Geographic Variation
Body size varies clinally, with birds in the north (Alaska and w. Canada) larger than those in the south (s. Arizona and n. Mexico). Wing and tail length vary the most among populations, whereas bill size and tarsus length vary little (Behle 1976). Southern birds have the forehead patch darker (most chestnut, less buff or white). Throat color varies from dark chestnut in the north to pale tawny in the south. Rump patches and underparts tend to be whiter in the north, whereas to the south birds often have the flanks tinged with rust or rufous (Behle 1976).
Subspecies
Four subspecies, following Phillips (1986), diagnosed chiefly on the coloration and pattern of the plumage on the head and on body size. Distinguishing characters listed below are for an adult with unworn plumage.
P. p. pyrrhonota (Vieillot, 1807). Includes Hirundo albifrons Rafinesque, 1822; P. lunifrons (Say, 1823); Hirundo opifex De Witt Clinton, 1824; H. republicana Audubon, 1824; P. p. hypopolia Oberholser, 1920; and P. p. aprilophata Oberholser, 1932 (see Browning 1992). Breeds across n. North America, from n. Alaska east through central Canada to the Maritimes and ne. United States and south; in the West, to nw. Baja California, n. Nevada, and central Colorado; and in the East, from the Ohio Valley, Chesapeake Bay, and (less commonly) to se. United States and the Gulf coast; winters south to central Argentina [type locality = Paraguay]. Throat and cheeks dark chestnut; forehead pale buff or whitish; rump chestnut; large (wing chord > 105 mm).
P. p. ganieri Phillips, 1986 (see Browning 1990). Breeds west of the Appalachians from (probably) s. Oklahoma south through central Texas to s. Texas and east to w.-central Tennessee [type locality = Kerr Co., Texas]; winter range unknown. Like P. p. pyrrhonota, but forehead darker buff; averages smaller (wing chord 102–108 mm; Phillips 1986).
P. p. tachina Oberholser, 1903. Breeds from central California east through s. Nevada to sw. Utah and south through the Lower Colorado River valley to ne. Baja California and east through central Arizona and New Mexico to sw. Texas [type locality = Langtry, Val Verde Co., Texas]; apparently winters south to n. Argentina (Phillips 1986). Similar to P. p. pyrrhonota, but throat and cheeks paler, forehead brownish buff, and chestnut rump darker; averages markedly smaller overall (wing chord < 108 mm).
P. p. melanogaster (Swainson, 1827). Includes Hirundo coronata Lichtenstein, 1831; P. p. swainsoni Sclater, 1858; and P. p. minima van Rossem and Hachisuka, 1938. Breeds from extreme se. Arizona and sw. New Mexico south over the Mexican plateau to Oaxaca and the Pacific plains to Nayarit [type locality = central Mexican Plateau]. Similar to P. p. tachina, but forehead dark chestnut. The ranges of tachina and melanogaster overlap in parts of se. Arizona, and both were found in the same colony near Fairbank, AZ (Jeter 1959).
Related Species
Monophyly of the Hirundinidae, the swallows and martins, has never been questioned, but relationships within the subfamily Hirundininae—a subfamily that includes all but the two species of river martins (Pseudochelidoninae)—have been difficult to tease apart. On the basis of behavior and basic morphology (i.e., ignoring sexually selected traits such as elongated rectrices), the genus Hirundo formerly included a large group of swallows that generally are blue dorsally, white and rufescent ventrally, and build their nests out of mud (Turner and Rose 1989). This treatment changed with the advent of molecular phylogenetics, such that Hirundo was split into three core genera: Hirundo sensu stricto (which includes the familiar Barn Swallow, H. rustica), Cecropis (the striated or red-rumped swallows), and Petrochelidon (the cliff swallows), although this taxonomic split had been recognized earlier by some authorities (e.g., Ridgway 1904, Peters 1960). The genera Delichon (the house martins) and Ptyonoprogne (the crag martins) round out this mud-nester clade (Sheldon et al. 2005). Despite Petrochelidon and Cecropis being lumped with Hirundo in various earlier works, it is actually Ptyonoprogne that is sister to Hirundo, whereas Petrochelidon and Cecropis are sister to each other and together are closest to Delichon (Sheldon et al. 2005).
