Everything you ever needed to know about House Finches, but were afraid to ask....Alex Lees
Systematics
Geographic Variation
Substantial variation in body size, bill size and shape, wing and tail length, tarsus length, and plumage coloration among subspecies and populations in different regions (Moore 1939, Aldrich and Weske 1978, Power 1979, 1980, Hill in press a; Appendix). Birds from Guadalupe Is. are much larger than those from other populations (Power 1979, 1980). Aldrich (1982) reported that introduced eastern birds had larger bills and smaller tarsi than birds from parent population in California, but Hill (in press a) found no size differences among these populations (Appendix). Variation in male plumage coloration among populations is so striking it prompted Grinnell (1912) to give House Finches introduced to Hawaii species status (C. mutans) because of yellow and orange coloration of males. Feeding experiments with captive males, however, show dietary access to carotenoid pigments during molt determines male coloration and is responsible for inter- and intra-population variation in male coloration (Brush and Power 1976, Hill 1992, in press a; see Appearance). In contrast, captive feeding experiments indicate that variation among populations in the extent of ventral carotenoid pigmentation and discreteness of color patches on the head and breast (Moore 1939, Hill in press a) reflects genetic differentiation among these populations (Hill in press a). A single hybrid male from a C. m. griscomi x C. m. frontalis cross expressed a patch size intermediate to the two parental types (Hill in press a). See Hill (1992, in press a) for detailed discussion of determinants of inter- and intrapopulation variation in coloration and color pattern.
Subspecies; Related Species Moore (1939) divided House Finches into 4 species with a total of 18 subspecies. Subsequent treatments of the U.S. and Baja California populations (American Ornithologists’ Union 1957, 1983; Grinnell and Miller 1944) largely followed Moore’s taxonomy except that (1) the Hawaiian population is ascribed to the subspecies of the California population (C. m. frontalis) from which it was derived, (2) the 2 island species recognized by Moore (C. amplus and C. mcgregori) are considered subspecies of C. mexicanus (C. m. amplus and C. m. mcgregori), and (3) 4 western U.S. populations (C. m. frontalis, C. m. grinnelli, C. m. smithi, C. m. solitudinis) recognized as distinct by Moore are subsumed under C. m. frontalis . Many of the populations in Mexico and among the islands of the Pacific coast are geographically isolated and morphologically distinct (Moore 1939, Power 1979, 1980, Hill in press a), but a thorough study of the systematics of the group is needed.
Proximate Control Of Coloration
Yellow/orange/red color of feathers results from deposition of 3 carotenoid pigments: ß-carotene, which produces yellow to orange color in feathers; isocryptoxanthin, which produces orange color in feathers; and echinenone, which produces red color in feathers (Brush and Power 1976). Controlled feeding experiments with captive House Finches indicate that all individuals in all populations have same potential to be brightly or drably plumaged; variation in color of feathers reflects differential access to carotenoid pigments at the time of molt (Brush and Power 1976, Hill 1992, in press a, b). Males from 4 different C. m. frontalis populations (brightly plumaged Michigan, California; drably plumaged California, Hawaii) responded to standardized diets in a similar manner. When they were fed a plain seed diet, which was fully nutritious but provides few carotenoid pigments, all males grew feathers with similar pale yellow coloration (Brush and Power 1976, Hill 1992, in press a). On a seed diet with ß-carotene added, all males grew pale orange feathers. And, on a seed diet with the red carotenoid canthaxanthin added, all males grew bright red feathers. Moreover, the variance in plumage coloration among males after treatment on a standardized diet was significantly lower than the variance in appearance among males from wild populations (Hill 1992). Female House Finches also converged on a similar plumage when their access to carotenoid pigments was standardized during molt (Hill in press b). Although relatively few wild females show detectable carotenoid pigmentation (see Distinguishing Characteristics), when canthaxanthin was added to their diets all females showed maximum female expression of carotenoids with a red wash on the rump, crown, and underside (Hill in press b).Unlike plumage coloration, the pattern of coloration is not dependent on diet. In controlled feeding experiments, C. m. griscomi males retained their small patches and C. m. frontalis males retained their medium patches regardless of their access to carotenoid pigments during molt, and a single hybrid male from a griscomi x frontalis cross displayed a patch size that was intermediate to the two parental types (Hill in press a).Hill, Geoffrey E. 1993. House Finch (Carpodacus mexicanus), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu.library...na/species/046