Washington ? It’s spring, and the National Zoo seems to be full of babies and youngsters, planned and unplanned.

For many species, especially the larger ones, zookeepers use birth control or separate enclosures to prevent pregnancies and overpopulation. With endangered species, most pregnancies require approval of a nationwide committee of zoo officials, who consider factors such as the need for genetic diversity. But in some smaller species for which overpopulation is not a problem, zoos let nature take its course.

Whatever the reason they came into being, these small creatures delight visitors. They bring more visitors to the zoo, a welcome antidote to last year’s tourism slump, and they offer a cheerful change for a zoo staff increasingly preoccupied with caring for aged animals.

There is baby Berani, a new member of the endangered Sumatran tiger species. Kandula, an Asian elephant, weighed 325 pounds at birth in November. A not-yet-named male lowland gorilla, also born in November, still clings to his mother much of the time. Ripley, a Sulawesi macaque monkey, loves to smack his lips for visitors.

A threesome of black-necked swan cygnets ride on their parents’ backs, and, out of view, small crayfish molt and grow.

At the Great Cats exhibit on a sunny day last week, a crowd of parents and children leaned over the fence to watch 6-month-old Berani’s every move, offering play-by-play commentary.

“There he is!” one child shouted.

“Pouncing on mom!”

“Almost got that bird!”

His mother, Soyono, romped alongside her 64-pound youngster. But finally, she declared her limit, batting the baby with her paw to signal that it was time to stop bothering her.

In the macaque area, young Ripley, born in December, is also drawing crowds. Sulawesi macaques are found on an Indonesian island.

“He’s eating solids, and he is into everything  very curious, kind of a troublemaker,” said Nicole Meese, a primate and panda keeper. “Now that he is growing older, the adults are a lot less tolerant.”

Ripley, who weighs only a kilogram or two, was a surprise birth. He is the first offspring of 11-year-old Raya. The father could be any of the three males in the group of macaques; paternity tests are under way.

Another unplanned birth was the trio of cygnets born March 19 to the zoo’s two black-necked swans. It was a cold day, but the birds were not bothered because they come from a cold environment in southern South America, according to senior keeper Debi Talbott.

While not endangered, the birds are not prolific in captivity either, so zoo officials were pleased at the births.