Officials with the Calgary Zoo are saddened by the loss of two hippopotamus calves that arrived stillborn on Friday afternoon.

Sparky, the zoo’s 26-year-old hippo, delivered stillborn twin calves on January 3, 2014. Calgary Zoo staff attempted to resuscitate the nearly full term hippo fetuses but their efforts were in vain.

A necropsy on the calves determined the loss of the two hippos was likely the result of entangled or twisted umbilical cords.

Sparky’s pregnancy caught zoo officials by surprise.

"Sparky has been on birth control for a number of years," said Colleen Baird, Calgary Zoo Curator. "We were becoming suspicious that she was pregnant because of recent weight gain and some behavioural changes, but we thought it wasn't possible given the birth control measures in place combined with her senior age and Lobi‘s immaturity (the zoo’s male hippo). It appears nature had other ideas."

Sparky was born in May of 1987 in Toronto and has been a fixture of the Calgary Zoo since her arrival in September of 1988.