FOSTER CITY, CALIFORNIA (NYTIMES) - They poop on the lawn. They poop in the park. That poop makes its way into the waterways. Officials in one California city have decided that enough is enough.

In Foster City, as in much of the United States, the Canada goose population is booming, and the birds are making a mess. Now the city is saying it may have no choice but to cull them in an attempt to reduce potential risks to the public from the birds' faeces.

"We all learn to be tolerant and to coexist with the wildlife, but lately we have been uncovering health hazards," said Ms Richa Awasthi, mayor of Foster City, which winds around a lagoon about 22 miles south of San Francisco.

She said the poop is "everywhere".

The proposal, however, has upset some residents and animal welfare activists, who fear that the city will round up the birds and euthanise them. Last month, demonstrators let out a rallying cry at a protest: "Let the geese live."

Thousands have signed a petition calling for a more humane solution. "Any method where they're not in pain, go for it," said Mr Erik Allen, 37, who lives in San Rafael, about 40 miles north of Foster City, and who organised the demonstration.

"People just need to understand that animals do the same things that we do," he said of the goose's corporeal functions. "Step over it. Care less."

Foster City has emerged as the latest battleground in America's war against Canada geese, one that is being waged largely because efforts to save the species have succeeded beyond expectations.

The Migratory Bird Treaty Act of 1918 set the birds on a path from the brink of extinction. By the late 1960s, however, the population had again dwindled, prompting programs such as Operation Mother Goose, in which wildlife officials carefully relocated fragile nests and eggs to safer habitats, sometimes by helicopter.

There are now millions of resident - or non-migratory - Canada geese in the United States, according to the Agriculture Department.

The rehabilitation programs were "far too successful," said Philip Whitford, a professor emeritus of biology at Capital University in Columbus, Ohio.

Resident Canada geese, he said, prefer short, fertilised grass and easily accessible bodies of water. In many US cities, he said, "we've created the perfect circumstances for them".