Since early November, keepers at Tierpark Berlin have been checking the polar bear den every morning on a surveillance monitor before entering the bears’ indoor area. At around eight o’clock in the morning of Thursday, 7 December, keeper Detlef Balkow got an early Christmas surprise: next to mother Tonja lay a tiny cub the size of a guinea pig. After last year’s arrival Fritz, who sadly died unexpectedly before venturing into the outside world, this is the second cub born to eight-year-old Tonja and six-year-old Wolodja. While visitors can still see daddy Wolodja in the outdoor area, mother Tonja and her cub are hidden away in the birthing den that she retreated to almost two months ago on 17 October.
“Naturally, we are delighted. But, just like last year, we now have to keep our fingers crossed,” reports Zoo and Tierpark Director Dr Andreas Knieriem. “The mortality rate for young polar bears is around 50 percent, and it is particularly high in the first ten days.” Even once this critical phase is over, the cub’s survival is by no means guaranteed. When watching surveillance camera footage from the previous night, keepers discovered that Tonja had in fact given birth to two cubs – but the first was stillborn and only visible for a brief time.
Polar bear curator Dr Florian Sicks is also very excited: “Tonja had been noticeably calmer since Tuesday. Then yesterday there was suddenly something tiny by her side. Today, I could even hear suckling noises as the cub was feeding.” With the careful rearing of her first young last year, Tonja showed that she has good maternal instincts and feels comfortable and safe in her birthing den.
Tonja and the cub’s father Wolodja mated several times in May and June. The exact gestation period of a polar bear is not known. The embryo begins to develop from the fertilised egg once the summer is over, following a period of “dormancy”. Like polar bears in the wild, females in zoos withdraw in the autumn to have their babies. The cubs are born when they are only about 30 cm in size and are still deaf and blind.
Over the coming days, no one will approach the birthing den. Mother and cub require total peace and privacy to give them the greatest chance of success. Following her maternal instincts, Tonja put on enough fat reserves to live off during this time.
Polar bear mother and cub are not currently visible to Tierpark visitors. Much like in the wild, the mother will not emerge from the birthing cave with her cub until spring.
Background:
Polar bears at Tierpark Berlin:
Tonja was born on 14 November 2009 at Moscow Zoo.
Wolodja was born on 27 November 2011 and originates from the other Moscow Zoo breeding group.
Polar bear births at Tierpark Berlin:
The first polar bear to be born at Tierpark Berlin arrived on 7 November 1986. The cub shared a birthday with the incumbent Tierpark director Heinrich Dathe, and was therefore named Björn-Heinrich. Björn-Heinrich died on 30 June 2011 at Palić Zoo in Serbia, having fathered three offspring.
On 3 November 2016, the Tierpark’s first polar bear cub in 22 years was born. Little Fritz achieved nationwide fame before he and his mother Tonja had even left the birthing den. He died aged just three months on 7 March 2017. Despite numerous tests carried out by a number of veterinary pathologists, human pathologists and toxicologists, the precise cause of Fritz’s sudden death remains unknown. However, examinations are still ongoing.
To date, a total of eight polar bear cubs have been born at Tierpark Berlin to four different mothers. All but one of those cubs were raised by the mothers; the other was hand-reared.
