The 10 Humboldt penguins dived into the water to escape and staff at Scarborough’s Sea Life Centre say the birds now can’t sleep and are reluctant to leave the pool.
They are being treated with a herbal remedy to calm them.
Displays Curator Lyndsey Crawford, 33, said: “Birds are extremely prone to stress. It can kill them. “I can’t understand why anyone would want to hurt them.”