There are two color forms of the Northern Flicker (Colaptes auratus), the “Yellow-shafted” of east of the Rocky Mountains (C. a. auratus, hereafter YSFL) and the “Red-shafted” of west of the Rockies (C. a. cafer, RSFL). The most obvious difference is the flight feathers (wings and tail): YSFL have yellow shafts and undersides to these feathers, while the RSFL’s are red. RSFL also lack the red patch on the nape present in YSFL, have brown rather than gray crowns, and gray rather than tan throats. Male RSFL have red “mustaches” while male YSFL have black ones.
A stable hybrid zone extends along the east slope of the Rockies from southern Alaska to the Texas panhandle. Here, these two forms freely interbreed. Resulting offspring can show a wide variety of traits, including a number of combinations of traits of either or both parents, or intermediate forms of individual traits.
Occasionally, hybrids (more correctly, intergrades) wander out of range. On 9 Oct 2002, RRBO captured one of these intergrades.
The paper below goes into more depth on the dynamics of the two color forms of flickers, the occurrence of intergrades in Michigan, and the interesting pattern of how these intergrade color forms then to be expressed:
Craves, J. A. 2002. Northern “Yellow-shafted” Flicker (Colaptes auratus) with red feathers banded in Wayne Co., MI. (pdf) Michigan Birds and Natural History 9:199-205.