The Lesser Goldfinch is a small, social, seed-eating songbird that inhabits a wide variety of habitats of the western United States from Oregon east into Colorado and Texas, and south to Mexico. South of the United States, it is widespread through Mexico and Central America, and its range extends into northern and western South America. In the United States, it is common in California, Arizona, parts of New Mexico and Colorado and south-central Texas, the areas of highest population density, but less common and more locally distributed in other regions.
This species is generally found in small groups in open country with scattered trees, along western range foothills, and frequently in agricultural lands. Like many cardueline finches, it is often nomadic and sporadic in occurrence. In the last decade, regions of rapid expansion and population growth have centered on northern edges of its range where winter bird-feeding may assist its overwintering, and in developing areas of desert habitats such as in Arizona where residential housing and agriculture with irrigation and plantings may also be having favorable impacts on the species.
In general, this species is less well known than its congener the American Goldfinch (Spinus tristis), being less widely distributed in the United States, less abundant, and less studied. Much information available for the species is general and anecdotal and is often assumed to be similar to that known for the American Goldfinch. Like the American Goldfinch, the Lesser Goldfinch breeds in loosely colonial groups, defending territories only near its nest, and it seems to be monogamous during the breeding season, with the male feeding the female on the nest throughout incubation. In winter it congregates in foraging flocks, often with other cardueline finches. Throughout the year it feeds almost exclusively on seeds, mostly of composites. Its adaptability to a wide range of foods and habitats, including those modified by human activities, appears to have protected it from widespread population decreases during the recent past.
Notable characteristics of this species are its incorporation of other species' songs into the male song repertoire, and its geographic plumage polymorphism: Most western males (S. p. hesperophilus) have green backs, and most eastern males (S. p. psaltria) have black backs, although females do not differ in coloration. These types also exhibit different molt and breeding phenologies (Willoughby 2007).
The species has received limited scientific attention. Primary research papers dealing with Lesser Goldfinch biology include: observations of a nest ( Chambers 1915 ); a study of maintenance behaviors ( Coutlee 1968b ); comparative studies of breeding biology (Coutlee Coutlee 1966 , Coutlee 1968a ) and vocalizations ( Coutlee 1971 ) of Lesser and Lawrence's (Spinus lawrencei) goldfinches; analysis of vocal mimicry ( Goldwasser 1987 ); and inclusion in a study of genetic relationships of North American cardueline finches ( Marten and Johnson 1986 ). Linsdale's ( Linsdale 1957 ) detailed study of diet, ecology, and breeding of goldfinch species at Hastings Natural History Reservation in Monterey Co., CA, provided the information in A. C. Bent's life history series ( Linsdale 1968b ), as well as much of what is reported in this account for those topics. Gross ( Gross 1968c ) summarized traits of the eastern sub-species (psaltria) in A. C. Bent's life history series.
Recent work includes winter range expansion in Colorado, Utah and Nevada (Versaw 2000, 2001), breeding biology in Colorado (Prather et al. 2002), vocalization and song mimicry in Colorado (Kingery 2004), physical characteristics across the subspecific spectrum in the U.S. (Willoughby 2007), and mitochondrial DNA phylogenetics (Arnaiz-Villena et al. 2008). In addition, numerous breeding bird atlases and state bird books have come out since this account first appeared, expanding our knowledge of populations, ranges, and local preferences of the species.
Nonetheless, much work can still be done on 1) the nature of intergrading characteristics between the two supposed subspecies, psaltria in the east and hesperophilus in the west, where they both occur in Arizona and New Mexico, 2) the importance of human impacts -- habitat alteration and food and water provisioning -- on breeding and overwintering populations; and 3) the effects of age on male plumage coloration and song repertoire, to list just a few.