Galliformes – or wildfowl – are heavy-bodied ground-feeding birds that include familiar species, such as Turkey, Chicken and Pheasant. Hybridization is a common phenomenon is this bird group.

Alectoris

There are several species of Alectoris partridges, distributed across Eurasia and Africa (Watson, 1962). Some species live in sympatry and hybridize naturally, while other species have been introduced in the range of other for hunting purposes and also hybridize. However, domesticated birds seem to have a lower survival rate (Duarte & Vargas, 2004). Four species pairs have been studied. The Sardinian Partridge (A. barbara) does not appear to interbreed with other species (Scandura et al., 2010), although markers to detect hybridization have been developed (Barbanera et al., 2011b).

The Red-legged Partridge (A. rufa) and the Rock Partridge (A. graeca) overlap in the southern Alps. The hybrid zone cline is shorter than expected which could point to selection against hybrids (Barilani et al., 2007a; Randi & Bernard-Laurent, 1999). Rock Partidges have also been introduced outside of their natural range into the Iberian peninsula where they also hybridize with native Red-legged Partridges (Negro, Torres & Godoy, 2001). The call characterists of both species and their hybrids have been studied (Ceugniet et al., 1999) and playback experiments reveal similar reactions to conspecific and hybrid calls, however, hybrids responded stronger to hybrid calls (Ceugniet & Aubin, 2001).

The Red-legged Partridge also interbreeds with the introduced Chukar Partridge (A. chukar) (Barbanera et al., 2010); introgression has been detected in Italy (Baratti et al., 2005; Barbanera et al., 2007; Barbanera et al., 2009; Barbanera et al., 2005; Negri et al., 2013), Iberia (Blanco-Aguiar et al., 2008; Martinez-Fresno, Henriques-Gil & Arana, 2008; Sevane et al., 2011; Tejedor et al., 2007), France (Barbanera et al., 2009) and the United Kingdom (Barbanera et al., 2015). The population of Red-legged Partridges on Corsica seems to be non-introgressed (Barbanera et al., 2011a). Genomic analyses confirmed these patterns, but indicated that introgression is quite limited across the range of the Red-legged Partridge (Forcina et al., 2021).

Studies on the fitness of these hybrids showed that hybrids have bigger clutch sizes but lower hatching success and survival rates compared to pure individuals (Casas et al., 2012) and that male hybrids are smaller while female ones have a better condition but lower carotenoid level (Casas et al., 2013).

The Chukar Partrigde also hybridizes with other species, such as the Rock Partrigde in Greece (Barilani et al., 2007b) and Italy/France (Barilani et al., 2007a) and the Przevalski’s Partridge (A. magna) in China (Chen et al., 1998; Huang et al., 2009; Yang & Liu, 2009).

Chrysolophus

On a nearly 900-year-old Chinese painting, a hybrid between Golden Pheasant (C. pictus) and Lady Amherst’s Pheasant (C. amherstiae) is depicted (Peng et al., 2016).

Coturnix

The Common Quail (C. coturnix) and the Japanese Quail (C. japonica) hybridize naturally in Russia, but the main concern is the release of domesticated Quail, which often carry “Japanese genes” (Sanchez-Donoso et al., 2012), in European populations of Common Quail (Amaral et al., 2007; Barilani et al., 2005; Chazara et al., 2010). Despite the release of these birds, the population size of Common Quail does not seem to be affected (Puigcerver, Sarda-Palomera & Rodriguez-Teijeiro, 2012; Puigcerver, Vinyoles & Rodriguez-Teijeiro, 2007). Hybrids do not differ in fertility or hatching success (Chang et al., 2009; Deregnaucourt, Guyomarc’h & Aebischer, 2002), but do show lower survival rates and suffer more from nest predation (Puigcerver et al., 2014), which could explain the limited effect of restocking. Interbreeding could however impact the migratory behavior of Common Quail. Experimental studies have shown that hybrids lose their tendency for migration (Deregnaucourt, Guyomarc’h & Spano, 2005; Deregnaucourt, Gyomarc’h & Belhamra, 2005). Restocked individuals were also not associated with migratory and wintering quails at northern latitudes (Sanchez-Donoso et al., 2014). The calls of both quail species and their hybrids have been heavily studied (Collins & Goldsmith, 1998; Deregnaucourt, 2010; Deregnaucourt, Guyomarc’h & Richard, 2001). One study found that Japanese Quails respond equally to conspecific, heterospecific and hybrid calls, which could lead to hybridization (Deregnaucourt & Guyomarc’h, 2003).

