The Christmas spirit may not have reached the tigers...

A 350-pound (140 kg) Siberian tiger mauled an experienced San Francisco Zoo keeper so badly she could lose her arm, even if the woman underwent emergency surgery at San Francisco General Hospital to save her limb.

"At least 50 visitors were at the zoo's big cat exhibit, called the Lion House, when the tiger, Tatiana, reached through her cage's iron bars and grabbed the keeper Friday afternoon," said Robert Jenkins, the zoo's director of animal care.

"We're still trying to figure out what happened and why it happened," Jenkins said.

"My understanding is the injuries are not life-threatening, but perhaps limb-threatening," said Fire Chief Joanne Hayes-White.

The animal keeper has been working at the zoo since 1997.

"Her main job is taking care of the zoo's four lions and three tigers," Jenkins said.

The attack took place during a regular 2 p.m. public feeding, during which keepers typically deliver a meal of horse meat through a small slot.

"No matter how familiar you get with these animals, they're still wild animals," Jenkins said.

"You have to have a healthy respect for them and be aware of what can happen."

The 3-year-old tiger arrived at the San Francisco Zoo from the Denver Zoo more than a year ago.

"There were no previous incidents of aggression against humans involving Tatiana," said Ana Bowie, a Denver Zoo spokeswoman.

"The mauling was the first attack of its kind against a human at San Francisco Zoo," Jenkins said.

Investigations are being made to see what triggered the attack.

San Francisco Zoo is one of the few zoos in the U.S. where big cats' feeding can be watched.

In another recent incident, a Sumatran tiger, an extremely endangered tiger subspecies (fewer than 500 specimens are left in the wild in the Indonesian island of Sumatra), destroyed a heat-sensitive surveillance camera.

The cat was frightened by the camera's flash and attacked the camera.

"Loggers, poachers and other wildlife have destroyed cameras in the past, but this was the first time the vandal had been positively identified," said a WWF spokesman.