With its worldwide renown, the 103-year-old Bronx Zoo would seem to sell itself. But just like museums and national monuments, the Bronx Zoo ( faces the challenge of luring back visitors who think once is enough.

Though a nonprofit (run by the Wildlife Conservation Society), the zoo still needs to cover its costs, and make money to build new exhibits and continue its mission of preserving animal life. Though the zoo has used marketing and advertising for many years, it never struck gold until 2001, with its “Oh, Baby!” campaign. Ninety percent of surveyed adults remembered these ads, compared with a 65 percent awareness rate previously. And 35 percent of people polled at the zoo gate said they came to the zoo to see the new babies.

The zoo is building on the idea this year by featuring not only new babies, but animal tots as old as the “Terribly Terrific Twos.” And it’s branching beyond ticket sales: The zoo recently struck a publishing deal with Scholastic to produce a book about the animal babies, and has another potential deal with FAO Schwarz to tie in the zoo babies with the store’s own “Oh, Baby!” line of products.

The lesson? When an idea works, stick with it. Lesson number two? The old tongue-in-cheek adage of successful advertising — “When all else fails, use a puppy or a baby” — might have something to it. After all, the Bronx Zoo did a little of both.