Staff arriving on Wednesday morning found several cages broken, glass strewn all over the floor, and two of their prize monkeys, Nano, a pygmy marmoset and Harald, a cotton-top tamarin, missing.
"They are social animals, and they need their group to thrive," Camilla Bjerke, the animals' keeper at Oslo Reptile Park, told TV2. "I cannot even imagine the stress they are now exposed to."
Most marmoset species measure no more than 20cm in height, making them popular pets. Keeping monkeys as pets in Norway is illegal, but in neighbouring Denmark, marmosets sell for up to 8000 kroner ($1000).
Bjerke fears that the monkeys may already be dead.
“Our monkeys are not used to being handled. They can handle people close by, but not being petted or held," she said. "Monkeys are fragile animals and new surroundings can be very frightening. The ones that remain in the park are very frightened and have not come out all day.”
The Oslo police are investigating the incident and Bjerke hopes that the monkeys can be recovered in good health.
“We are taking this case very seriously. This is about animal welfare,” Ole Rasmus Knudsen of the Oslo police told NRK.
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Bjerke is now appealing to the public to bring the monkeys Nano and Harald home.
“Call us. Put the monkeys outside. Give them to someone who can give them back. We just want our monkeys back,” she said to TV2. “The monkeys live in a group. They are stressed and it may kill them. The pack is safety for animals like this.”