Here is an assertion that might startle you:
“One of the most notable ornithological events of the 20th century has been the spread of the house finch. …”
That’s from the American Ornithological Union’s monograph on the house finch published in 1993.
And yes, it’s true. And not only that: Grand Forks and the Red River Valley have been on the front line.
Probably no species has made a bigger difference in the bird population here than the house finch, and in so short a time.
Yet this was among the last areas conquered by the house finch. House finches showed up here 30 years ago or so.
In three decades, they’ve pretty well displaced an earlier immigrant, the house sparrow. House sparrows still occur here, but they are fewer by far than they once were, in Grand Forks, at least.
House finches are more.
Not only that:
The house sparrow has become a bird of small towns and farmyards.
The house finch is a city bird.
This is remarkable because it is the reverse of the usual. House sparrows long were regarded as avian pests of urban areas, while house finches were seen as birds of the Western countryside.
These two species are not very closely related, though they share some preferences. This is clear from their names. They like human company.
What’s not so clear is that both of them are opportunists.
The house sparrow—neither a sparrow nor a finch exactly, but a weaver finch, a singular subset of birds—is an immigrant from the Old World, brought to North America by a homesick Englishman who wanted to establish in America every bird species mentioned in Shakespeare’s works.
The house sparrow is an alien, in other words.
Nevertheless, the house sparrow quickly conquered North America. From its introduction in New York in the 1880s to its arrival in Alaska required only five decades.
The house finch story is similar—and yet opposite. The house finch is a native American bird. Its prehistoric range apparently extended from southwest Nebraska southward to Nicaragua and westward to the Pacific Ocean.
And then, in 1940—not so long ago—a dealer in caged birds released some of his stock on Long Island, N.Y.
The rest is history.
The house finch spread across eastern North America with astonishing speed. In less than 50 years, it had reached Grand Forks, more than 1,500 miles from the point where it was released.
At the same time, house finches began moving eastward from their native range.
Almost certainly, house finches reached Grand Forks from the east and not from the west, where it was a native species—even though native house finches flourished much closer to Grand Forks.
How could this be?
Only because the Western birds were quite settled, able to produce new generations, not stressed to find new territories.
In other words, well-established in the evolutionary scheme of things.
But the birds introduced in New York?
They needed to adapt, and quickly, to new conditions.
That’s what they did.
As they did, they “increased and multiplied,” as the Bible suggests they should have.
But this collided directly with that other immigrant species, the house sparrow.
House sparrows and house finches have similar habitat preferences. These aren’t tied to humans, even if their names imply it. In the absence of humans, both species will find appropriate nesting sites.
House finches raised the stakes, though.
Unlike the house sparrow, which wants a cavity, the house finch is happy to place its nest in an evergreen shrub planted close to a building, for example, or above a light fixture on a door front.
But that’s not all.
The house finch is a belligerent bird. It doesn’t hesitate to trespass on territories the house sparrow holds, and so it is able to drive the house sparrow away, house by house, block by block, neighborhood by neighborhood.
Not only that, but the house finch announces itself—and advertises its territory—in ways the house sparrow just can’t answer.
Advantage? House finch.
Of course, neither belligerent had knowledge of what was taking place; each acted in its own best interests.
The result is a change in the bird life of North America, in favor of a native species, the house finch.
This is clear in Grand Forks, where house sparrows have declined year over year, and house finches have increased, as recorded by the annual Christmas bird counts.
Should we prefer one species or the other?
That’s really not for us to decide.
House sparrows and house finches will respond to conditions as they occur, and their responses will have impact on future generations—that, after all, is what evolution is all about.