KNUT, the Berlin Zoo's well-known polar bear, may soon have as many as three little siblings before Christmas, the zoo's veterinarian said Friday.

Knut's mother, Tosca, and the zoo's two other female polar bears, Katjuscha and Nancy, may all be pregnant after mating earlier this year with Knut's father, Lars, veterinarian Andre Schuele said.

They could give birth before the end of December, he said.

But polar bear pregnancies are hard to detect and to track. Tests like those humans use do not work, and polar bear embryos are so small the mothers do not grow big tummies.

"One can't say for sure if they are really pregnant or not," Schuele said.

The zoo is hopeful enough, however, to have built three special caves for the female polar bears to use to give birth.

Knut, who celebrates his first birthday Dec. 5, was rejected by his mother after birth and hand-raised by zookeepers. So potent was the cute cub's appeal that zoo attendance went up by 20 percent since his public debut in March, officials said. He has his own blog and TV show and appeared on the cover of Vanity Fair, not to mention scores of German newspapers and other publications.

Now weighing more than 100 kg, the boisterous bear no longer plays with his keeper Thomas Doerflein and has an enclosure all to himself.

(SD-Agencies)