A multi-locus phylogeny suggests an ancient hybridization event between Campephilus and melanerpine woodpeckers (Melanerpes and Sphyrapicus) during the colonization of the New World (Fuchs et al., 2013).
Chialchia and Smith (2014) provide a detailed description of a hybrid between Cream-backed Woodpecker (Campephilus leucopogon) and Crimson-crested Woodpecker (C. melanoleucus), two species that co-occur along the banks of the Paraná River in Paraguay.
Hybridization between Yellow-shafted Flicker (C. auratus auratus) and Red-shafted Flicker (C. a. cafer) was discovered and discussed early on (Allen, 1892; Anderson, 1971; Deakin, 1936; Eaton, 1893; Rhoads, 1892). The situation was thoroughly described by Short (1965). Pairing among subspecies was found to be random (Bock, 1971; Moore, 1987). Genetic analyses showed a clear structure in mtDNA, but none in nuclear markers (allozymes), which pointed towards gene flow (Fletcher & Moore, 1992; Grudzien & Moore, 1986; Grudzien et al., 1987; Moore, Graham & Price, 1991). The hybrid zone was considered a “hybrid superiority zone” because the zone remained stable (Moore & Buchanan, 1985) and there was no difference in reproductive success between hybrids and pure individuals (Grudzien & Moore, 1986). However, certain populations did not follow these patterns. In Alberta, the hybrid zone was expanding (Mcgillivray & Biermann, 1987). And in the northern populations mating was non-random (Wiebe, 2000; Wiebe & Bortolotti, 2001). This raised the question whether phenotypic variation was related to survival. Further studies showed that carotenoid colour was not correlated with reproduction or survival (Wiebe & Bortolotti, 2002). Instead survival seemed to depend on large-scale weather patterns (Flockhart & Wiebe, 2007; Flockhart & Wiebe, 2008). Possibly, annual changes in selection pressures could mask fitness differences between phenotypes (Flockhart & Wiebe, 2009).
In addition to this well-studied hybrid zone, other Colaptes species are known to hybridize. For example, Red-shafted Flicker (C. a. cafer) and Gilded Flicker (C. chrysoides) in North America (Short, 1965) and several (sub)species in South America (Short, 1972).
Miller (1955) describes a hybrid between Hairy Woodpecker (D. villosus) and Ladder-backed Woodpecker (D. scalaris). And to study introgression between Great Spotted Woodpecker (D. major) and Syrian Woodpecker (D. syriacus) in Poland multiple molecular markers were developed (Gorman, 1997; Michalczuk et al., 2014).
A hybrid between Pale-headed Woodpecker (G. grantia) and Bamboo Woodpecker (G. viridis) from Thailand was described morphologically (Round et al., 2012).
This genus comprises four species: Red-naped Sapsucker (S. nuchalis), Red-Breasted Sapsucker (S. ruber), Williamson’s Sapsucker (S. thyroideus) and Yellow-bellied Sapsucker (S. varius), that all occur in North America (Howell, 1952). Hybrids between several of these species have been reported (Browning, 1977; Scott, Ankney & Jarosch, 1976; Short & Morony, 1970; Weisser, 1973). Red-naped and Red-breasted Sapsucker display low genetic distances, based on nuclear (Johnson & Zink, 1983) and mitochondrial markers (Cicero & Johnson, 1995). Hybrid zone analyses indicate selection against hybrids (Johnson & Zink, 1983; Seneviratne et al., 2016). Similarly, genetic and morphological analyses of the hybrid zone between Red-breasted and Yellow-bellied Sapsucker show signs of selection against hybrids (Seneviratne et al., 2016; Seneviratne et al., 2012). A genomic analyses of several hybrid zones showed that the tree species are clearly distinct with a small number of hybrids in each hybrid zone. This indicates that there is moderately strong reproductive isolation between them. There were no large regions of differentiation in the genome (so-called ‘genomic islands of differentiation’). However, the authors uncovered 19 small regions of differentiation, some of which were shared between species. One of those regions contained a candidate locus associated with plumage, which could contribute to reproductive isolation (Grossen et al., 2016).
Allen, J. A. (1892). The North American species of the genus Colaptes, considered with special reference to the relationships of C. auratus and C. cafer. order of the Trustees, American Museum of Natural History.
Anderson, B. W. (1971). Mans Influence on Hybridization in 2 Avian Species in South-Dakota. Condor 73, 342-&.
Bock, C. E. (1971). Pairing in Hybrid Flicker Populations in Eastern Colorado. Auk 88, 921-&.
Browning, M. R. (1977). Interbreeding members of the Sphyrapicus varius group (Aves: Picidae) in Oregon. Bulletin of the Southern California Academy of Sciences 76, 38-41.
Chialchia, A. O. C. & Smith, P. (2014). A notable hybrid woodpecker (Campephilus leucopogon x C. melanoleucus)(Aves: Picidae) from Paraguay. ORNITOLOGIA NEOTROPICAL 25, 459-464.
Cicero, C. & Johnson, N. K. (1995). Speciation in sapsuckers (Sphyrapicus) .3. Mitochondrial-DNA sequence divergence at the cytochrome-b locus. Auk 112, 547-563.
Deakin, A. (1936). Natural hybridization and genetics of flickers (Colaptes). American Naturalist, 585-590.
Eaton, A. A. (1893). Hybridism in Genus Colaptes. Science (New York, N.Y.) 21, 25-25.
Fletcher, S. D. & Moore, W. S. (1992). Further Analysis of Allozyme Variation in the Northern Flicker, in Comparison with Mitochondrial-DNA Variation. Condor 94, 988-991.
