Nearly extinct in the mid-20th century due to over-hunting, a whopping 280,000 Canada geese now live in Michigan, according to the Department of Natural Resources.
That means a lot of goose poop. One adult goose can produce up to 2 pounds of feces a day.
Too much waste can cause environmental problems, research shows.
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Goose poop contains high levels of phosphorus and nitrogen, which in large quantities cause eutrophication, or the growth of algal blooms on water bodies, according to a study from Kristianstad University in Sweden.
Excessive algal blooms are harmful to organisms living in or near the water. Algae overgrowth uses up all the dissolved oxygen in the water, essentially choking out and killing aquatic plants and animals, said Alan Steinman, a researcher at the Robert B. Annis Water Resources Institute at Grand Valley State University.
Decomposing algae sinks to the bottom of a water body, releasing nutrients and potent toxins into the water and surrounding ecosystem, which can kill other organisms that drink the water, Steinman said.
Phosphorus is typically a limited resource in an environment, which prevents excessive algae growth. But people have been inadvertently adding more phosphorus to waterways through fertilizer runoff, he said.
“We’re basically providing much more phosphorus, faster, than the algae needs,” Steinman said. “They’re saturated with phosphorus and they’re very happy to be as long as they have enough light, and warm temperatures for the blue-greens to grow.”
Nitrogen is another nutrient that algae thrive on. Unlike phosphorus, nitrogen pollution is harder to control because it originates from the atmosphere.
Steinman says more studies need to be done on the direct impact of goose waste on water quality.
“All of these estimates that go into the equation that determine the total load of phosphorus from goose poop – there’s going to be a lot of uncertainty,” he said.
The impact of goose droppings is more noticeable in areas with high concentrations of the birds. Otherwise, their influence is harder to measure, Steinman said.
He recommends people avoid water with visible algal blooms and keep pets from drinking it. While toxic algal blooms are rarely fatal for humans, pets are at higher risk of poisoning and death.
Swimming in contaminated water can cause skin irritation for humans but is not usually dangerous.
“I can’t explain why anyone would want to swim in an algal bloom – you could also get contact dermatitis and have some skin reactions, but it’s not fatal,” Steinman said.
Goose feces is also home to bacteria, parasites and diseases that can make you sick, according to a study by the U.S. Department of Agriculture’s National Wildlife Research Center.
Although human illness from goose poop can happen, it’s rare, says Barb Avers, a waterfowl and wetland specialist at the DNR.
“It’s very low risk unless for some reason you’re handling the poop,” she said.
Michigan’s increasingly mild winters are encouraging more geese to become year-round residents, eliminating the need for migration. And if they migrate, they don’t go far, Avers said.
Thirty to 40 years ago, the geese would migrate to southern Illinois and Tennessee, Avers said.
But now they travel only as far south as Ohio. The historic wintering grounds are seeing far fewer geese because of climate change, she said.
“They’ll go south basically as far as they need to,” Avers said. “What I have noticed is them doing a lot of bouncing back and forth.”
Geese need access to unfrozen bodies of water and exposed grasses for feeding. Milder winters mean ponds and rivers don’t stay frozen the whole season and there’s less snow cover, so they don’t need to leave to find food, she said.
The highest concentrations of geese are in the areas with the most people.