Two zebras can be seen in their enclosure at the Greater Vancouver Zoo in this undated photo. (CBC)

The Greater Vancouver Zoo is calling the sudden death of four zebras two months ago a freak accident nobody could have predicted or prevented.

The zebras died within days of each other after two Cape buffalo were added to their enclosure, officials said.

The general manager of the privately run zoo, Jamie Dorgan, said zebras and Cape buffalo naturally coexist in the wild and the zebra's panicked reaction was unpredictable.

"It was one of those freak type of situations unfortunately. After the fact, discussing with other zoo experts and people, hardly anyone believes things went the way they went. It was totally unexpected and I don't think we could repeat it if we wanted to," Dorgan said.

The British Columbia Society for the Prevention of Cruelty to Animals has opened an investigation of the case, but a spokesman said Tuesday it could take weeks to complete.

"It could take weeks, it could take months before we get the information presented to Crown," said Shawn Eckles, chief animal protection officer with the SPCA.

"Hopefully it won't be that long, and hopefully we'll have some sort of a resolution with respect to our investigation within the next couple of weeks," he said.

Eckles said all the society can do is investigate complaints and, where appropriate, recommend charges to the Crown.

Prior criticism raises concerns

Vancouver Humane Society spokesman Peter Fricker said Monday that he suspected the zebras likely suffered from exertional myopathy, a muscle disease characterized by damage to muscle tissues brought about by physiological changes, usually following extreme exertion, struggle and/or stress.

Fricker said Cape buffalo are extremely dangerous animals and, although zebras and buffalo co-exist in the wild, putting them together in an enclosed space was a mistake.

The zoo has faced much criticism over the years about how its animals are housed, but Dorgan is confident inspectors will find no evidence of cruelty or neglect.

The zoo recently had its accreditation with the Canadian Association of Zoos and Aquariums reinstated after it lost its accreditation following a prior animal welfare controversy.

Last spring the zoo, which is located in Aldergrove east of Vancouver, was in the news after thieves stole a spider monkey from an enclosure.

Before that, the zoo was criticized for having inadequate shelter for a young hippo, the death of a young giraffe, and the death of a hippo that fell through a frozen pond.