Four mule deer, similar to these in Colorado, died at the Calgary Zoo between September and December of last year. (Nathan Bilow/Associated Press)

The Calgary Zoo says four deer that died at the zoo did not die because of human error, contrary to claims made Monday by the group Zoocheck.

The animals died over the course of several months last year, not over the last week, as claimed by Zoocheck in information sent to media outlets Monday. The group said a zoo employee reported that four mule deer died as they were being rounded up.

"This is not the case and this is not true," said Calgary Zoo spokesman Simon Scott.

"We had no incident involving mule deer last week nor any incident involving human error and mule deer last week."

Four mule deer did die at the zoo between September and December of last year, said Scott.

One animal was 13 years old and had pneumonia, another was being treated for an abscess, a third ran into a fence and the fourth deer was found dead by keepers when they came to work in the morning.

The Calgary Zoo is about to start an independent review of its animal practices after a number of animals died at the zoo including stingrays, and a wild goat that died after getting entangled in a toy a year ago.