Nicole Rivard, a spokesperson for Friends of Animals, said she and fellow members of the animal welfare organization believe mute swans shouldn’t be treated like vermin.

The birds arrived here through no fault of their own, brought by humans, and they don’t deserve to be killed for it, she said.

Rivard believes the California legislation is motivated by hunters looking for an excuse to have yet another bird to legally shoot. Currently, mute swans can only be killed by landowners if the birds “are found to be injuring growing crops or property,” according to state regulations.

“We’re anti-hunting, so we don’t like the idea that (hunting) might be, you know, part of the reasoning behind this,” Rivard said.

Arguing that claims of mute swans’ environmental damage and aggression are overblown, Friends of Animals and other groups opposed killing them decades ago, after Mid-Atlantic states proposed eradication when their populations began expanding dramatically in the 1990s and early 2000s.

The groups protested, filed lawsuits and proposed legislation to try to stop the killing. They had mixed success. Some states began killing the nonnative swans over the animal welfare groups’ objections. Notably, Maryland was able to knock the mute swan population down from around 5,000 birds in the early 2000s to around 200 by 2010.

“Continued control and maintenance operations have reduced that number to just a handful of birds today,” said Josh Homyack, the game bird section leader for the Maryland Department of Natural Resources.

In Maryland, government agency employees raided mute swan nests and destroyed eggs, captured and euthanized swans when they were flightless during their feather-molting season and shot them in carefully coordinated operations, Homyack said. The state also issued a few permits to kill the birds to local landowners.

In New York, the mute swan lobby got a law passed that made it harder to kill the birds, requiring state officials to “fully exhaust non-lethal control measures” such as nest destruction and capturing birds and moving them to wildlife facilities “prior to any lethal removal.”

The mute swan population in New York has stayed steady at around 2,000 to 3,400 birds.

Charisma matters with invasive species

On the East Coast, mute swans have been around since before the turn of the last century. They were first imported as ornamental livestock for zoos, parks and estates.

Some of California’s mute swans likely came in the same way. Weaver, the California waterfowl coordinator, said others were likely brought in the past few years to chase away Canada geese that have increasingly become a nuisance at parks and golf courses.

“People were buying these (swans), and they were just throwing them out there,” she said.

Weaver noted their owners didn’t do the responsible thing and clip their wings to keep them from flying off. That’s hardly surprising. It’s no easy task to grab a hissing 25-pound swan, big and angry enough to swamp a kayaker. So with nothing to stop them, the birds flew to nearby marshlands and began reproducing.

“Here we are, not very many years down the road, with a population that is really increasing at a rapid rate,” Weaver said.

So far, California’s wildlife agency hasn’t enacted a mute swan eradication plan similar to the one it started almost immediately – and publicly promoted – a few years ago, after nutria first started turning up in the San Joaquin Valley.

Nutria are similarly destructive feeders on aquatic plants. The South American swamp rodents also burrow holes in levees, posing a threat to the state’s flood-control and water-supply infrastructure.

Dave Strayer, a retired invasive species expert with the Cary Institute of Ecosystem Studies in New York, said he’s not surprised state officials haven’t been as aggressive with the beautiful mute swans, given the uproar over killing them in other states.

He said research has shown that when it comes to invasive animals, charisma matters. The more attractive a problematic non-native species is, the less appetite there is to wipe it out.

Stayer gave an example: Few complain about killing common nonnative rats, but you’re apt to get death threats at even the suggestion of wiping out ecologically harmful feral cat colonies in the same habitats.

He noted that no one has ever complained about efforts to eradicate one of his research subjects, the nonnative zebra mussels that have also invaded California.

“I never had even one person stand up for zebra mussels and say, ‘No, these are beautiful, elegant God’s creatures’ and so forth,” he said.

Few wetlands and too many mute swans

Supporters of the swan-killing legislation say reducing the number of mute swans should be fairly easy since the giant white birds are easy to spot, identify and kill. Their size and the color and shape of their bills also reduce the risk they’ll be confused with other protected bird species, they say.

California’s native tundra and trumpeter swans would still be protected and illegal to shoot if the bill becomes law.

Despite their undeniable beauty, Weaver, the state waterfowl coordinator, sees mute swans similarly to nutria.

The swans pose too great a threat to native species reliant on the few wetlands left in California, which has lost at least 90% of the habitats to agriculture and urban sprawl.

“They don’t move around the state all that much, and they really like the Delta-Suisun Marsh area, so it’s still easy to handle the issue,” Weaver said. “The longer we wait, it won’t be.”