Flockhart, D. T. T. & Wiebe, K. L. (2007). The role of weather and migration in assortative pairing within the northern flicker (Colaptes auratus) hybrid zone. Evolutionary Ecology Research 9, 887-903.
Flockhart, D. T. T. & Wiebe, K. L. (2008). Variable Weather Patterns Affect Annual Survival of Northern Flickers More Than Phenotype in the Hybrid Zone. Condor 110, 701-708.
Flockhart, D. T. T. & Wiebe, K. L. (2009). Absence of Reproductive Consequences of Hybridization in the Northern Flicker (Colaptes Auratus) Hybrid Zone. Auk 126, 351-358.
Fuchs, J., Pons, J. M., Liu, L., Ericson, P. G. P., Couloux, A. & Pasquet, E. (2013). A multi-locus phylogeny suggests an ancient hybridization event between Campephilus and melanerpine woodpeckers (Ayes: Picidae). Molecular Phylogenetics and Evolution 67, 578-588.
Gorman, G. (1997). Hybridisation by Syrian Woodpeckers. BRITISH BIRDS 90, 578-578.
Grossen, C., Seneviratne, S. S., Croll, D. & Irwin, D. E. (2016). Strong reproductive isolation and narrow genomic tracts of differentiation among three woodpecker species in secondary contact. Molecular ecology 25, 4247-4266.
Grudzien, T. A. & Moore, W. S. (1986). Genetic Differentiation between the Yellow-Shafted and Red-Shafted Subspecies of the Northern Flicker. Biochemical Systematics and Ecology 14, 451-453.
Grudzien, T. A., Moore, W. S., Cook, J. R. & Tagle, D. (1987). Genic Population-Structure and Gene Flow in the Northern Flicker (Colaptes-Auratus) Hybrid Zone. Auk 104, 654-664.
Howell, T. R. (1952). Natural history and differentiation in the Yellow-bellied Sapsucker. Condor, 237-282.
Johnson, N. K. & Zink, R. M. (1983). Speciation in Sapsuckers (Sphyrapicus) .1. Genetic Differentiation. Auk 100, 871-884.
Mcgillivray, W. B. & Biermann, G. C. (1987). Expansion of the Zone of Hybridization of Northern Flickers in Alberta. Wilson Bulletin 99, 690-692.
Michalczuk, J., McDevitt, A. D., Mazgajski, T. D., Figarski, T., Ilieva, M., Bujoczek, M., Malczyk, P. & Kajtoch, L. (2014). Tests of multiple molecular markers for the identification of Great Spotted and Syrian Woodpeckers and their hybrids. Journal of Ornithology 155, 591-600.
Miller, A. H. (1955). A Hybrid Woodpecker and Its Significance in Speciation in the Genus Dendrocopos. Evolution 9, 317-&.
Moore, W. S. (1987). Random Mating in the Northern Flicker Hybrid Zone – Implications for the Evolution of Bright and Contrasting Plumage Patterns in Birds. Evolution 41, 539-546.
Moore, W. S. & Buchanan, D. B. (1985). Stability of the Northern Flicker Hybrid Zone in Historical Times – Implications for Adaptive Speciation Theory. Evolution 39, 135-151.
Moore, W. S., Graham, J. H. & Price, J. T. (1991). Mitochondrial-DNA Variation in the Northern Flicker (Colaptes-Auratus, Aves). Molecular Biology and Evolution 8, 327-344.
Rhoads, S. N. (1892). HYBRIDISM EXEMPLIFIED IN THE GENUS COLAPTES. Science (New York, N.Y.) 20, 325-7.
Round, P. D., Hobday, J. M., Kanjanavanit, R. & Steward, J. S. (2012). A nesting pair of Gecinulus woodpeckers in a likely zone of intergradation between Pale-headed Woodpecker G. grantia and Bamboo Woodpecker G. viridis. FORKTAIL, 113-120.
Scott, D., Ankney, C. D. & Jarosch, C. (1976). Sapsucker hybridization in British Columbia: changes in 25 years. Condor, 253-257.
Seneviratne, S. S., Toews, D. P. L., Brelsford, A. & Irwin, D. E. (2012). Concordance of genetic and phenotypic characters across a sapsucker hybrid zone. Journal of Avian Biology 43, 119-130.
Seneviratne, S. S., Davidson, P., Martin, K. & Irwin, D. E. (2016). Low levels of hybridization across two contact zones among three species of woodpeckers (Sphyrapicus sapsuckers). Journal of Avian Biology.
Short, L. L. (1965). Hybridization in the flickers (Colaptes) of North America. Bulletin of the AMNH; v. 129, article 4.
Short, L. L. (1972). Systematics and behavior of South American flickers (Aves, Colaptes). Bulletin of the AMNH; v. 149, article 1.
Short, L. L. & Morony, J. J. (1970). A Second Hybrid Williamson’s× Red-Naped Sapsucker and an Evolutionary History of Sapsuckers. Condor, 310-315.
Weisser, W. (1973). A mixed pair of sapsuckers in the Sierra Nevada. Western Birds 4, 107-108.
Wiebe, K. L. (2000). Assortative mating by color in a population of hybrid northern flickers. Auk 117, 525-529.
Wiebe, K. L. & Bortolotti, G. R. (2001). Variation in colour within a population of northern flickers: a new perspective on an old hybrid zone. Canadian Journal of Zoology-Revue Canadienne De Zoologie 79, 1046-1052.
Wiebe, K. L. & Bortolotti, G. R. (2002). Variation in carotenoid-based color in Northern Flickers in a hybrid zone. Wilson Bulletin 114, 393-400.