Any day now, Robert Gramzay will witness the birth of a dozen babies he helped spawn.

As the senior keeper for the Central Park Zoo’s penguins, Mr. Gramzay and his team orchestrated an ambience conducive to breeding for the zoo’s 57 gentoo and chinstrap penguins. Their attempts to reproduce the natural environment seems to be effective, for the imminent births mark the 14th year since 1990 that the zoo has successfully hatched penguin chicks.

Mr. Gramzay, who has worked with the penguins since 1988, when the colony had just 34 birds, employs a seasoned strategy to motivate mating. Every April, he introduces rocks into the penguins’ habitat. Both males and females collect rocks to build a nest, which can be up to 2.5 feet wide and 1 foot tall. The rock-collecting behavior is triggered by the “photo period,” or the number of daylight hours.

“It tells them what time of year it is, and that kicks in their hormones, that starts the nest-building drive, and the instigation of the synchronized courtship dances,” Mr. Gramzay said.

Building the nest cements the bond between the pair, but penguins tend to be seasonally monogamous, Mr. Gramzay said, and they often move on to different partners the following year. After the female lays one or two eggs in the nest, the pair shares the incubation responsibility, but both parents are violently protective of their unborn children.

“We might be trying to feed the adult while the guard bird is trying to bite us, so we have to do that carefully,” Mr. Gramzay said.

After the chicks are born, weighing 80 to 100 grams, the keepers will give the parents extra food – usually fish – and encourage them to feed the chicks themselves. A biology professor at the University of Washington, Dee Boersma, told The New York Sun that breeding penguins in captivity is often safer than life in the wild.

“You do well when you are living at home with your parents, and you do less well when you have to leave,” Ms. Boersma, who has studied Magellanic penguins in Argentina since 1982, said.

In addition to providing a reliable food source, zoos can prevent penguins from encountering deleterious manmade obstacles.

“There are no oil spills in captivity,” Ms. Boersma said. “There are no predators. You don’t keep leopard seals in with the penguins. You’ve changed the chances of them being captured from predation or being caught in fishing nets.”

These penguins, natives of Antarctica, generally breed during the Southern Hemisphere’s summer, which falls during New York City’s winter. Mr. Gramzay said the timing of the breeding is dependent on the duration and intensity of the light in the habitat. On June 21, the summer solstice, the penguins experienced 18.5 hours of light. And in the winter months, the lights are on only during the hours the zoo is open.

A few years ago, the Boston-based New England Aquarium was having trouble breeding their penguins. They enlisted the help of lighting designer Alan Symonds, who was able to tweak the habitat’s conditions using a network of theatrical lights.

“We doubled the amount of lighting on the islands and installed timing to create a day/night cycle,” Mr. Symonds wrote in an e-mail. “The penguins responded quite well to improved lighting and started behaving happily. That led to more babies.”