The High Park Zoo is investigating what caused the sudden death of one of its bison.

The zoo was temporarily closed Saturday after the17-year-old bison named Alberta died, according to Toronto Parks and Recreation department spokesperson Matthew Cutler.

“The death was unexpected,” Cutler told CP24 on Saturday.

Toronto Counc. Sarah Doucette said Sunday that Alberta had been part of the herd for many years, along with the other three bison.

“They are family so we were shocked yesterday when we heard she had died,” she said.

Officials will be looking into the cause of death, according to the city’s Parks and Recreation department. In a written statement, they said that Alberta had “no recent history of illness” and that “staff were alerted to the death by zoo visitors who reported it to 311.”

The other bison were moved to another pen while workers moved the body.

The bison have been crowd favourites at the zoo because they walk right up to the fence.

“They like people. They want to watch you as much as you want to watch them. They have access to a big field in the back but usually they prefer to be at the front watching people,” Doucette said.

The three remaining bison are now back in their proper pen.