Striking in appearance and enigmatic in behavior, the Lawrence's Goldfinch is distinctive in many respects. As a breeding species, it is endemic to arid woodlands in the foothills of California and northern Baja California. In year-to-year movements, it seems more erratic than other goldfinches, and, unlike most passerines, it shows little loyalty to former breeding sites. On this habit of the species, Ralph Hoffman wrote: “A valley in southern California may be filled with the black-chinned, gray-bodied birds one summer and the next year contain not one” (Hoffman 1927: 309). At other times of the year, its behavior is just as mercurial. In some winters, for example, the species irrupts through Arizona, New Mexico, northern Mexico, and even into western Texas, yet in other winters, it is virtually absent from those areas. Sometimes it seems to disappear from most of its breeding range without reappearing elsewhere.
At least in California, the species exhibits a special predilection for seeds of native plants and may feed largely on the those of fiddleneck (Amsinckia spp., Boraginaceae) in summer and chamise (Adenostoma fasciculatum, Rosaceae) in winter. The kind and amount of such seeds have an important influence on this species' patterns of regional distribution and abundance. Lawrence's Goldfinch favors hotter and drier situations for nesting than other goldfinches, but its breeding sites are usually close to water, which it needs for drinking and bathing. Both Davis 2001d and Unitt 2004c stress that timing and location of nesting depend on rain and seed availability and that the species’ irregular occurrence in both breeding and non-breeding seasons is due to a strategy of opportunism. An examination of Christmas Bird Count data in California and Arizona suggests that high counts in both states follow years of high productivity followed by years of lower productivity, rather than high counts in Arizona coming from birds leaving California (D. Watt, unpublished data).
Some surprising new research led to the discovery that the brightening of male plumage as breeding season advanced is accomplished by feather wear (Willoughby et al. 2002) rather than a prealternate molt as previously reported (Pyle et al.1997, Davis 1999). Two mechanisms are responsible for the relative change in male and female breast coloration. First, yellow male breast feathers themselves are more resistant to wear than the surrounding gray feathers; thus the yellow patch size appears to enlarge as the season advances and gray feathers become worn. In addition each yellow male breast feather loses its brownish barbules, leaving only the yellow rachilla (Figure 11); thus the patch becomes brighter yellow in coloration. These rachillae are also larger in diameter (Figure 11) contributing to their relative strength. In contrast, female breast feathers all wear equally and uniformly (Figure 11) producing an increasingly duller coloration that increases relative sexual dichromatism. Males also develop more yellow coloration on the back, not present in females, due to brownish tips of these dorsal feathers wearing off exposing yellow proximal parts of the feathers, a different mechanism than the one that produces brighter breast patches. The diversity in molt patterns and sexual dichromatism patterns among the three North American goldfinches and their closest relative the Pine Siskin (Spinus pinus) was used by Willoughby (Willoughby 2004) to comment on controversies regarding molt terminology relative to homologous relationships among species. Feather wear to accomplish breeding season dichromatism in Lawrence’s Goldfinch is unique among these four species and appears to have evolved independently.
The male Lawrence's Goldfinch is an accomplished mimic, incorporating a variety of songs and calls from its foothill neighbors into its own rapid melody of wheezy whistles and tinkling, bell-like notes. The species is gregarious throughout the year, forming large flocks during winter and smaller feeding groups during the nesting season. The strong flocking tendency in this species leads some birds to follow a pair to its nest, where they are sometimes tolerated and other times chased off by the nesting pair. Pairs usually nest solitarily, but their inconsistent intolerance of conspecifics occasionally leads to the formation of loose colonies of up to ten or more pairs. Whether nesting solitarily or colonially, its small territory is generally weakly defended.
The species was described and named in 1850 by John Cassin for George Lawrence, a New York businessman and ornithologist. Cassin's dedication included the following: “I have named this bird in honor of Mr. George N. Lawrence, of the city of New York, a gentlemen whose acquirements, especially in American Ornithology, entitle him to a high rank amongst naturalists, and for whom I have a particular respect, because, like myself, in the limited leisure allowed by the vexations and discouragements of commercial life, he is devoted to the more grateful pursuits of natural history” (Cassin 1850b).
Although the peculiarities of the Lawrence’s Goldfinch make it an interesting subject for study, few studies have been conducted, perhaps because of the difficulties associated with its limited range and irregular occurrence. A few early investigations, however, provided important information on nesting habits, diet, behavior, and vocalizations during the breeding season (Linsdale 1950, Linsdale 1957, Coutlee 1968a, Coutlee 1968b). This account relies heavily on these few, but detailed, studies. Additional research is needed on the species' movement behavior and population ecology. It is still not clear if significant numbers of Lawrence's Goldfinches overwinter south of the U.S. in Sonora, Mexico, and whether patterns of migration should be considered true migration or irruptive movements.