The Northern Flicker is a common, primarily ground-foraging woodpecker that occurs in most wooded regions of North America. Its taxonomic status has been debated because of hybridization among subspecies groups, each readily distinguished by plumage coloration. Two subspecies, the Yellow-shafted Flicker (Colaptes auratus auratus) of eastern North America and the Red-shafted Flicker (C. a. cafer) of western North America, form a long, narrow hybrid zone in the Great Plains that parallels the rain shadow of the Rocky Mountains and crosses the Canadian Rockies extending to southern Alaska. This hybrid zone has been of great interest to ornithologists and evolutionary biologists for more than a century. Hybridization occurs on a more limited basis between the "Red-shafted" Flicker and the Gilded Flicker (C. chrysoides), a separate species associated with the Sonoran Desert. Two other subspecies groups of the Northern Flicker are allopatric; the Cuban Flicker (chrysocaulosus Group) occurs on Cuba and Grand Cayman Island, and the Guatemalan Flicker (mexicanoides Group) occurs in the highlands of southern Mexico south to northwestern Nicaragua.
The subspecies differ in several bright and contrasting plumage traits, the most obvious being the shaft color of flight feathers, from which the two North American subspecies derive their common names. The bright yellow or red colors visible on the undersurface of the wings are flashed at potential mates or rivals during courtship and territorial defense. Other traits that distinguish the subspecies are the presence of a bright red nuchal (nape) patch in the Yellow-shafted and Cuban flickers (absent in others) and the color of the throat, ear coverts, crown, and malar stripe. The malar stripe, or “mustache,” is the only markedly dimorphic trait that distinguishes the sexes.
As its broad geographic distribution suggests, the Northern Flicker is a generalist in many respects, but in others it is a specialist. It is clearly a species of open woodlands, savannas, farmland with tree rows, and forest edges. It eats mostly ants but also beetle larvae and—during late autumn, winter, and early spring—a variety of berries. The Northern Flicker is well adapted to habitats altered by humans, commonly breeding in urban as well as suburban and rural environments, and visiting backyard bird feeders. Nevertheless, data from the North American Breeding Bird Survey indicate significant declines in abundance. Reasons for these declines are unclear, but likely explanations are habitat loss and competition with the European Starling (Sturnus vulgaris) for nest cavities. Although the Northern Flicker remains abundant, this declining trend should be viewed with concern because the species plays a central role in the ecology of woodland communities where it excavates many of the cavities later used by other hole-nesting species.
Early research on the Northern Flicker focused on phenotypic variation and dynamics of the hybrid zone. The detailed and descriptive work of Lester Short (Short 1965b, Short 1967b), who studied flickers in the central United States, was followed by more quantitative models of dispersal, gene flow, and reproductive success of flickers in the hybrid zone (e.g. Moore 1987b, Moore and Price 1993). Many researchers have reported on aspects of behavior and nest use by Northern Flickers as part of general studies of cavity-nesting birds. Recently, such interest has intensified as flickers have been recognized as "keystone" excavators that may influence the abundance of secondary cavity-nestering species in forest systems (Martin et al. 2004a). The largest study dedicated to understanding the reproductive ecology, life history, and population ecology of the Northern Flicker is a long-term study by K. L. Wiebe at Riske Creek, central British Columbia, where 100–150 color-banded nesting pairs have been monitored annually since 1997.