The two most common finches showing up in wildlife rehab in Colorado are House Finch and American Goldfinch; their natural histories here were designed to inform rehab volunteers.
House Finch—the ubiquitous fruit biter
House Finches are a very common sight in Colorado. They can be found in every county and they breed in all but 3 high mountain counties here. Originally, House Finches resided only in Mexico and southwestern US. But they were illegally sold as caged birds in the east in the early 1900s. With increasing enforcement in the 1940s under the Migratory Bird Treaty Act, which made it illegal to capture or sell most wild birds, some pet shop owners on Long Island, NY, allegedly just released their inventory of House Finches. The House Finches found that they rather enjoyed the Atlantic seaboard—and the rest, as they spread inland, is avian invasion history.
Most of the time, House Finch males have red foreheads and red stripes over the eyes, as well as red on the breast and the rump; the rest is rather drab, streaky brown. A female or a young bird is basically brown with a heavily streaked breast and belly. However, you might see a male that is yellow- or orange-colored. This color variation primarily reflects a diet that is low in carotenoid pigments—yellow, orange, or red fruits and vegetables. Females seem to prefer the reddest male available, perhaps reflecting the odds that that guy will be able to provide lots of appropriate food for her and the kids
A House Finch’s diet is 97% vegetable matter—buds, grain, seeds, and fruit. Their main source of animal matter is probably whatever bugs they eat while they’re gobbling up plant parts. Parents initially feed their young through regurgitation of their crops. Nestlings fledge 12 -19 days after hatching and follow their parents, begging noisily, for another 2 weeks. Early in the breeding season, the male will continue to feed the fledglings while the female starts a 2nd brood; late in the season, both parents feed the noisy little beggars. Here’s a photo of a dad feeding his kids. (By the way—those downy tufts of feathers, especially on the tops of their heads, are a good way to identify even the youngest House Finch chick.)
The scientific name of the House Finch is Carpodacus mexicanus. “Carpodacus” means fruit biter, from the Greek words “karpos” (fruit) and “dakos” (biter). (Mexicanus reflects the bird’s original range.) So, if you’re on a shift and you have young House Finches that are beginning to self-feed—make sure that, in addition to seeds and water, there is plenty of fresh fruit cut into very small pieces for the growing “fruit biters.”
American Goldfinches—a harbinger of summer’s close
Many people think of robins as harbingers of spring. I think of American Goldfinches as harbingers of the end of the avian breeding season. Sometimes referred to as the “wild canary,” the American Goldfinch is one of the latest breeders in North America. The scientific name is Carduelis tristis—from carduus (Latin for “thistle”) and tristis (Latin for “sorrowful”). Since thistle is one of the most important foods for the American Goldfinch, the root of the genus name is obvious. The species namet(ristis) probably comes from its song, which is a bouncy jumble of notes with a descending note thrown in occasionally that (to some, at least) might sound a bit sad. You can hear snippets of this song (and lots of examples of their call notes, which some humans refer to as their “po-ta-to chip” call—click on “songs and calls of American Goldfinch”). The male in breeding plumage (here, enjoying some eponymous “carduus”) is unmistakable: bright yellow body with a black cap (pulled low over his forehead), black tail, and black wings with bold white wing bars. The male in non-breeding plumage and the female all year long are much less spectacular—a drab olive-green or brown and no black cap.
These goldfinches can often be identified from far away, especially in flight. They have a very distinctive, deeply undulating (up and down) flight because they do several flaps that send them up and then a close-winged glide that sends them down. They often give their characteristic “potato chip” call as they begin the downward glide.
American Goldfinches start breeding in early July, just as most other songbirds are wrapping up the season. They postpone breeding until grass and weed seeds (especially thistle seeds) are plentiful, which doesn’t occur until mid- to late summer. Their nests are strips of bark held together by spider webs and caterpillar silk; they line the inside with plant down from milkweed, cattails, and (of course!) thistle. The nests are often so tightly woven that they can actually hold water, which can pose a serious hazard for very small nestlings during a heavy rainstorm, unless a parent shields the nest. Unlike most songbirds, who feed their kids lots and lots of insects, goldfinch parents regurgitate a slurry of primarily seeds for nestlings. A staple of the parents’ diets (and therefore the babies’ diets), thistle seed is extremely high in protein—much higher than other seeds. So even though insects probably are not a big part of their diet in the wild, we feed goldfinch babies the same high-protein diet as all of the other nestlings so that they get that extra protein that they need. Parents feed their kids at a relatively slow rate, compared to the frenetic pace of other songbirds—about once every ½ hour or hour. Nestlings fledge between 11 and 17 days after hatching, remaining with their parents for about 3 weeks after that. Alas, once you start to see goldfinches raising babies, you know that the summer season is on its downhill slide into the fall—and the fall baby squirrel season is on its way.
© 2009 Tina Mitchell
