Penguins are susceptible to stress and were badly affected by the incident
A dozen penguins at a sea life centre are being given special care after a youth vaulted the perimeter fence and chased the birds in the dead of night.
Keepers at Scarborough's Sea Life Centre were alerted to the intruder when his movements were picked up by CCTV cameras focused on the penguins.
He was seen chasing the birds around their pen for 15 minutes.
Centre manager Hayley Townsend said the penguins suffered badly from stress and described the attack as "heartless".
Ms Townsend said specialist keepers were watching the birds closely to see if they needed medication to alleviate stress after the ordeal.
She said: "CCTV pictures showed he was in the enclosure and he was in there for about 15 minutes.
"The birds are very susceptible to stress and we're having to keep them under quite close observation."
She said the intruder had climbed over a perimeter fence and then jumped into the birds' pen.
"We can't believe how irresponsible and heartless some people can be.
"It really is a shame that some people do this kind of thing."