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Separating Finches
Species in the genus Carpodacus occur in environments as diverse as the mountains of Asia and the vast deserts of the Middle East. Here in North America, this cosmopolitan genus is represented by three similar-looking finches—the Cassin’s, Purple, and House finch—which are likewise distributed from the mountains to the deserts. All three species visit feeders frequently, occurring in different combinations in the East and West. House Finches were introduced to the eastern states around 1940, when caged birds were released in New York. Prior to this time, only the Purple Finch occurred in the East. In fact, the Purple Finch was once a common summer resident in southern New England, where it is now primarily a winter visitor. Since 1966, according to Breeding Bird Survey data, the breeding population of eastern Purple Finches has declined by 50 percent. This decline is often associated with the introduction of House Finches to the East, but urbanization and the disappearance of the American elm—a favorite food source of the Purple Finch—may be partly to blame. Eastern Purple Finches have erratic migrations in the fall. They move primarily from north to south throughout most of their range, but their movements are variable, probably best described as "biennial incursions." Every two years, Purple Finches appear as far south as northern Florida, Alabama, Mississippi, Louisiana, Arkansas, and Texas. Many researchers attribute these erratic movements to variability in the birds’ food sources. The House Finch shows different migratory patterns in different parts of its range: the native western population is nonmigratory, whereas the introduced eastern population is partly migratory. The eastern House Finch continues to expand westward into the Great Plains, where it may have met the western population in recent years (see map ). Data from the Lab’s House Finch Disease survey suggest that the migratory habits of eastern House Finches may be an important factor in causing conjunctivitis to spread so widely and rapidly through their population. Cassin’s Finch, Purple Finch, and House Finch are all native to the West. Though these three species have similar plumages and basic ecology, they have different preferences in terms of elevation, habitat, and foods. These differences result in a complex distribution of the three species in the West (see map ). The western House Finch is primarily a species of low, dry habitats and is found in deserts, canyons, ranches, and towns. The Purple Finch prefers moist, shaded forests at low and middle elevations and is confined primarily to the Pacific states and provinces, from British Columbia to Southern California. The Cassin’s Finch prefers cool, semiarid coniferous forests and is usually found at higher elevations than the Purple Finch in the Sierra Nevada Mountains. It is the only Carpodacus finch found at higher elevations in the Rocky Mountains. FeederWatchers must pay close attention when trying to identify these three species, especially in areas where all three of them occur (for example, the Sierra Nevada Mountains) and in the Rocky Mountains and Southwest states, where the Purple Finch is rare. The accompanying "FeederWatch-ers’ Notebook" has tips on distinguishing between the females of these three species, which—especially the Purple and Cassin’s finches—can be particularly difficult to separate. As for adult males, Purple Finches tend to be rose red over most of their body, especially bright on their head and rump; Cassin’s Finches are very similar but the red of their throat and breast is paler, and their crimson cap contrasts sharply with their brown nape; House Finches usually have a bright red bib, forehead, eye stripe, and rump, and a brown cap. Although all three species eat a mainly vegetarian diet, they show marked preferences for particular foods. Purple Finches primarily eat the seeds and buds of several species of trees, including fruit trees. Cassin’s Finches also eat seeds and buds, but not much information exists on their feeding preferences. Anecdotal evidence suggests that in winter, the buds of conifers form the bulk of their diet, and in summer they are fond of the buds of quaking aspen. Western House Finches do not appear to be tree-seed specialists: in the winter they prefer weed seeds such as thistle, mustard, alfilaria, knotweed, and mullen. They can be an orchard pest in summer, feeding on commercial fruit. The House Finch is one of the few species of birds that feeds its young exclusively on vegetable matter. In the West, the migratory habits of these three species also differ. The western House Finch is nonmigratory. The Purple Finch shows north-to-south migratory behavior, but does not stage irruptions as it does in the East. The Cassin’s Finch, on the other hand, occasionally migrates altitudinally, traveling to lower elevations during winter. In The Birds of North America, Hahn writes that "their occurrence at any given locality is highly variable from year to year. Despite the prevalence of this finch, remarkably little detailed work has been done on it, leaving many possibilities for new discoveries." Your participation in Project FeederWatch can open the doors to these new discoveries. Thanks to your help we have already documented the expansion and population changes of eastern House Finches and the rise and spread of House Finch conjunctivitis. With careful observation and the ability to distinguish between these three similar species, you can provide us with data that will enable us to study patterns in the seasonal movements of Purple Finches and Cassin’s Finches, and clarify the relationships between these two species.
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