwise then, after a while, they would switch and go anticlockwise with the left half of the brain asleep – brilliant.

In my experience the local Yorkshire animals that seem to enjoy sleeping the most are our grey seals. The nearest colony to us in Ryedale is just down the road at Ravenscar, near Robin Hood’s Bay and on a calm and sunny day last month I kayaked out from Boggle Hole to see them.

At low tide the seals haul themselves out of the water onto a wide expanse of flat rock called Peak Scar. Here, in the shadow of Ravenscar’s towering cliffs over a hundred of them lie and sleep for hours, allowing their stomachs full of fish to digest.

With dry land not being their true element they are never completely at ease though, and always seem to sleep lightly with one eye open. Any disturbance from people walking too close or boats approaching and the animals will wriggle into the water en masse like a swarm of giant maggots.

Floating in the water is a different kettle of fish, if you’ll pardon the pun, as this is where seals feel most relaxed.

They will often drop off into a deep sleep while bobbing on the surface of the sea and with heads pointing straight up, presumably to keep water from splashing into their nostrils.

I managed to approach one snoozing adult female so close without waking her that I could hear her snoring and see the drool dribbling down her chin … it’s nice to know it’s not just me.

The click of my camera woke her with a start and she disappeared underwater in a flustered flap of flippers – the seal equivalent of a rude alarm clock wakening, I suppose.