The odd introduction

I recently addressed some of the many introduced species in Texas, including various deer in addition to blackbucks and aoudads.  It’s true that there are many nonnative mammals inhabiting the Lone Star State.

But what I want to address now is the odd introduction: the house finch (Carpodacus mexicanus).

A male house finch (Carpodacus mexicanus) perched on a reed (2009_11_26_042079)

This bird indeed is endemic to Texas.  In fact, Texas is the only place where the native territories of house finches and purple finches (Carpodacus purpureus) come close to each other.  Purple finches are an eastern species whilst house finches are a western species.

So to the chagrin of “purist” birders in North America, house finches are an introduced species everywhere east of the Rocky Mountains except Texas.  That’s right: if you don’t live in Texas and if you live east of the Rocky Mountains, house finches are a nonnative species.  To wit, you can lump house finches in with house sparrows (Passer domesticus) and European starlings (Sturnus vulgaris).

A male house finch (Carpodacus mexicanus) eating fruit (2009_12_20_045823)

Before the 1940s, house finches were resident only in Mexico and the southwestern United States.  But pretty birds don’t stay localized for long; people capture them and take them everywhere.  Then stupidity sets in and the birds wind up released.  So when “Hollywood Finches”, as they were called at the time, were deemed illegal east of the Rocky Mountains under the Migratory Bird Treaty Act, what did owners and dealers do with them?  They released them, of course.

A female house finch (Carpodacus mexicanus) perched on a branch (2009_11_07_037504)

According to scientific studies, house finches are shown to displace native purple finches in eastern North America.  In fact, they’ve also displaced house sparrows in some areas.  Sounds like pick your poison, or at least pick the lesser of two evils.

Most troubling, though, is the purple finch issue: purple finch numbers are declining throughout their territory, and evidence suggests that house finches and house sparrows are at least partly to blame (the two species have been documented as out-competing purple finches for food and nest locations).

A male house finch (Carpodacus mexicanus) perched in a tree (2010_04_03_052372)

So it goes without saying: if you live east of the Rocky Mountains but outside of Texas, and if you practice a “native first” mentality with regards to nature, house finches should be your enemy if you hate house sparrows and European starlings.  Otherwise you hate the native purple finch and you are hypocrite, cognitive dissonance notwithstanding.

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The next post in this nonnative series will be about a truly invasive species.  We’re terribly anthropocentric, so we call “introduced” species “invasive” since we don’t want to own responsibility for their presence.  But an invasive species is quite different from an introduced species: introduced means we’re responsible while invasive means the critters are responsible.  In the scheme of things, the vast majority of hated creatures are introduced, not invasive.  And some invasive species are loved, which is precisely the kind of species I’ll cover next.

And yes, I’m increasingly disgusted with nature purists.  How selective they are.  Shall I mention their dislike of brown-headed cowbirds and their attempts to kill this species in hopes of protecting other birds?  Shall I mention their disgust with house sparrows and European starlings whilst they pretend cattle egrets are A-OK?  Shall I mention their hate of rock pigeons while they ignore the hunting of mourning doves—deaths in the millions each year?  I’m only just getting started…

10 thoughts on “The odd introduction”

  1. Interestingly, here in Ontario our House Finches only range up to the edge of the Canadian Shield. On the Shield and in northern Ontario there just isn’t the sort of open habitat and human development that they need to grow a robust population. Here, Purple Finches occur throughout the province but are sparse south of the Shield, where the mixed forest habitat they prefer is limited. As some abandoned land succeeds into forest their numbers have been increasing south of the Shield, but strangely they have also been declining in their area of highest abundance, on the Shield. The decline can’t be attributed to House Finches, as the latter don’t much occur there. The cause is unclear and I don’t think much time has been spent looking into it for our populations, but a hypothesis is that it’s tied to the greater control and management of spruce budworm populations. Historically there used to be massive outbreaks of the caterpillars, but of course these were severely detrimental to the forestry industry. Since the start of budworm control programs and the subsequent reduction in the number and intensity of outbreaks, the populations of several budworm-specialist bird species, whether coincidentally or consequently, have declined. Purple Finches fall into this group, as do Evening Grosbeaks, a species that I remember seeing at our family’s feeders every winter growing up, but haven’t seen them at a feeder south of the Shield now in some fifteen years.

    I define “introduced” and “invasive” a little differently than you do, I think. I don’t find the two terms mutually exclusive. Introduced simply means to me that the species is non-native, and that it has been, whether intentionally or not, introduced by humans to an environment where it didn’t previously occur and would likely never have reached on its own. Invasive in my mind refers to the nature of what a species does when it finds itself in a new place – some may sit docilely where they were put and never spread very far (many garden plants and flowers fall into this category), but some others love their new location so well that they go crazy and start spreading out from where they were put. Some introduced species may not necessarily be invasive, while some invasive species could very well be native (especially true in disturbed areas, since it’s harder for anything – introduced or otherwise – to gain a foothold in an area of stable habitat; unfortunately, our human activities mean that few habitats are truly undisturbed anymore).

    1. You’re right, Seabrooke, that localized population changes can’t always be attributed to more prominent issues seen elsewhere. I do know here in eastern half of Texas that purple finches became extremely rare within a few years of the eastern population of house finches arriving. I used to see them every winter; now I can’t remember the last time I saw a purple finch here. But I’m certain there are a lot of different pieces to the puzzle and we’re just not seeing the big picture yet.

      You’re right: I tend to be strict on the use of invasive versus introduced, and I do it intentionally because so many people use the word “invasive” to cover everything. As nature pejoratives go, it seems easy to use that word and wash our hands of responsibility. That’s why I differentiate between the two even though there is logical overlap between them. It’s good to be reminded of that, so thank you!

  2. It was my understanding that House Finches were gradually migrating eastward from the West Coast and eventually would have become established east of the Rocky Mountains even without human intervention. Am I wrong?

    1. I hadn’t heard that before, Scott, so I did some checking. According to the distribution maps on Cornell’s BNA, from 1958-1990 the western population of house finches had a stable eastern territorial limit with only some eastward fluctuations in Texas. Also, I found a paper (Hamilton, T. R. 1992. “House Finch winter range expansion as documented by Christmas Bird Counts, 1950-1990”. Indiana Audubon Quarterly 70:147-153.) which shows the same stable territory for the western population. Based on those two sources, it seems like the western (native) population was only moving around in the west and somewhat toward the north, but they weren’t moving toward the east except in negligible increments in Texas.

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