I’ve just returned from a meeting in Miami. Alas, I had no free time to go birding, but I certainly saw many rock pigeons and house sparrows. One expects to see these two species in any urban environment.

The two are both introduced species. In North America, they are rarely found very far from human-altered landscapes. I see a fundamental difference in the habitats of these two species.

A few decades ago, my wife and I toured Scotland. At the northeast tip of land, wild rock doves were nesting on dramatic cliffs and permitted no close approach by humans.

Humans obviously befriended some rock doves, which readily adapted to urban and agricultural habitats. Don’t expect to see rock doves in Baxter State Park or other areas with sparse human density.

Finding house sparrows in a city is a snap. But where you would you go to find them in the wild? A small population of house sparrows in the Middle East associated with natural grasslands are the only “wild” house sparrows extant. This population is genetically distinct from all other house sparrows.

The vast majority of house sparrows are associated with humans. Their “natural” habitat is best described as human-altered landscapes.

With the exception of Middle East grassland house sparrows, these birds have married their fortunes together with humans. The presence of humans has certainly facilitated the natural spread of the species into Europe and Asia.

The original range includes northern Africa and most of Eurasia. The species has been introduced to North and South America, Australia and New Zealand. Pinning their success to humans, house sparrows are doing well and certainly outnumber humans on this planet.

House sparrows were introduced in North America as releases of birds in Brooklyn in the fall of 1851 and spring of 1852. The invasion of North America was aided by subsequent introductions in San Francisco in 1871 and 1872 and in Salt Lake City in 1873 and 1874. Now, house sparrows are found throughout the lower 48 states, except for southwest Texas, and over much of Canada. They have not become established in Alaska yet, likely because the relatively sparse human population in that state limits their habitat.

An introduced species may wreak havoc on native species. House sparrows readily nest in cavities, and bluebirds, tree swallows and house wrens may lose nest cavities to house sparrows.

From personal experience, I know that house sparrows will enter nest boxes occupied by bluebirds, then kill the nestlings and take over the nest box. An effective deterrent is to have nest box openings no greater than 1.25 inches in diameter. That opening gives access to bluebirds, swallows and wrens but not the chubbier sparrows.

In 1958 in China, Mao Zedong declared house sparrows to be one of four pests that needed to be eradicated, and people were told to kill as many as possible. Perhaps over a billion birds were eventually exterminated.

Rice crops seemed to improve at first, but the insects feeding on the crops increased rapidly as the population of house sparrows decreased. As a result, more rice was lost to the insects than to the birds.

Mao later reversed his position, ordering the protection of the house sparrow. Not long after, rice production improved – thanks to the dietary needs of nestling house sparrows.

Herb Wilson teaches ornithology and other biology courses at Colby College. He welcomes reader comments and questions at

whwilson@colby.edu