Last week, I wrote about keeping our backyard birdhouses free from debris, parasites and dirty materials. This week, I’d like to discuss how to keep them free from another problem: invasive bird species.

It’s difficult to think of cute, little birds as a danger, but many do pose a definite threat to some of our Texas native bird species. The house sparrow is among the worst since it is the most widespread and a truly invasive species here, threatening the native species’ balance in this ecosystem.

Let me explain.

Sparrows interrupt the progress of native birds in many ways. Due to their high population, typical of any invasive, they compete and win out at finding proper nesting sites. They’ve even been known to kill native birds, their young and their eggs. Invasive overpopulation takes up most of the food at the feeders and drives away less aggressive native species, such as bluebirds, martens and swallows.

I understand that many people just love to watch birds, of any kind, and having lots of sparrows doesn’t matter. But to many others, sparrows mean less of the beautiful songs and colors of other native birds.

One way to discourage invasive species from building in your birdhouses is to make sure the hole is the proper size. Depending on which type of bird you wish to attract, the hole size is very specific.

An Internet search or a birding book can help you to find the proper dimension you need. If you have a pre-built birdhouse and the hole is too small, file or cut it larger. If the hole is too large, simply place a thin piece of wood with the proper hole size over the existing hole.

Another way to discourage invasives is to make sure you don’t have a perch outside the hole, which helps invasives enter more easily. If you see an invasive bird building a nest, consistently cleaning it out may discourage it from returning, leaving the birdhouse available to a native bird.

Starlings, grackles, rock pigeons and cowbirds are other invasive species that threaten Texas native birds. Due to the viciousness and aggression of many invasive birds, there are government agencies and wildlife conservationists developing and carrying out programs to lessen the effects of invasive species in our area.

Darla Menking is a certified Bell County Texas Master Gardener and a Texas Master Naturalist. Email her at

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