Tierpark PM

An advent cub for Tonja

Tierpark Berlin’s polar bear gave birth on 1 December.

For the last few weeks, female polar bear Tonja has been sleeping up to 22 hours each day. But last Friday, she seemed rather agitated and slept much less. Then, at 2:33 a.m. on 1 December, Tonja finally gave birth to a teeny little cub the size of a guinea pig.

Thanks to sophisticated new camera technology, curator Dr Florian Sicks is able to monitor the birthing den around the clock – including from his home – and he was therefore the first to discover the new arrival. So far, the cub has been lying safe and warm on its mother’s thick fur. Dr Sicks was glad to hear suckling noises for a good long while at around 9 p.m. on the day of the birth. “That’s when I was able to relax a little,” he said. “Now the cub is drinking regularly, around every two to three hours.”   
Tonja mated with male polar bear Wolodja several times in March and April. Over the months that followed, she put on a good amount of winter fat. From a slender 230 kilos in March, Tonja weighed in at a hefty 390 kilos by September. While keepers suspected that the bear was pregnant, they were not able to confirm their hopes: “The polar bear is one of the most dangerous land carnivores in the world,” explains Dr Sicks. “We wouldn’t have been able to examine Tonja without administering general anaesthetic, which would have put her baby at risk.” The precise gestation period of polar bears is unknown. After fertilisation, a polar bear embryo remains in a suspended state until sometime during the summer, when it begins to develop. In the wild as well as in zoos, female polar bears retreat into dens in the autumn to bear their young.

“Over the last two years, we have had painful reminders of how quickly the joy at such news can dissipate,” says Zoo and Tierpark Director Dr Andreas Knieriem. “Infant mortality in polar bears is extremely high, especially within the first ten days of life. However, we are all staying positive and keeping our fingers crossed for Tonja. In the past, she has proved to be an excellent mother, and this time is no exception. Thanks to our new camera system I, too, am able to watch Tonja and her cub in the birthing den – live and from my own home!”

No one will approach the birthing den over the next few weeks. Absolute peace and quiet is essential for the successful rearing of young polar bears.

The polar bears are currently not on view to Tierpark visitors. In zoos just as in the wild, mothers and their cubs do not leave their dens until the spring.