Generally an inhabitant of coniferous or mixed coniferous-deciduous forests, the Pine Siskin breeds as far north as central Alaska and northern Canada but also ranges south in suitable habitat to northern Baja California and through the Mexican highlands to Guatemala. Known to many observers as an unpredictable winter visitant, it is an irruptive species abundant in a given locality one year and often absent the next. Presumably this pattern is related in some way to annual variation in the distribution and abundance of seeds that make up the bulk of its diet. Reproductive schedule and attachment to a particular breeding area appear to be less rigidly fixed in the Pine Siskin than in many other songbirds. In some cases, members of an irruptive population may linger on a favorable wintering ground long enough to breed.
The opportunistic nature of the species and its partial indifference to constraints of time and space make it an intriguing subject for a variety of studies. Most accounts of it are anecdotal. However, important information is available from studies in California, New Hampshire, and Nebraska ( Rodgers 1937 , Weaver and West 1943 , Perry 1965 ) concerning phenology, nesting, parental behavior, and development of young. The species is featured prominently in analyses of irruptive movements of seed-eating boreal birds ( Bock and Lepthien 1976f ), and a study of Michigan individuals reveals impressive resistance to cold ( Dawson and Carey 1976 , Dawson and Marsh 1986 ). In addition, banding studies in New York (Yunick Yunick 1976a , Yunick 1977d , Yunick 1983c , Yunick 1992b , 2003, 2005) provide valuable data concerning winter site fidelity and maturation patterns. For the future, studies of orientation, migratory physiology, and reproductive and population biology should prove especially rewarding.