A California federal court is to decide for the first time in US history whether amusement park animals are protected by the same constitutional rights as humans.

The case arises from a lawsuit filed by rights group People for the Ethical Treatment of Animals, often called Peta, on behalf of five orcas that perform water acrobatics at the SeaWorld amusement parks in San Diego and in Orlando, Florida.

The group argues that continuing the whales' "employment" at SeaWorld violates the 13th amendment to the US constitution, which prohibits slavery.

District Judge Jeffrey Miller heard arguments on Monday and reviewed the response from SeaWorld, which asked that the lawsuit be dismissed.

His ruling is expected to come later.

The suit, filed in October, asked that the court declare that the orcas are "held in slavery and/or involuntary servitude by defendants in violation of the 13th amendment to the US constitution".

"It's a new frontier in civil rights," said Jeff Kerr, Peta's general counsel, who described the hearing as a "historic day".

"Slavery does not depend on the species of the slave any more than it depends on race, gender or ethnicity.

"Coercion, degradation and subjugation characterise slavery and these orcas have endured all three."

The complaint says the five killer whales are represented by their "friends at Peta", who include three former whale trainers, a marine biologist and the founder of an organisation that seeks to protect orcas.

The complaint demands that the court "appoint a legal guardian to effectuate plaintiffs' transfer from the defendants' facilities to a suitable habitat in accordance with each plaintiff's individual needs and best interests".

SeaWorld's motion to have the case dismissed argues that the 13th amendment "protects only people, not animals, from slavery and involuntary servitude".

The courts lack authority to extend the amendment to animals, which could "open a veritable Pandora's box of inescapable problems and absurd consequences," it argued, denying any implications of cruelty to animals.