The wild bird population in the continental U.S. and Canada declined by almost 30% from 1970 to 2018, according to research published in the September 2019 issue of “Science.”

The research cited habitat loss as the top contributor to the population plunge. But much of the decline can be attributed to the law of unintended consequences.

Unintended consequences are the unplanned outcomes of purposeful actions. The consequences can be beneficial, harmful or neutral; in the case of birds, they are nearly always harmful.

This column is about actions by people who like birds but who unwittingly harm them. For advice, I turned to the Cornell Lab of Ornithology and to Cindy Daily and Joseph Molotsky of Discovery Bay Wild Bird Rescue (Discovery Bay WBR) in Port Townsend.

Question: Have you ever tossed an apple core out the window of a moving vehicle? I have. It’s not littering, I told myself, because an apple core will biodegrade. Plus, maybe it will be a meal for an animal.

I meant well but I overlooked a potential unintended consequence: Too often a discarded apple core attracts a rodent, the rodent attracts an owl, hawk or eagle, the raptor prepares to grab the rodent and—bam—the bird is blindsided by a motor vehicle.

If the bird is lucky, it survives the collision without aid or it receives aid at Discovery Bay WBR or another wild bird rehabilitation center. There, it might recover and one day be released, or with care it might survive but be too damaged to return to the wild.

Discovery Bay WBR cares for 400-500 birds a year. Many are collision survivors whose injuries will deprive them of freedom for the rest of their lives—the victims of people who didn’t mean to maim a bird but who inadvertently did by tossing food waste from cars.

The list of unintended consequences involving birds is long and, surprisingly, my columns are length-restricted. So, without further ado, more behavior that indirectly harms birds, as well as ways that harm can be prevented.

Glue Traps: They catch mice and rats, which attract owls. The owls’ feet, wings and beautiful faces bond to the glue. Eventually the birds succumb to horrible deaths. If they have chicks, the chicks starve. Solution: Don’t use glue traps.

Snap Traps: Think spring-loaded mice and rat traps. They aren’t intended for birds, and yet a robin was recently brought to Discovery Bay WBR with its legs cut in half by one of them. Snap traps kill countless birds. Solution: Don’t use them.

Windows: What’s the harm in windows? To us, nothing, but birds cannot see glass. It’s why they so often fly full speed into windows. Two solutions: UV reflective anti-collision window bird decals (on Amazon) and Acopian BirdSavers (at BirdSavers.com). 

Bird Feeders: Watching birds eat is fun. But if there are cats about, they will catch songbirds. Solution: Keep the cats inside or gift the feeder. Also, feeders can spread diseases among birds. Solution: Clean your feeder weekly with watered-down bleach.  

Lead Poisoning: You enjoy hunting and/or fishing. Fine. But wetland birds eat lead shot. Seabirds eat lead fishing weights. Raptors eat lead from gut piles and unrecovered deer. Lead kills birds. Solutions: Non-lead sinkers and non-lead buckshot and bullets.

Fishing Tackle: What’s the harm in leaving a little fishing line and some messy hooks behind? The line often ends up wrapped around birds and birds often mistake shiny hooks for food. Solution: Fishermen, please don’t leave tackle behind.

House Cats: In the U.S. alone, house cats kill more birds than collisions with windows and cars combined. Solutions: Keep them indoors, outfit them with Beau’s Bells for cats or bird-safe collars, or build or buy a catio (on Amazon).

Bird Netting: Also called garden netting, it’s generally a soft filament used to protect plants from birds. All too often birds get tangled in it and die from loss of blood flow, dehydration or strangulation. Solution: Buy stiff bird/garden netting, not the fine stuff.

Rat Poison: The unintended consequence of putting out rat poison is that the poisoned rodent is often caught and eaten by an eagle, owl or other raptor, which ingests the poison along with its prey and dies. Solution: Mouse Motel (on Amazon).

Angel Wing: What’s wrong with feeding bread to ducks and geese? It can cause angel wing, a syndrome that results in deformed wing bones. The abnormality renders the bird flightless for life. Kindness can kill. This is a case in point. You know the solution.

Cindy Daily, the director and chief rehabilitator at Discovery Bay WBR, a nonprofit I’ve given generously to and encourage you to do the same, asked that I ask you to stop intervening in nature.

“For example, a hawk has just caught a pigeon and people rush over to chase away the hawk to save the pigeon,” she said. “Now, we might not like to see the hawk kill the pigeon, but it is the way it’s supposed to go.”

Daily has been rehabilitating birds for 40 years. She’s grown weary of people who show up with mauled pigeons “saved” by well-intentioned people. The pigeon often dies and “the hawk missed a rightfully caught meal. Nobody wins.”

Scott Doggett is a former staff writer for the Outdoors section of the Los Angeles Times. He and his wife, Susan, live in Port Townsend.