SAN DIEGO >> A federal court is being asked to grant constitutional rights to five killer whales who perform at marine parks — an unprecedented and perhaps quixotic legal action that is nonetheless likely to stoke an ongoing, intense debate at America’s law schools over expansion of animal rights.

People for the Ethical Treatment of Animals is accusing the SeaWorld parks of keeping five star-performer whales in conditions that violate the 13th Amendment ban on slavery. SeaWorld depicted the suit as baseless.

The chances of the suit succeeding are slim, according to legal experts not involved in the case; any judge who hews to the original intent of the authors of the amendment is unlikely to find that they wanted to protect animals. But PETA relishes engaging in the court of public opinion, as evidenced by its provocative anti-fur and pro-vegan campaigns.

The suit, which PETA says it will file Wednesday in U.S. District Court in San Diego, hinges on the fact that the 13th Amendment, while prohibiting slavery and involuntary servitude, does not specify that only humans can be victims.

Jeff Kerr, PETA’s general counsel, says his five-member legal team — which spent 18 months preparing the case — believes it’s the first federal court suit seeking constitutional rights for members of an animal species.

The plaintiffs are the five orcas, Tilikum and Katina based at SeaWorld in Orlando, Fla., and Corky, Kasatka and Ulises at SeaWorld San Diego. Tilikum, a six-ton male, made national news in February 2010 when he grabbed a trainer at the close of a performance and dragged her underwater until she drowned.

Captured nearly 30 years ago off Iceland, Tilikum has enormous value as a stud and has fathered many of the calves born at SeaWorld parks.

The lawsuit asks the court to order the orcas released to the custody of a legal guardian who would find a "suitable habitat" for them.

"By any definition, these orcas are slaves — kidnapped from their homes, kept confined, denied everything that’s natural to them and forced to perform tricks for SeaWorld’s profit," said Kerr. "The males have their sperm collected, the females are artificially inseminated and forced to bear young which are sometimes shipped to away."

SeaWorld said any effort to extend the 13th Amendment’s protections beyond humans "is baseless and in many ways offensive."

"SeaWorld is among the world’s most respected zoological institutions," the company said. "There is no higher priority than the welfare of the animals entrusted to our care and no facility sets higher standards in husbandry, veterinary care and enrichment."

The statement outlined the many laws and regulations SeaWorld is obliged to follow, touted the company’s global efforts to promote conservation of marine mammals, and said the orcas’ performances help give the public a better appreciation and understanding of these animals.

SeaWorld and other U.S. marine parks are governed by the Marine Mammals Protection Act, which allows public displays of the creatures if permits are obtained and the facility offers and education/conservation programs for the public.

Overall, under prevailing U.S. legal doctrine, animals under human control are considered property, not entities with legal standing of their own. They are afforded some protections through animal-cruelty laws, endangered-species regulations and the federal Animal Welfare Act, but are not endowed with a distinct set of rights.

However, the field of animal law has evolved steadily, with courses taught at scores of law schools. Many prominent lawyers and academics have joined in serious discussion about expanding animal rights.

Rutgers University law professor Gary Francione, for example, contends that animals deserve the fundamental right to not be treated as property. Law professor David Favre of Michigan State University has proposed a new legal category called "living property" as a step toward providing rights for some animals.

Favre was skeptical that litigation seeking to apply the 13th Amendment to animals would prevail.

"The court will most likely not even get to the merits of the case, and find that the plaintiffs do not have standing to file the lawsuit at all," he said by email. "I also think a court would not be predisposed to open up that box with fully unknown consequences."

Harvard law professor Laurence Tribe, who in past writings has proposed extending legal standing to chimpanzees, also expressed doubt that the courts were ready to apply the 13th Amendment to animals. But he welcomed the PETA lawsuit as a potentially valuable catalyst for "national reflection and deliberation" about humans’ treatment of animals.

"People may well look back at this lawsuit and see in it a perceptive glimpse into a future of greater compassion for species other than our own," Tribe wrote in an email.

Tribe noted that some Americans might find it bizarre or insulting to equate any treatment of animals to the sufferings of human slavery. But he argued that the 13th Amendment was written broadly, to address unforeseen circumstances, and could legitimately be applied to animals.

An African-American constitutional expert, Nicholas Johnson of Fordham University School of Law, said he could understand why some blacks might be insulted by the lawsuit, but didn’t share that reaction: "I’m more entertained by it in the legal context than I am offended by it."

PETA addressed this issue in the suit, noting that repeated Supreme Court rulings have applied the 13th Amendment to many forms of involuntary servitude beyond the type of slavery that existed during the Civil War.

"The historical context is undeniable," said Jeff Kerr, the PETA lawyer. "But that’s not what this case is about. It’s about the orcas in their own right, not whether they are or aren’t similar to humans."

The five orcas are represented in the case by PETA and four individuals: Ric O’Barry, a longtime orca and dolphin trainer; Ingrid Visser, a New Zealand marine biologist who has studied orcas extensively; Howard Garrett, founder of the Orca Network, an advocacy group in Washington State; and Samantha Berg, a former orca trainer at SeaWorld Orlando.

The lawsuit details the distinctive traits of orcas, the largest species within the dolphin family, including their sophisticated problem-solving and communicative abilities and their formation of complex communities.

The suit alleges that captivity in the "barren tanks" of a marine park suppresses the orcas’ abilities and relationships, and subjects them to stress. This sometimes leads to instances where the orcas injure themselves, other orcas or humans that interact with them, according to the suit.

Naomi Rose, the Humane Society’s marine mammal biologist, said there’s a growing body of research suggesting that whales, dolphins and porpoises have the cognitive sophistication of 3-to-4-year-old human children.

As for the orcas at SeaWorld, she said, "They don’t seem to adapt to captivity. I would say they’re miserable."

At SeaWorld San Diego, visitors are shown a film touting the park’s rescue efforts that have saved thousands of sea creatures. During the main performance, trainers point out how much the orcas are similar to humans: The babies cry before moving on to babbling and finally imitating the crackling sounds of the adults’ voices.

Jenny Raymond, 47, who was visiting from Switzerland, said she was delighted by the show and does not buy the argument that the orcas are slave laborers.

"I think they are in better conditions here than in the wild," she said.

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David Crary reported from New York City.