On a sunny day in Denver, parks overflow with residents enjoying the outdoors. But more and more people also are finding themselves co-existing with the large amounts of geese who call the parks home — and the slimy, green poop they leave in their stead.

Following the creation of the Migratory Bird Treaty Act of 1918, many Denver parks, including Washington Park and City Park, began experiencing an overabundance of Canada geese. The U.S. Department of the Interior drafted the legislation to protect an endangered migratory species of Canada geese — not the resident ones.

That distinction that has become the crux of a dispute surrounding the waterfowl: Conflicts involving wildlife and people seem to elicit passionate and spirited opinions from both sides of the issue.

“I have lived in South City Park for 30 years and I believe the geese have a right to be here,” said Bonita Lahey. “They are protected by international law.”

David Scarbeary, also a 30-year resident of City Park South, finds the volume of goose excrement unacceptable. He laments cleaning goose poop from his dog, as well as himself. He also feels the geese are responsible for the lawn erosion on the banks of Ferril Lake in City Park.

“The east shore of the lake between the lake and park road was fully dead, no grass, noxious spiky weeds had taken over,” Scarbeary said. “Overgrazing by geese and then the bulk of their poop had killed most of the grass.”

Canada geese are prodigious consumers of cultivated turf lawns. And where there is foraging, there is defecation. Lots of defecation. Geese poop every 20 seconds, dropping 1 1/2 to 3 pounds of feces a day, according to Colorado Fish and Wildlife, the Audubon Society and other stakeholders.

Just how many geese are creating large amounts of waste is also up for debate.

“As many as 20,000 Canada geese are residents of the Front Range and no longer migrate out of state,” wrote Cyndi Karvaski, the marketing and media relations representative for Denver Parks and Recreation, in an email.

But estimates from district supervisor Kendra Cross for the Animal and Plant Health Inspection Service division of the U.S. Department of Agriculture show about 44,000 mating pairs along the Front Range.

Canada geese require three conditions to establish residency — safety, food sources and mobility. City and Washington parks provide all three of these in abundance. Canada geese need open bodies of water to protect themselves from predators, as well as access to closely cropped turf grasses and open fields for predator sight lines and landing strips.

The geese population began its noticeable rise in the late 1990s, when climate changes including drought and rising temperatures left Denver’s turf lawns relatively clear of snow cover and park lakes free of ice, research shows. Before that, Denver was primarily a flyway stopover for migrating geese.

“In the past few years there has been an increased interest and effort in the Denver metro area to reduce and control goose numbers,” said Jim Gammonly, an avian research section leader for the Colorado Department of Natural Resources. “Hazing and egg-oiling efforts by property owners continues, but there is an increased desire to be more aggressive about lethal control.”

Oiling involves coating nest eggs with common household cooking oils to block air passages, preventing the embryo from developing. Hazing, using dogs or other noise makers, disturbs the geese’s sense of security in the hopes it will move on from a location. Such tools include the use of a remote-controlled robot referred to as a Goosinator, which simulates a predator.

But Vicki Vargas-Madrid, Denver Parks Wildlife administrator, said the method is not foolproof.

“A hazed flock might return to the same spot in as little as an hour, or by the next day,” she said.

More geese, more problems

Canada geese know no boundaries, leaving dense swaths of feces on lawns, sidewalks, roads, trails, plazas and playgrounds. The volume and mess from the defecation have discouraged some Denver citizens from using the parks.

“Without any publicity, we gathered nearly 1,500 signatures from an online petition urging the city to address our concerns about the overabundance of Canada geese in Washington Park,” said Steve Spirn, who works with a grassroots organization Citizens to Restore the Parks (CRP).

It’s more than just goose poop causing problems. Geese are traffic hazards when they cross streets, Spirn said. There are health concerns from pathogens and bacteria in their feces.

Gammonly noted that health concerns are not significant, but people with CRP disagree. CRP found research from institutions like Cornell University and Ohio State University that warn of waterfowl-borne bacteria leading to infectious diseases in humans. Researchers also found unusually high levels of such pathogens as coliform in Canada geese-infested reservoirs that supply drinking water.

One variable all parties agree on is the damage caused by goose excrement in water: The increase in nitrogen to the water of Denver Parks lakes and ponds encourages robust algae growth, robbing the water of the oxygen required to sustain a healthy fish and aquatic population.

Complicating the decision-making and administrative oversight of managing Canada geese is the labyrinth of federal, state and local agencies involved. Ultimately, the U.S. Department of the Interior regulates policies of the U.S. Fish and Wildlife division, which mandates regional, state and local policy. Through it, a division of the U.S. Department of Agriculture assesses flock damage. It, in turn, authorizes the Animal and Plant Health Inspection Service to oversee local management policies. If non-lethal logistics have been exhausted without results, the U.S. Fish and Wildlife will consider authorizing a depredation permit, which allows people to euthanize the birds.

Citizens to Restore the Parks offered assistance to the city, submitting strategy proposing the formation of a group of volunteers, but it has not been accepted. According to Spirin, city officials haven’t shown interest in pursuing his organization’s proposal.

The officials with Parks and Recreation say they are still finalizing their plan for dealing with geese this year.

“Our office of Natural Resources Wildlife Program has not yet finalized our goose management program for 2019,” Karvaski said. “There is no permit at this time that allows cities/counties/municipalities to lethally control Canada geese.”