Non-natives carry big consequences

Non-natives carry big consequences

My house cats think I am a genius. Through their eyes I have used my upright posture and opposable thumbs to create an attraction just outside the kitchen window that draws birds like moths to a flame. All day long from dawn to dusk, the little, brown creatures come and go in rapid succession.

Five, 10, sometimes 50 at a time they swarm onto my swinging, seed-filled feeding station, entirely unaware of the dangerous predators crouching in plain view just beyond the glass.

My bird feeders offer hours of entertainment for my house-bound felines, and the cats get out of it exactly what they deserve — an opportunity to practice their stalking skills and exercise their predatory instincts with absolutely zero chance of capturing and killing a bird.

House cats are a non-native species here in North America, and allowing them to roam at large in the great outdoors would be both irresponsible as a pet owner and contrary to a lot of the things I stand for as a conservationist. Studies have indicated feral and free-ranging cats (pets allowed to run at large) capture and kill an estimated 1.3 to 4 billion birds a year in the United States.

Song birds in North America have been in steep decline for decades, and while cats are undoubtedly a huge contributor to this alarming trend, there are other factors at work as well. Habitat loss in the form of urbanization, deforestation, sprawling development and even changing cropping practices all figure heavily into the equation. Artificial lighting, especially in downtown areas during peak migration periods, can lead to devastating losses as well.

One factor in North America’s songbird decline that many folks might not think of, however, is the displacement of our native songbirds by invasive, non-native bird species.

If one would like to see the perfect example of this phenomenon, they would need to travel no further than my own small-town backyard. I’d bet there are hundreds if not thousands of individual trips to my feeders in the course of a day. At any given time, there are 20-50 birds waiting their turn on the low branches nearby. If you visit, however, you can confidently leave your field guide at home as nearly 100% of my feathered guests are one of just two species: English sparrows or European starlings.

History offers a solid account of how the problem arrived at my doorstep. English sparrows were released in the New York borough of Brooklyn in the year 1851 in hopes of controlling a caterpillar problem. From there they quickly spread throughout the majority of the continent to become one of our most numerous birds, presently estimated at about 200 million individuals.

The Cornell Lab’s extraordinary All About Birds website tells us European starlings arrived under even more dubious circumstances in the 1890s when a group of well-meaning literary types sought to welcome to North America every bird mentioned in the works of William Shakespeare. The starling now ranks as the sixth-most common bird on the continent.

The lesson we’ve learned the hard way, of course, is you can’t bring a new species into any ecosystem without affecting another that was already there. Invasive species compete for and exploit the same resources as native species but are oftentimes able to do so largely unchecked because the predators that controlled them in their own native environment are absent here. The playing field is unfairly tilted in favor of the newcomer, and the old-timer suffers. It’s a huge issue with enormous consequences, and it plays out in ecosystems all over the world. Join me next time to dig in deeper to the issue.

If you have comments on this column or questions about the natural world, write The Rail Trail Naturalist, P.O. Box 170, Fredericksburg, OH 44627, or email You also can follow along on Instagram @railtrailnaturalist.

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