Flickers are medium-sized woodpeckers found throughout most of North America. They are known for their bright yellow or red wing linings that are visible during flight. There are two distinct color variants – the yellow-shafted flicker which has bright yellow wing linings, and the red-shafted flicker which has bright red wing linings. The color difference led to them being considered separate species for many years.
Quick Answer
Red and yellow-shafted flickers are now considered to be two color morphs of the same species, Colaptes auratus. They freely interbreed in areas where their breeding ranges overlap and produce offspring of intermediate color. Genetic studies have confirmed they are a single species. The color difference is caused by a single gene that controls carotenoid pigment deposition in the feathers.
Geographic Ranges
Yellow-shafted flickers are found in eastern North America from the Atlantic coast to the Great Plains, while red-shafted flickers occupy western North America from the Rocky Mountains to the Pacific coast. There is a broad overlap zone centered along the eastern edge of the Great Plains where both color morphs occur. East of the Appalachians, nearly all flickers are yellow-shafted. West of the Rocky Mountains, nearly all are red-shafted. Within the Great Plains overlap zone, a mix of both morphs is present.
Yellow-shafted Range
The yellow-shafted flicker occupies the eastern half of North America, ranging:
- From Newfoundland to Florida in the east
- As far west as eastern Texas, Oklahoma, and Kansas
- North to central Alberta, central Saskatchewan, central Manitoba, Ontario, Quebec, and New Brunswick
Red-shafted Range
The red-shafted flicker occupies the western half of North America, ranging:
- From Alaska and western British Columbia south to northwest Mexico
- As far east as western Texas, western Oklahoma, western Kansas, western Nebraska, and western North Dakota
Physical Differences
The most obvious difference between red and yellow-shafted flickers is the color of the wing and tail feathers. In flight, this color difference is very noticeable:
- Yellow-shafted flickers have bright yellow wing linings and black tail feathers with yellow shafts.
- Red-shafted flickers have bright red wing linings and black tail feathers with red shafts.
Some other subtle physical differences include:
Trait | Yellow-shafted | Red-shafted |
---|---|---|
Bill color | Black | Grayish or greenish |
Belly color | Pale brownish | Pinkish |
Throat color | Brown | Gray |
Nape color | Olive-brown | Grayish |
However, all of these subtle differences overlap between the morphs and are not diagnostic. The wing and tail feather color is the only reliable way to identify the morphs.
Genetic Basis
The genetic basis of the color difference in flickers was uncovered in the late 1990s. A single gene was found to control the yellow versus red color of the wing and tail feathers. This gene codes for an enzyme called carotenoid ketolase that is involved in the production of red ketocarotenoid pigments. The gene comes in two variants:
- The Y allele produces normal levels of ketolase for red pigment production.
- The y allele produces a non-functional ketolase, resulting in yellow pigment deposition.
Red-shafted flickers have two copies of the Y allele (genotype YY). Yellow-shafted flickers have two copies of the y allele (genotype yy). Birds with one of each allele (Yy) have an intermediate orange color.
Evidence of Interbreeding
There is overwhelming evidence that red and yellow-shafted flickers interbreed freely where their breeding ranges meet in the Great Plains overlap zone:
- Both morphs nest side-by-side in the overlap zone.
- Pairs containing one red-shafted and one yellow-shafted flicker are common.
- Many hybrid intermediates occur showing mixed red and yellow feather coloring.
- The intermediate hybrid zone shifts over time but remains centered on the Great Plains.
The presence of a broad hybrid zone with birds showing all gradations of color provides definitive evidence the two forms interbreed extensively when in contact. This level of interbreeding only occurs between members of the same species.
Genetic Analyses
Genetic studies of flickers have confirmed red and yellow-shafted birds are a single interbreeding population:
- Mitochondrial DNA analyses found complete overlap between the morphs with no distinct lineages.
- Nuclear DNA analyses also found complete overlap and mixing of alleles.
- No fixed genetic differences were found between the morphs at any loci.
The genetic evidence clearly shows there are no reproductive barriers between the color morphs. They form a continuous intermixing and interbreeding population connected by gene flow. This genetic cohesion across their entire range proves they are the same species.
Vocalizations
The vocalizations of flickers also support them being the same species. There are some subtle average pitch differences between the morphs, but call note structure is identical:
- The advertising call is a loud repeated rolling sound, often described as “wik-wik-wik-wik”.
- The alarm call is a loud piercing “kleeer!” or “cleeear!”.
- The song is a soft mellow cooing, “coo-coo-coo”.
There is extensive overlap in vocalizations between morphs because calls are learned from parents and neighbors. The nearly identical vocal repertoires reflect their close evolutionary relationship.
Taxonomic Treatment
Based on the overwhelming evidence of interbreeding and genetic cohesion, the American Ornithologists’ Union lumped red and yellow-shafted flickers into a single species, Colaptes auratus, in 1995. They are now recognized as two color morphs rather than separate species. Some key points:
- The two morphs freely interbreed where their ranges meet.
- There are no fixed genetic differences between the morphs.
- All characteristics, other than feather color, overlap extensively.
- They behave as a single coherent breeding population.
This treatment as a “polytypic species” with multiple color morphs is well supported by all available evidence. Considering them separate species does not fit with our modern biological understanding of what defines a species.
Conclusion
In conclusion, red and yellow-shafted flickers are two color variants of the same species based on extensive interbreeding, lack of fixed differences, complete genetic cohesion, and near identical behavior and vocalizations. The distinct red and yellow feather coloring is controlled by a single gene that regulates carotenoid pigment deposition. Their recognition as separate species for over a century represented a mistaken taxonomic treatment that has now been conclusively overturned by modern evidence.