Edmonton police spokeswoman Lisa Sobchyshyn said zoo staff arrived Wednesday morning to find about 65 dead guinea pigs scattered about the exhibit surrounded by oranges investigators think contained an unidentified poison, the Globe and Mail reported Thursday.
Sobchyshyn said the apparent poisonings occurred sometime after the zoo closed Tuesday. She said toxicology tests to confirm how the animals died would take some time.
The zoo exhibit does not have security cameras, the newspaper said.
"This is a very unusual incident, and police are not aware of any similar incidents," Sobchyshyn said.