Friday, July 18, 2008

Little Yellow Fellows

American Goldfinch
Photo by David Powell

In the world of birds there are no books; the language is unfamiliar to two-legged mammals, and self powered flight is almost a given. Of course, exceptions occur to most of the above phrases; birds don’t print or read books; some birds do mimic human speech and some humans can correctly interpret the meaning of bird sounds; and flightless birds, such as the Kiwi, the Weka, and the Emu, traverse the same paths as land-bound mammals. As with many apparent rules that govern our planet, the only hard and fast reality may be to expect the unexpected, and that the chaos theory is alive and well.

The question arrived via e-mail just the other day. In late June or early July, a Jemez resident had noted a bright yellow bird with a black cap, and wondered if it might have been a Wilson’s Warbler, a small songbird that primarily eats insects. Now, the books that determine where birds nest, winter, and migrate state that while Wilson’s Warbler travels through New Mexico during migration, sometimes in staggeringly large numbers in the fall, the breeding range occurs father north. Additionally, there are almost no recorded sightings of this species during the breeding season (June), another indication that the species nests elsewhere. However, New Mexico is a large state, and the Jemez region is definitely under-birded by the ornithological community. And, birds don’t read the books!

Among scientists, there is a theory that all bird life evolved in the tropics, lush habitat with few temperature extremes. In this Garden of Eden, food was plentiful and animal forms flourished, increasing their populations and evolving into additional species. Population expansion, in turn, may have taxed food resources, forcing animals to expand into nearby areas in search of sustenance and breeding territories with less competition. Birds, with the power of flight, could travel the greatest distance, easily reaching temperate zones. Here, these pioneer birds found abundant food, nesting habitat, reduced threat of predation and competition for resources. The limiting factor for temperate zone nesters was, and remains, weather extremes and the associated food shortages.

Perhaps the little yellow bird with the black cap was a pioneer, exploring new habitat, and searching for better nesting territory. Another well-documented pioneer set up shop along the Rio Grande in the summer of 2007, singing his heart out for a full six weeks. As of this writing, it remains unknown if the Chestnut-sided Warbler attracted a mate. If he did, and they were successful, then there is a good chance that they would return to the same area the following year, thereby expanding the range for their species. Range expansions for some species are well-documented, such as the White-winged Dove, and the Great-tailed Grackle. And just last year, in July 2006, Jo Wargo, US Forest Service Biologist, and I found a singing American Goldfinch along the Jemez River. With a bright yellow body and perky black cap, it might have been mistaken for a Wilson’s. Also out of range, this bird should have been to the north, in Colorado or beyond during nesting season. That goldfinch was well documented, and has been added to the reports for this species in New Mexico, although a nest was not found. In 2008, another American Goldfinch was observed in the same general area, perhaps representing a range expansion.

Our little yellow goldfinch of summer and cousin to the American Goldfinch, is the less common, and more range restricted Lesser Goldfinch. Like the birds above, its body is bright yellow, but the black on its head trails down the back of the neck (nape) and covers its back. His sweet song brightens summer days when most of the other songsters have finished their last aria. Like its cousin, it is one of the last to begin nesting, often not until the summer monsoon season, when its preferred foods, thistle, sunflower, and other weedy plants, set the seed crop that will easily satisfy the rapidly growing young as well as their parents. Uniquely adapted for seed-eating, their diet is almost entirely vegetarian, unlike most other birds. In fact, it is the goldfinch’s mostly vegetarian diet that makes them a poor host for the nest parasite, Brown-headed Cowbird. Although cowbirds do select goldfinch nests in which to deposit their eggs, the young cowbirds are unable to thrive on the seed only diet lacking in animal protein, and do not survive.

Both goldfinches adapt well to human activities and can be found in weedy fields, as well as in your own back yard. To attract goldfinches to your back yard, consider hanging a thistle, or niger, feeder. In New Mexico, you might just see the bright yellow Lesser Goldfinch during the summer, replaced by its northern cousin the American Goldfinch during the winter. At the higher elevations in mostly coniferous forest, thistle feeders will attract another finch with only a hint of yellow in its wings and tail, the Pine Siskin.

These hardy little birds are survivors in a human dominated world, and in fact, populations have benefited from our activities. The only threat reported in the literature is capture for the pet trade! While this is unthinkable within our country’s borders, our little yellow fellows spend at least a portion of the year in the tropics where there is little protection or understanding of the impact of poaching on wild populations.

The identity of the little yellow bird that was the subject of the question that motivated this article–what it mighta’ been, coulda’ been, but shoulda’ been–is anyone’s guess.

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