The egg production of hybrids between Japanese Quail and Brown Quail (C. ypsilophora) have also been investigated in an experimental setting (Vali, 2007).

Gallus

This genus, known as Junglefowl, contains four species: Sri Lanka Junglefowl (G. lafayetti), Grey Junglefowl (G. sonneratii), Green Junglefowl (G. varius), and Red Junglefowl (G. gallus). The latter species is probably the ancestor of the domestic chicken (Brisbin & Peterson, 2007; van Grouw, & Dekkers, 2020), although there has been gene flow from the other species (Lawal et al., 2020). For example, the gene that provides domestic chickens with their yellow skin was probably acquired through hybridization with Grey Junglefowl (Eriksson et al., 2008). Domestic chickens are regularly crossbred, as exemplified by a genetic study in Africa (Leroy et al., 2012). A phylogenetic study revealed that hybridization has also occurred between Grey Junglefowl and Red Junglefowl, and between Grey Junglefowl and Sri Lanka Junglefowl (Nishibori et al., 2005). The former cross has been described in captvity (Morejohn, 1968). On the Hawaiian island Kauai, escaped feral chickens are probably the result of hybridization between Red Junglefowl from Polynesia and recently escaped domestic chickens from Europe (Gering et al., 2015). Similarly, in Singapore, there has been introgression between wild Red Junglefowl and feral chickens (Wu et al., 2020).

Domestic chickens have also been crossed experimentally with Helmeted Guineafowl (Numida meleagris) (Leroy, Barbier & Auzanneau, 1908; Leroy, Barbier & Auzanneau, 1967) and Pheasant (Phasianus colchicus) (Castillo et al., 2012; Castillo et al., 2010).

Several Chinese indigenous chicken breeds have been genetically “polluted” by commercial broilers (Zhang et al., 2019; Nie et al., 2019).

The Ecuadorian Creole chicken probably originated from Asian birds that were brought to Chile in pre-Columbian times. Later, the introduction of Spanish breeds by the conquistadors in the 15th century led to several admixture events (Toalombo Vargas et al., 2019).

Lagopus

One experimental study described the effects of increasing daylength om Willow Grouse (L. lagopus) and Red Grouse (L. l. scoticus) and their hybrids (Sharp & Moss, 1981). Introgression between Willow Grouse and Rock Ptarmigan (L. muta) occurs in Central Sweden (Quintela, Thulin & Hoglund, 2010).

Lophura

The Gallopheasants are classified into ten species (Randi et al., 2001). The extinct Imperial Pheasant (L. imperialis) turned out to be a occasional hybrid between Silver Pheasant (L. nycthemera) and Edwards’s Pheasant (L. edwardsi), one specimen was probably even a hybrid between Silver Pheasant and Vietnamese Pheasant (L. hatinhensis) (Hennache et al., 2003). A phylogeographic study uncovered hybridization between Silver Pheasant and Kalij Pheasant (L. leucomelanos) in China (Dong et al., 2013).

Meleagris

Wild Turkeys (M. gallopavo) hybridize extensively with introduced subspecies in Texas (Latch et al., 2006).

Numida

The Helmeted Guineafowl (N. meleagris) has been crossed with other galliform species, such as the domestic chicken (Gallus gallus) (Beddard, 1899; Guyer, 1909; Kalla, Danladi & Dass, 2008; Leroy et al., 1908; Leroy et al., 1967; Morton, 1847; Vilaró Díaz, 1897). The latter hybrid is still used in other research areas (Liu & Zhu, 2008; Mathis & McDougald, 1987). There is also hybridization between wild and domesticated Guineafowl (Walker et al., 2004).

