CALGARY - Staff at the Calgary Zoo were surprised to discover a 10-year-old Siberian tiger had given birth to two cubs.
They say the tiger named Katja had shown no outward signs of pregnancy.
Sadly, one of the cubs died shortly after birth.
Staff are working around the clock to care for the other cub at the zoo's animal health centre, noting the baby tiger is "struggling."
Katja was paired with a nine-year-old male tiger, named Baikal, from New York's Bronx Zoo last January as part of the zoo's Species Survival Plan.
Staff say if the cub recovers well, it will be returned to Katja as soon as possible.
"While it is generally preferable to keep hands-off and let the mothers raise their young without interference, obviously in this case with the cub in distress, that has not been possible," said zoo spokesman Tim Sinclair-Smith.
"We hope to place the cub back with Katja, realizing that there are inherent risks involved in the reintroduction of cubs back with their mothers and will work with industry experts for guidance to ensure all is taken into consideration."
Tigers can give birth over a period of several days so while it appears unlikely at this time, it is possible that there still could be more cubs born.
Siberian tigers are considered endangered and the population continues to decline. Census estimates indicate there are fewer than 400 adult/sub-adult Siberian tigers remaining in the wild.
"Both Katja and Baikal are considered very genetically valuable in the captive population so the fact that breeding was successful is positive from a species survival perspective," said Sinclair-Smith.
"However, we are always aware things can still go wrong in spite of our best efforts. Inexperienced mothers can sometimes be too aggressive or cubs may have health issues that are not apparent immediately."
One of the reasons that the zoo was surprised at the birth is that soon after Baikal's arrival they learned that in spite of a clear interest in breeding with Katja, he was having significant difficulty as a result of painful arthritic hips.
Zoo veterinarians say they're pleased that surgery performed at the end of May to reduce the pain in Baikal's hips has proven successful.
"We had performed a similar surgery with another male tiger, Lashka, which resulted in the birth of Vitali three years ago so we were optimistic that this procedure could also help Baikal," explained head veterinarian, Dr. Sandie Black.