The Yellow-eyed Junco occurs in Transition and Boreal Zones in the mountains from the southwestern United States to Guatemala and is resident throughout much of its range. In southern Arizona and southwestern New Mexico, pairs maintain all-purpose breeding territories and then migrate to lower elevations and form winter flocks with the Dark-eyed Junco (Junco hyemalis). These relatively confiding birds forage on the ground and are easily seen, often frequenting campsites and picnic areas. In southern Arizona, pairs remain together throughout the breeding period, producing up to 3 successful broods per year. During the breeding period, males are often heard singing their multipart, warbler-like song from high atop conifers.
Yellow-eyed Junco is locally abundant, sedentary, and philopatric, and the species adapts well to captivity. These traits make it an exceptional species for behavioral studies, and its behavior and life history are reasonably well understood. Songs of the Yellow-eyed Junco, with their 2 to 3 parts and multiple trills, are highly variable within populations. This species was featured in classic studies on individual variation in song (1) and song development (2). A series of studies on the effects of flock size on behavior and individual trade-offs among foraging, vigilance, and aggression were based on winter flocks of the Yellow-eyed Junco in southern Arizona (3, 4, 5, 6). Growth, energy expenditure, and time allocation are well understood in this species from studies conducted over the annual cycle in southern Arizona (7, 8, 9, 10, 11, 12, 13). In most passerine species, young birds are difficult to find once they leave the nest, and consequently little is known about fledgling and juvenile life history stages. Studies on mortality patterns, acquisition of foraging skills, energy expenditure, and time allocation of immatures has made a valuable contribution to our understanding of fledging and juvenile passerines (14, 15, 16, 12, 7, 9, 10). To date, most studies of behavior, ecology, and physiology of the Yellow-eyed Junco have been carried out in southern Arizona at the northern extent of its range. It is not known whether these populations are representative of populations throughout the range of the species.