Genetic analyses of a putative hybrid between Helmeted Guineafowl and Brazilian Guan (Penelope superciliaris) (Ruschi & Amadon, 1959) revealed that it was actually a hybrid between Helmeted Guineafowl and Chicken (Alfieri et al., 2023).

Odontophoridae

The New World Quails is an American bird family which comprises several genera. Hybrids within (Bailey, 1928; Banks & Walker, 1964; Cink, 1975; Hubbard, 1966) and between genera (McCabe, 1954; Peck, 1911; Sutton, 1963) have been documented, and summarized by Johnsgard (1970), who also conducted an experimental study on hybridization among Odontophoridae (Johnsgard, 1971).

Hybridization between Califoria Quail (Callipepla californica) and Gambel’s Quail (C. gambelii) has been documented in the past (Henshaw, 1885). The hybrid zone between these species was studied extensively by Jennifer Gee (Gee, 2003a). Using microsatellites (Gee, Calkins & Petren, 2003), she showed that the hybrid zone is located on a cline, and that introgression does not occur beyond this zone (Gee, 2004). Species discrimination is possible in captivity, but in nature breeding is random (Gee, 2003b). Social network analyses suggest that birds pair up based on body mass and monomorphic (i.e. the same in both sexes) plumage traits (Zonana et al., 2019) and mate randomly with regard to genetic ancestry (Zonana et al., 2020). Acoustical signals might be important in this context (Gee, 2005; Gee, Tomaszycki & Adkins-Regan, 2009).

Pauxi

The Alagoas Curassow (P. mitu) is extinct in the wild. To conserve this species it has been crossed with Razor-billed Curassow (P. tuberosa) (Silveira, Olmos & Long, 2013; Sousa et al., 2013; Wajntal, Pereira & Grau, 2010).

Phasianus

The is only one species of Pheasant (P. colchicus), which is subdivided into numerous subspecies that interbreed (Zhang et al., 2014). Hybrids between Sichuan Pheasant (P. c. strauchi) and Ring-necked Pheasant (P. c. torquatus) showed increased survival which resulted in a higher number of chicks per season (Niewoonder, Prince & Luukkonen, 1998). Hybrid pheasants were also more likely to establish themselves, a phenomenon dubbed “catapult effect” (Drake, 2006).

Pheasants have also hybridized with domestic chickens (Castillo et al., 2010; Castillo et al., 2012) and there is a record of a wild hybrid involving Dusky Grouse (Dendragapus obscurus) (Anthony, 1899).

Perdix

The effect of released Grey Partridges (P. perdix) on native populations has been investigated in Denmark (Andersen & Kahlert, 2012) and Finland (Liukkonen, Kvist & Mykra, 2012). In both cases, introduced birds were significantly different from wild ones.

Tetrao

The behavior (Porkert, Solheim & Flor, 1997) and sperm characeteristcs (Ciereszko et al., 2009) of hybrids between Black Grouse (T. tetrix) and Capercaillie (T. urogallus) have been described. Relatively unsuccessful attempts to cross Capercaillie with chicks have been conducted (Skjervold & Mjelstad, 1992).

Tetraogallus

Several genetic studies suggested hybridization between the Tibetan Snowcock (Tetraogallus tibetanus) and the Himalayan Snowcock (T. himalayensis) in Asia (An et al., 2020; Ding et al., 2020)

Tympanuchus

This genus of Prairie Chickens comprises three species that all hybridize, for instance Greater (T. cupido) Prairie Chicken hybridizes with Lesser Prairie Chicken (T. pallidicinctus) (Bain & Farley, 2002) and Sharp-tailed Grouse (T. phasianellus) (Lumsden, 2005a; Lumsden, 2005b). Introgression between these species has been confirmed by genetic analyses (Galla & Johnson, 2015). In addition, intergeneric hybrids have been reported:

• Sharp-tailed Grouse and Greater Sage Grouse (Centrocercus urophasianus) (Aldridge, Oyler-McCance & Brigham, 2001; Eng, 1971)
• Sharp-tailed Grouse and Dusky Grouse (Dendragapus obscurus) (Brooks, 1907; Lincoln, 1950; O’Donnell, 2015)

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