Dozens of brown pelicans have been attacked and had their wings snapped in California, and now authorities are investigating whether the culprit is human.

Officials say that more than 30 injured birds have been found along the Orange County coastline since last October.

And, of those, 22 were suffering from compound fractures with the broken bone sticking out of the skin, according to the Wetlands and Wildlife Care Center of Orange County.

All 22 of the birds have had to be euthanised.

“These are very serious injuries that require emergency surgeries and long term care,” said veterinarian Elizabeth Wood.

“One pelican went straight into emergency surgery to flush out all of the debris in the open wound,” said Ms Wood.

“So bone was protruding through the skin, and the wing was actually twisted all the way around.”

She added that she does not know for certain that the injuries were caused deliberately, but that the humerus bone of the bird takes “significant force to break”.

“At this point we don’t have any suspects, we don’t have witnesses, we don’t have evidence other than the injured birds,” Captain Patrick Foy of the state’s Fish and Wildlife’s law enforcement division told The Los Angeles Times.

“If there is a person catching these pelicans and intentionally releasing them injured, how are they even catching them?... And from there, what would be the motivation of a person that has injured the birds?”

He added that officials from the Care Center had been provided a tip that suggested a specific individual was involved, but that he could not elaborate on an active investigation.

And he said that investigating the pelican injuries “is a priority issue” and is encouraging the public to contact Fish and Wildlife with information.

“Everyone has become aware of this and is paying attention,” he said.

Caring for a pelican with an open fracture takes months of therapy and can cost between $50,000 and $100,000.

Brown pelicans, which are not a threatened or endangered species, winter in California and are protected under the Migratory Bird Treaty Act.