As a young boy, Mac Tileston used to shoot ring-necked pheasants in marshes around his family's Cape Cod house and at a special place in East Harwich known to be stocked by the state game warden especially for neighborhood kids.

Those days are long gone. Tileston, 49, will be out stalking the birds with his teenage daughter this fall, but in recent decades he has been restricted to fewer than 3,000 acres of land on an increasingly densely populated Cape. And now, Tileston faces the prospect that this season could be among his last.

Animal-protection groups have filed a lawsuit -- one of the first of its kind -- against the Interior Department to halt a nearly century-old tradition that involves trucking hundreds of pheasants onto the Cape Cod National Seashore. And while a federal judge recently declined to grant an injunction sought by the groups to block this year's hunting season, which opened Oct. 19, the National Park Service announced that it intends to phase out the program eventually.

The Humane Society and two other groups contend that the Cape Cod pheasant hunt is unethical, illegal and environmentally hazardous. They argue that it violates National Park Service management policies against introducing exotic species amid mounting concerns nationwide about such species threatening native animals and plants. The Cape's National Seashore is the only national park that allows stocking of non-native birds, Park Service officials said.

Hunting opponents also say importing the birds for recreational hunting, with no chance of independent survival, amounts to slaughter.

"There is no reason to breed these animals to be put through a short life of misery," said Michael Markarian, president of the Fund for Animals in Silver Spring, Md.

Federal policies permit stocking of non-native animals for recreational hunting in national recreation areas or preserves that have been historically stocked without harm to natural resources. But defenders of the hunt fear that the lawsuit, if successful, could set a legal precedent that would have implications for other states that introduce non-native species for recreational fishing or hunting, such as brown trout, rainbow trout and elk.

Sport hunters and their advocates argue that pheasant stocking is an important cultural and recreational tradition that does not endanger the environment or humans, and that, with its beginnings in 1906, the hunt predates the creation of the National Park Service in 1916 and the National Seashore in 1961.

Given the rapid development of the Cape's rural areas, Tileston and others say they have few other options.

"There's nowhere else left to hunt; that's what makes the National Seashore so important," he said. "It's really the last stronghold we have."

Ring-necked pheasants, with their distinctive band and fancy tails, are native to Asia and have been imported to the United States since the late 19th century.

These days, the state Division of Fisheries and Wildlife uses proceeds from hunting license fees to purchase 40,000 of the birds for $8 apiece from private game farms in the Northeast. The vast majority are trucked to state-owned land, but a total of 800 birds are released on six consecutive Friday nights in three areas of mostly scrub pine and oak within the Cape Cod National Seashore.

Critics of the program say the seashore should be protected from the introduction of non-native species, especially when parks nationwide are moving toward restoring native habitats and creating hunting programs that rely on breeding native animals.

"In other parks, you're getting rid of non-native species, and here you are introducing a non-native," said Jessica Almy, a wildlife advocate with the Humane Society's Cape Wildlife Center.

The Humane Society, the Fund for Animals and the Massachusetts Society for the Prevention of Cruelty to Animals allege in their lawsuit that hunters and their dogs hurt vegetation, frighten native animals and put visitors at risk of being shot. There are no documented incidents of injuries or fatalities related to pheasant hunting, park officials said, although one Cape resident who is party to the lawsuit alleged that her son was nearly shot by a hunter and another said his dog was almost killed.

Animal-protection advocates also cite concerns that non-native pheasants could threaten existing species by spreading disease or introducing antibiotic-resistant microorganisms after being given medicated feed in captivity.

Mark Pokras, director of the wildlife clinic at Tufts University's School of Veterinary Medicine in North Grafton, Mass., said it remained unclear whether the pheasants posed any disease threat. But he said there was no evidence to suggest that they were likely to become an invasive species or cause significant environmental damage for one simple reason: They die too fast.

Unlike Canada geese, whose population swelled after they were kept here to be used as live decoys, ring-necked pheasants do not appear to live through the winter. Hunters kill an estimated one-third of the birds during the hunting season, and the rest perish from starvation, predation or run-ins with cars.

"If they were going to become established and a problem species, they would have done so amply by now," Pokras said. "From the point of view of worrying about invasive species, we should probably put our time and efforts into something besides pheasants."

Kevin FitzGerald, chief ranger of the Cape Cod National Seashore, said the park's decision to phase out the pheasant hunt was part of a larger ongoing management plan to restore native habitat, such as grasslands and heath lands. The Park Service has not established a deadline for ending pheasant stocking, however. That concerns critics as well as hunters, who say they will continue to fight the challenge while making the most of their remaining days in the field.

"A lot of guys are saying, 'Am I going to be able to take my grandchildren out there?' " said Michael Veloza, president of the Barnstable County League of Sportsmen's Clubs. "Hopefully, we'll be able to keep the tradition going. We share the seashore with everyone."

Native to Asia, ring-necked pheasants have been brought to Cape Cod for hunting for almost 100 years, including a six-week bird season in the federal Cape Cod National Seashore.