Nature is slow, yes. Nature takes her time. Nature does not fail.

For example, everyone knows the yellow-fronted gardener, one of the superb bowerbirds of New Guinea. The bowerbirds build bowers. Some build walled avenues, through which they parade to excite the female bowerbird (sometimes knocking down the walls in their displays) while others make platforms decorated with hundreds of flowers (which they change every day or so) and fruit and shells and (in civilized areas) clothespins and bits of plastic.

The yellow-fronted gardener bowerbird builds his bower four feet high in a Maypole arrangement of crossed twigs supported by some sapling. At the base is a mossy platform the size of a large washtub, on which he sets three piles of fruit, colored yellow, blue and green.

The thing is, this bowerbird is known only from three skins sold by a feather merchant to Lord Rothschild in 1895. All the other sorts of bowerbirds and birds of paradise are fairly well known to science, but not this one.

For all we knew, it was extinct.

But now it has been discovered in remote mountains of New Guinea. The discoverer, Dr. Jared M. Diamond, has made numerous expeditions to New Guinea looking for birds, supported by the National Geographic Society, the World Wildlife Fund and other bird-minded institutions. He reported yesterday to the Geographic on his discovery of this fabulous bird.

He found the birds so tame he could approach them closely. He is a membrane physiologist at the University of California, Los Angeles, in the medical school, and bird studies are his secondary, but still quite serious, profession.

He was in New Guinea to help that new nation plan national parks. The first day of his encampment, while thinking of other things entirely, he beheld this almost mythical bowerbird.

"I was in a state of suspense," he said. It seemed, after all, odd to find almost instantly a bird rarity commonly dreamed of by ornithologists. He then saw a courtship display, in which the yellow-fronted gardener raised his golden crest and made wonderful sounds, imitating gravel rolling down a hill, and imitating a nuthatch and a toad. He played a tape he had made, and whatever else is to be said of this bowerbird, at least it does not merely go tch-tch like other birds.

"I did not collect any of the birds," he said. He saw 30 and heard another 30 and he estimates there may be l,000 of these wonderful creatures about the size of a bluejay, only without long tails. They live at elevations of 4,000 to 5,000 feet above the sea, he reckons, and they are fearless because (this will hurt) they do not know mankind.

Even more greatly delayed than the bowerbird, who was at least heard from in 1895, is the English wild black fox. The last sighting of this elegant mutant of the ordinary red fox appears to have been 150 years ago.

The Observer, an English publication of exceptional alertness and judgment, found out about the recent sighting of the black fox and ran a photograph of it in color. It is withholding the geographical location of the fox, as well as the name of the family that sighted it. Otherwise, of course, the world would beat a barren path thither, to the detriment of the fox's wild habitat.

"Exclusive Photographs, the First Ever of a Black Fox, not Seen in the Wild in Britain for l50 Years," cries The Observer, which has given up English restraint but has forged ahead in the cutting edge of the news. The beast is shown to be exactly like a regular fox, only black, with a white tip to the tail.

The discoverers put out food for birds on their back porch. They were astonished one night to turn on the porch light and see the male black fox munching on some bread.

The fox began to arrive nightly. Then in the daytime, too.

"He sometimes sniffs our hands," report the family who feed him. "The sight of him sitting there, making sweet big eyes is reward and satisfaction enough. He's made two quick trips inside the house . . ."

The Lord only knows how it will all end.

Elsewhere on the Nature front (delayed appearances department) there is Rip van Snail, also English, needless to say.

Joseph Bell, 74, formerly a coal miner, acquired a pretty shell at the seashore. Three years ago he varnished it, for shells commonly lose their luster when brought indoors. But without warning, three years after sitting about as an ornament, the shell sprang to life and started walking around.

The same sort of shelled creature once lived for two years in the British Museum without eating anything, but Bell's snail holds the record. The snail inside is presumed to have been hibernating ever since he was varnished.

The former ornament has been eating cabbage and was scheduled, by Bell, to be returned to the shore yesterday.