If pigeons could giggle, these would

Why do cats climb trees? Because they are there. It's the Everest challenge for felines. Of course there may be secondary reasons. For instance, cats instinctively know that trees are a trump card in the age-old sport of chase-me, don't-chase-me that they play with dogs.

Our little black cat is a house cat, so he shins up chair backs and scrambles onto bookshelves. The shelves are made of wood, so I suppose they remind him of trees.

Another secondary reason is the matter of birds. Even the nicest domestic cat unfortunately tends to see a bird in just the same way that the nicest bird tends to see a worm - as dinner. With cats, though, this may have no observable connection with genuine hunger. You can ladle out the best supermarket cat food every passing hour with an overweening generosity that reasons not your cat's needs, yet your overfed friend will still fancy a sparrow.

But our black, indoor cat frequently scales the highest reaches of my bookshelves even though no sparrows live up there and the dogs are sound asleep and completely indifferent to his antics.

In other words, I am convinced he just climbs my books for the sheer joy of it, leaping and clinging like a squirrel, finally perching atop "Far From the Madding Crowd" or Claes Oldenburg's "Drawings and Prints" with a look of elevated triumph on his owl-face that means, quite simply, "Look at me! There's no business like show business! I can do anything better than you!"

Famously, of course, although cats ascend trunk and branch with consummate skill, they are often not quite so good at descent. The fire brigade sometimes has to be summoned. Or at least an athletic friend or relation.

The young son of some friends of ours told me how, when he was much younger, his tiny kitten once climbed a tall, dense conifer in their garden. A sad thin cry let the family know where the kitten was, and also plaintively suggested that it was stuck.

So an older brother of known gymnastic prowess agreed that he would climb the tree equipped with a bag in which to put the kitten and bring it safely home.

Up went the intrepid brother, and when he reached the lofty animal at last, instead of encountering a terrified and dizzy creature, what he found was a kitten sound asleep and curled up cozily in an empty, feather-and-moss-lined bird's nest.

I liked this tale so much that I have re-told it to a friend or two. One of them said that one of their cats loves tree climbing so much that her partner is persuaded he will build a cat nest for it up its favorite tree. That's cat lovers for you.

While I was passing the kitten story round this week, a presenter on breakfast-time TV, during a review of the British newspapers, held up a photograph in one of the less-serious dailies of a small dog up a tree. It sounds as though this somewhat unusual dog mistakes itself for a cat. Perhaps it was reared among cats and hasn't ever looked in a mirror.

Anyway, there it was, sitting, completely at home, wedged satisfactorily and high up where two substantial branches branched. And again it looked as though it had done so for no better reason than that it liked to do it.

And why shouldn't it?

Generally, birds don't think twice about trees as natural perching places, but one day when I was walking in a local park and skirting around a pond, I happened to look up into a rather fine Scotch pine that grows nearby. And there, resting on a spreading limb, sat a duck. I hadn't seen a duck up a tree before.

I am not sure whether this is a more common duck practice than I realize, but my long acquaintance with ducks suggests that they are basically a ground or water-level bird and there was, to me, something oddly inappropriate about this arboreal duck. As I stared at it, as if it were suddenly embarrassed by its unconventionality, it lifted off and flew away through the wood. I have never seen a duck up a tree since.

I suppose there are naturalists and scientists who refuse to countenance the notion that creatures wild or tame do certain things for no other reason than pure enjoyment. If so, let me say that I don't give a bean for their unimaginative conclusions. I mean, how else would they explain our pair of pigeons?

These pigeons are decidedly "ours." They are forever gorging themselves at our bird table.

But when they are waiting for a fresh supply, or contentedly digesting what they have just eaten, they have a favorite perching place a few yards away that I am convinced not only appeals to them as convenient, but also because it is nothing more nor less than fun. It is kinetic.

We commissioned it a few years ago from an excellent and highly imaginative sculptor in steel named John Creed. We asked him to make something that would be both a weather vane (but definitely not a typical one) and at the same time an abstract sculpture. He produced a beautiful, elegant, thoughtfully symbolic structure that stands in our garden. We see it from various windows and love it for its quiet response to the frequently changing direction of the Scottish winds that playfully invade or variously maelstrom round the garden.

The revolving element has a rudderlike fin at one end, and, at the other end, a flat "pointer" about three feet long and three inches wide. The pigeons have adopted this flat pointer and made it their own. And when the winds move it, far from flying off in sudden alarm, they just sit there, unruffled, balanced, with the smuggest expressions on their faces. They clearly enjoy the ride.

Round and round they go, like fairground horses. And I swear that if laughter were a pigeon thing, the sound of merry pigeon chuckles would waft away on the breezes.