An elderly bison died unexpectedly at High Park Zoo on Saturday, launching a city investigation amid some sharp criticism online about how the zoo handled the animal's death.

Known as Alberta, she was one of four bison living in the zoo's enclosure. While the zoo did not provide her exact age when she died, she was considered elderly by bison standards. The formidable animals typically live to about 20 if they survive into adulthood.

While old, Alberta was considered healthy and her death took zookeepers by surprise.

"The animal had no recent history of illness, the death was unexpected," said Matthew Cutler, spokesperson for Toronto parks, forestry and recreation, in an email.

Zoo staff were alerted to Alberta's death by multiple calls to 311 from park visitors. One of those witnesses, Chantrey Gribben, took a photo of the dead animal and posted it to Facebook.

"People were whispering, so their kids couldn't hear them, 'I think he's dead'," Gribben told CBC Toronto. "Its legs were protruding straight, it had already kind of gotten stiff."

She adds that fluids were visibly leaking from the bison's orifices, and that the zoo's youngest bison kept trying to lie beside Alberta until others in the herd shuffled the little one away.

'Nobody was coming by'

Gribben said she called the city at around 3 p.m. She was told that animal services would be immediately contacted. Another couple also made calls of their own.

"We figured the more people that call, they'll take it pretty seriously and get here faster. And an hour went by, then an hour and a half went by," she explains.

"So I called animal services and they said 'no, we've had no phone call about this, we haven't been notified yet.'"

It's not a good look for the city. For tourists coming in and that's what they see in our zoo? - Chantrey Gribben, High Park Zoo visitor

More than two hours after the initial calls, Alberta was still lying in the late afternoon heat. Gribben and her partner then tried to find zoo staff, she said.

"We were shocked that no staff had come by. We thought that maybe every few hours maybe staff would come by and make sure the animals are okay," she said. "But nobody was coming by."

'This is a family'

Toronto city councillor Sarah Doucette told CBC Toronto, however, that Gribben's Facebook post and subsequent dialogues in the comments exaggerated the circumstances of Alberta's death and spread "information that wasn't quite accurate."

"I would not call it a decomposing body, definitely not," said Doucette, also a member of the Friends of High Park Zoo board.

Zookeepers visit the bison multiple times each day and all of the zoo's animals are cared for well, she added.

Despite visitor concerns that Alberta was the young bison's mother, Doucette said she has confirmed that the mother is in fact Victoria, the zoo's other adult female. If the bison seemed distress, it was due to a "herd mentality."

"They'll be sad. This is a herd. This is a family. They've been together a long time," she said. "It's a tragic loss."

'Not normal'

The zoo closed early on Saturday so staff could remove Alberta's remains, but reopened Sunday morning when High Park opened for the day.

Once the zoo has more details about the animal, it will share with them with the public, Cutler said in his email.

The zoo, located inside High Park on Deer Pen Road, also has deer, llamas, peacocks, highland cattle and capybaras.

Gribben said the experience has left her with lingering questions about the welfare of the zoo's animals.

"A dead animal on display at a zoo is not normal," she said. "It's not a good look for the city. For tourists coming in and that's what they see in our zoo?"