Toronto zoo polar bear cubs die after being born underweight TORONTO, Dec. 11 (UPI) -- Two polar bear cubs born in the Toronto zoo have died just days after their birth, though veterinarians don't know exactly why. The cubs, born underweight and underdeveloped late last week, seemed to be doing well with care from their mother, Aurora. A third cub died shortly after birth, zookeepers told the Toronto Star Monday. The two surviving cubs each weighed about 1.5 pounds and died Sunday. Aurora has been a mainstay attraction at the Toronto zoo since 2001, when she was brought there after being found wandering along with her sister, Nikita, after a poacher killed their mother in a provincial park near Hudson Bay. Aurora attacked her last litter of cubs. Zoologists were encouraged when Aurora tended to her cubs this time around. "The fact that Aurora was doing everything right this time is a huge step in the right direction," said Maria Franke, curator of mammals at the Scarborough zoo in a press release. Given that [the] polar bear cubs were born so small and undeveloped, there are many possibilities of what could have happened.