Rosy-finches breed at the highest altitude of any species north of the Mexican border in North America, usually nesting on cliffs overlooking glaciers and snowfields on the highest peaks, and above the meadows and tundra frequented by other alpine bird species. The Brown-capped Rosy-Finch is the southernmost of 3 closely related species on this continent and has the smallest distribution, being almost endemic to Colorado. It is also the most distinctive, with rosy colors covering more of its body than in other species and lacking the clear gray color on the head that is so characteristic of the other species. It is also the most sexually dimorphic in color.
In summer, this species is most frequently seen foraging on insects frozen on the surface of snowfields and on seeds exposed along the retreating margins of the snow. In winter, severe storms and deep snow drive individuals down to lower altitudes, where they are seen in large flocks along the snow-free margins of roads, on phone wires, and at feeders. At night, they roost in old Cliff Swallow (Petrochelidon pyrrhonota) nests, barns, and caves that provide protection from winter cold. But even in the coldest of winters, they seem to prefer the highest altitudes where food can be found, and will commute on a daily basis up to alpine tundra when temperatures are –35°C if winds have exposed portions of the tundra and ridges for feeding.
The breeding biology of this species is unusual in that males primarily defend a floating territory around their mates, rather than around a fixed piece of alpine real estate. This is thought to result from a skewed sex ratio with females in short supply, but the questions of mating systems, sex ratios, and the possible role of nonbreeding males all deserve further study.
Due to the relative inaccessibility of the alpine habitat generally and nesting cliffs in particular, few studies have focused on this species, and much of the published information is scattered and anecdotal. Perhaps the most important early advance was the discovery of the first nest in 1915 by F. C. Lincoln (Lincoln 1916). There followed a period (1916–1930s) of egg collecting by Lincoln, W. C. Bradbury, F. W. Miller, and A. T. Wheeler, which, though unpublished at the time, provided the early basis for understanding the breeding biology of the species. Other important contributions were those of Davis (Davis 1960a) on several nests in the Mosquito Range of Colorado, A. M. Bailey and R. J. Niedrach's massive compendium of the Birds of Colorado (1965) in which they report their observations on nests near Loveland Pass, and Packard's (Packard 1968) summary of information over the entire range of the species. Major contributions since that time include D. L. Pattie and K. B. Hunter's 3-year study (1967–1969) of nesting and nutritional ecology (reported here for the first time), range extensions and breeding behavior by Hendricks (Hendricks 1977, Hendricks 1978, Hendricks 1980b, this account), work on systematics, foraging, and winter ecology by Johnson (Johnson 1972d, Johnson 1977b, this account), and the behavioral studies by Shreeve (Shreeve 1977, Shreeve 1980a). Together with the abundance of anecdotal information, these studies flesh out the broad outlines of the biology of the Brown-capped Rosy-Finch, and clarify the areas where more study is needed.