The death of four baby blue penguins from nothing but "human stupidity" has broken the heart of Mauao Area Wildlife Trust chairwoman Julia Graham.

Mrs Graham monitors the penguins on Moturiki (Leisure) Island but has noticed an alarming increase of people drinking on the liquor-free island late at night and trashing the environment.

Two young penguins were trapped and starved to death because empty beer bottles were shoved into the entrance of their burrow, she said.

"The burrow was completely blocked off so the parents couldn't get to their babies to feed them."

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Another two healthy eggs were abandoned by their parents after increasing activity around their burrow.

"The main problem is people drinking there at night. One, we have a lot of nocturnal animals there and you may not realise you've parked yourself right in front of a burrow.

"You're actually stopping that bird from being able to get out to feed their babies. Even two hours could mean life or death for a young bird," she said.

"Two, once they've had a few drinks they're more likely to leave their bottles around and they'll go off trashing the island, swinging off trees and breaking branches."

"The damage that gets done is just horrific.

"It's not good. I cried, I cried like a baby. It breaks my heart."

Summer was a particularly problematic time, she said.

"The rubbish that gets left behind is just terrible. This time of the year the [human] population increases so you're going to get a lot more rubbish."

The trust would be increasing nightly patrols of the area for the summer period, she said.

"We don't want to be like this but we feel like it's the only way to get our point through."

She was thinking of the future, hoping in years to come she would take her grandchildren to Moturiki Island and the little blue penguins would still be there.

"Go, enjoy it, it's a beautiful place ... It's special and unique. We should love and cherish it."