When wildlife illustrator Emily Poole found a dead pine siskin behind her local bookstore in Eugene, Oregon, in January, she called her partner, who works at a bird-feeding supply store. He told her that numerous pine siskins — a type of migratory finch — have been dying of salmonellosis this winter.
Caused by the salmonella bacteria, the disease has proliferated across the Northwest from British Columbia down to Northern California. The likely culprit? Bird feeders.
February is National Bird-Feeding Month, usually a time for celebrating feathered creatures and providing extra food and water to get them through the winter. But if you’re hanging a feeder, then forgetting about it for weeks, you may unknowingly be putting your local birds at risk of illness or even death. Ornithologists and other bird experts across the country agree that cleaning your feeder several times a week and maintaining the ground below can help your avian neighbors stay healthy.
Bobby Fokidis, an associate professor of biology at Rollins College in Orlando, Florida, focuses on how urban environments affect bird health, as well as the link between stress and disease in songbirds. He says many avian diseases — including conjunctivitis, avian pox, trichomoniasis and salmonellosis — have historically been linked to congregations at bird feeders.
Salmonellosis most often affects goldfinches, evening grosbeaks and house finches. Pine siskins are particularly susceptible because of their tendency to flock together in groups. If an infected bird defecates on the ground under a feeder with spilled seed and another bird flies down, picks up a seed and ingests the feces, that other bird can also become infected. Birds with salmonellosis become dehydrated and emaciated, eventually dying of starvation. There’s also a risk of the disease being transferred from one bird species to another due to the intermingling that occurs at feeders — something that’s rare in nature.
“Birds will often visit multiple feeders in an area, especially migrating flocks and wintering birds — such as the pine siskins that are affected here in Florida — and these can serve as the equivalent of ‘superspreader’ events for diseases like salmonella and avian pox,” Fokidis wrote in an email. “Migrating birds can be particularly susceptible because they are already energetically compromised, risking a less effective immune response.”
Fokidis said people in areas with known cases of salmonellosis should take down their feeders, especially if they have seen sick or dead birds, until the outbreak has cleared up.
“Many studies have shown declines in songbird numbers, and bird feeders are often encouraged as an active way that citizens can both engage with birds and assist them as they endure cold winters and long migrations,” he wrote. “But when disease is around, we have to make the adjustments needed to control that disease.”
Dan Gleason, a retired ornithology teacher, co-owns Wild Birds Unlimited in Eugene with his wife, Barbara. They have fielded numerous calls about sick and dying birds in the past few months.
The Gleasons tell people who have observed lethargic or dead birds around their homes to take down their feeders for two weeks, so local birds can disperse and find food in the wild. After that, they say, it’s safe to rehang feeders — if you’re diligent about cleaning them. They suggest soaking all types of feeders every other day in a sink filled with 10 cups of hot water to one cup of bleach. Rinse the feeders with hot water, and dry them thoroughly before putting them back out. “Hang only the number of feeders that you can maintain comfortably,” Dan Gleason said.
He also urges people to clean their birdbaths every other day with a hose or a stiff-bristle brush. “If you’re just going to leave your feeders and baths up and ignore them, then keep them down,” he said.
The Gleasons note that people can contract the salmonella bacteria if they’ve been in contact with birds or their feces, or with cats that catch infected birds. Wear rubber gloves when cleaning feeders and birdbaths, they said, and scrub your hands afterward to avoid contamination.
Wesley Hochachka, a senior research associate at the Cornell Lab of Ornithology, said in an email that tray feeders — platforms where multiple birds can stand and eat — are more likely to accumulate feces and seed on the ground, which can spread disease. He instead suggests a tube feeder, with holes up and down the sides. But even then, he says, clean frequently to remove bacteria. “Tube feeders are not perfect, because birds’ heads will come into contact with the sides of the tube when the birds are reaching for food, so keep surfaces as clean as possible,” he wrote.
He notes that the salmonella bacteria can survive for long periods of time, accumulating on or under a bird feeder. To guard against contamination, he tells people not to leave piles of seed on the ground and says to move feeders if birds regularly feed underneath them; place pieces of cardboard under a feeder and replace them regularly if you notice a large number of redpolls or pine siskins in your yard, he says.
Hummingbird feeders present their own challenges. Long, bottle-style feeders with yellow plastic flowers around the nectar holes are breeding grounds for mold. A shallow dish feeder is a safer choice. Regardless of which you choose, clean your feeders once a week during cool weather, and twice a week when it’s warm. Soak all feeder parts in a sink with one cup of vinegar to two cups of hot water, then scrub them with a thin-bristle brush or pipe cleaner and dry them thoroughly before filling and rehanging the feeder.
Homemade nectar should be one part sugar to four parts water, boiled for two minutes. The Gleasons caution against using raw sugar, which is colored by molasses, which hummingbirds can’t digest. They say never to use honey, which contains spores that can cause fungus to grow on a hummingbird’s tongue. Change nectar weekly in the winter and more often in the summer, when warmer temperatures can increase mold growth. And avoid adding red dye or purchasing a packaged red nectar powder, which can put hummingbirds at risk of health issues, Dan Gleason said.
Poole, the wildlife illustrator, has taken down her seed feeders for now. She’ll put them back up when the region’s salmonellosis outbreak has passed, she said. But even if you don’t live in an area affected by the disease, it’s critical to keep your feeders clean to avoid spreading harmful bacteria.
For many, providing seed and observing wild birds represents a rare pleasure during the pandemic. A salmonellosis outbreak isn’t a dealbreaker for backyard birders, but it is a call to ensure we take whatever steps we can to keep our feathered friends safe.