Barbara Palmer, chief keeper of the big cats at the zoo, said Monday that Leanne, a 230-pound Sumatran tiger, is expected to give birth to between one and four as early as this weekend, the San Jose (Calif.) Mercury News reported Tuesday.

"There is no pregnancy test for cats, so we have to take our best guess," Palmer said.

Only about 400 Sumatran tigers are believed to still survive in the wild and about 60 of the big cats live in U.S. zoos.

The zoo also announced Monday that one of its female giraffes, Gezi, gave birth to a 150-pound baby.

"We are absolutely thrilled to have another giraffe born," said Bob Jenkins, director of animal care and conservation. "The herd of three females and one male giraffe has made the San Francisco Zoo's new African Savanna home since 2004."