Bill Merkle presses a button on his remote control, and the “ooh ooh ahoo” of an adult barred owl spills out of a black speaker and ricochets through the canyon at the heart of Muir Woods in California. Moments later, three fluffy fledgling barred owls alight nearby and start screeching for food.

Visitors to the Marin County redwood grove stop to snap photos, awed at seeing the football-size raptors during daylight hours.

But Merkle, a wildlife ecologist for the National Park Service, isn’t quite as pleased. After elbowing native northern spotted owls out of Washington, Oregon and other parts of Northern California, invasive barred owls have gained a critical foothold in Muir Woods, the southernmost domain of its imperiled spotted cousin.

As in other cases where newcomers displace indigenous species, federal wildlife regulators on the West Coast are struggling with how to manage this new threat to ensure that the underdog doesn’t die out.

“We’re not talking about extirpating the barred owls,” said Robin Bown, biologist with the U.S. Fish and Wildlife Service in Portland, Ore. “But our hope is that we can create a niche for the spotted owls that they can protect and that the barred owls don’t use.”

This fall, Bown’s agency will lay out a plan to eliminate barred owls from a handful of spotted owl territories to study whether the spotted owls rebound. But there’s a catch. One of the potential removal methods involves shooting the barred owls. In scientific parlance, it’s called “on-site lethal removal.”

The study sites and number of owls to be removed haven’t been decided yet, Bown said. The agency will also evaluate the “do nothing” option as well as a capture-and-release program.

Any mention of the shooting strategy, however, is bound to stoke controversy in conservation circles. For one, “shooting a charismatic raptor is always a difficult idea,” Bown acknowledges.

On top of that, it’s unclear whether eradicating pockets of barred owls will boost a spotted owl population in free fall, not to mention the money and time involved in ongoing removals.

Bown said those are the kinds of questions the study hopes to answer.

Nevertheless, some environmental groups doubt the wisdom of any species removal in an area with few clear boundaries. Wiping out a nonnative animal on an island makes sense, said Golden Gate Audubon Society’s Mike Lynes, because it’s a discrete land mass difficult for an invader to repopulate.

On the mainland, “we see more mixed results when, for example, common ravens are removed because they prey upon snowy plovers,” said Lynes, the group’s conservation director. “It may provide short-term relief over a breeding season, but new ravens just move in.”

Based on observations, five or six barred owls hunt and nest in the shade and cool of Muir Woods — three or four fledglings and their parents. Plus another adult pair in Olema Valley in western Marin.

That’s a small number compared with the 120 to 140 northern spotted owls in Marin County, Merkle said.

If history is any teacher, however, those numbers will start to reverse. Whereas northern spotted owls are smaller, less prolific and prefer a diet of dusky-footed wood rats, barred owls are bigger, more aggressive, bear more young and will eat just about anything, from crayfish and insects to mice and smaller birds.

Because Marin County has the densest population of northern spotted owls in the country and Muir Woods represents the southernmost edge of its range, scientists are particularly worried about the impact of the barred owl.

“Our concern is that the (barred owl) population will hit a tipping point and take off,” Merkle said. “In areas where barred owls have a longer history and larger population, it’s shown that they outcompete spotted owls.”

Barred owls are just the latest menace to a species that has been embroiled in controversy for decades.

.Back in the late 1980s, grave concerns about habitat loss and the logging of old-growth forests landed the northern spotted owl on the federal endangered species list and closed off millions of acres to timber harvesting. The move set off a firestorm, with critics protesting the protection of a dwindling bird species at the price of thousands of logging jobs and millions in revenue.

Despite the curbs on timber harvesting, though, the species has continued to tumble — up to 40 or 50 percent in parts of Oregon. Sudden oak death is also thought to be a culprit because it kills trees within the lush understory of many old-growth forests. Only in the past decade did scientists shift their focus to barred owls, which began migrating from their original habitats in the East and Midwest after 1900.

Experts in Washington and Oregon first saw the brown and white raptors — which are strikingly similar to northern spotted owls aside from more vertically oriented white stripes on their breasts — in the 1960s and 1970s.

They didn’t arrive in Northern California and the Bay Area until much later.

The first one appeared in Muir Woods in 2002. Five years later, the first pair bred successfully. The next year, meanwhile, saw no northern spotted owl fledglings on federal or state parklands in Marin County, Merkle said.