The nearest living relative in North America of P. pyrrhonota is P. fulva, the Cave Swallow (Sheldon et al. 2005). Formerly little breeding sympatry, but these species have come into contact in Texas as bridges and highway culverts have been constructed. Although there are no known cases of Cliff x Cave hybridization, an extralimital Cave Swallow paired and attended a nest with a Cliff Swallow in Tucson, AZ, in 1984 (Huels 1985); it is unknown whether the offspring produced were hybrids. Hybrid Cliff x Barn swallows have been reported from Pennsylvania (Trotter 1878), New York (Wood et al. 2011), Louisiana (Dittmann and Cardiff 2002), sw. Texas (Mearns 1902), Nebraska (Brown and Page 2015), California (Rogers and Jaramillo 2002) and e. Washington (P. Stoddard pers. comm.), along with internet photos of apparent hybrids from Colorado and Vermont. There is 1 specimen of a hybrid Cliff x Tree (Tachycineta bicolor) swallow (Chapman 1902) from Massachusetts.
Repeated hybridization between Cave and Barn swallows in s. Texas (Martin 1980) was the basis for merging Petrochelidon into Hirundo in 1982 (Am. Ornithol. Union 1982). However, Petrochelidon, a more phylogenetically derived genus than Hirundo (Sheldon and Winkler 1993, Sheldon et al. 2005), represents a distinct group of 7 species of red-rumped, retort-nesting, colonial species distributed worldwide (pyrrhonota, fulva, preussi, rufigula, spilodera, fluvicola, and ariel). Petrochelidon was re-established for the Cliff Swallow in 1997 (Am. Ornithol. Union 1997).
Body size varies clinally, with birds in the north (Alaska and w. Canada) larger than those in the south (s. Arizona and n. Mexico). Wing and tail length vary the most among populations, whereas bill size and tarsus length vary little (Behle 1976). Southern birds have the forehead patch darker (most chestnut, less buff or white). Throat color varies from dark chestnut in the north to pale tawny in the south. Rump patches and underparts tend to be whiter in the north, whereas to the south birds often have the flanks tinged with rust or rufous (Behle 1976).
Subspecies
Four subspecies, following Phillips (1986), diagnosed chiefly on the coloration and pattern of the plumage on the head and on body size. Distinguishing characters listed below are for an adult with unworn plumage.
P. p. pyrrhonota (Vieillot, 1807). Includes Hirundo albifrons Rafinesque, 1822; P. lunifrons (Say, 1823); Hirundo opifex De Witt Clinton, 1824; H. republicana Audubon, 1824; P. p. hypopolia Oberholser, 1920; and P. p. aprilophata Oberholser, 1932 (see Browning 1992). Breeds across n. North America, from n. Alaska east through central Canada to the Maritimes and ne. United States and south; in the West, to nw. Baja California, n. Nevada, and central Colorado; and in the East, from the Ohio Valley, Chesapeake Bay, and (less commonly) to se. United States and the Gulf coast; winters south to central Argentina [type locality = Paraguay]. Throat and cheeks dark chestnut; forehead pale buff or whitish; rump chestnut; large (wing chord > 105 mm).
P. p. ganieri Phillips, 1986 (see Browning 1990). Breeds west of the Appalachians from (probably) s. Oklahoma south through central Texas to s. Texas and east to w.-central Tennessee [type locality = Kerr Co., Texas]; winter range unknown. Like P. p. pyrrhonota, but forehead darker buff; averages smaller (wing chord 102–108 mm; Phillips 1986).
P. p. tachina Oberholser, 1903. Breeds from central California east through s. Nevada to sw. Utah and south through the Lower Colorado River valley to ne. Baja California and east through central Arizona and New Mexico to sw. Texas [type locality = Langtry, Val Verde Co., Texas]; apparently winters south to n. Argentina (Phillips 1986). Similar to P. p. pyrrhonota, but throat and cheeks paler, forehead brownish buff, and chestnut rump darker; averages markedly smaller overall (wing chord < 108 mm).
P. p. melanogaster (Swainson, 1827). Includes Hirundo coronata Lichtenstein, 1831; P. p. swainsoni Sclater, 1858; and P. p. minima van Rossem and Hachisuka, 1938. Breeds from extreme se. Arizona and sw. New Mexico south over the Mexican plateau to Oaxaca and the Pacific plains to Nayarit [type locality = central Mexican Plateau]. Similar to P. p. tachina, but forehead dark chestnut. The ranges of tachina and melanogaster overlap in parts of se. Arizona, and both were found in the same colony near Fairbank, AZ (Jeter 1959).
Related Species
Monophyly of the Hirundinidae, the swallows and martins, has never been questioned, but relationships within the subfamily Hirundininae—a subfamily that includes all but the two species of river martins (Pseudochelidoninae)—have been difficult to tease apart. On the basis of behavior and basic morphology (i.e., ignoring sexually selected traits such as elongated rectrices), the genus Hirundo formerly included a large group of swallows that generally are blue dorsally, white and rufescent ventrally, and build their nests out of mud (Turner and Rose 1989). This treatment changed with the advent of molecular phylogenetics, such that Hirundo was split into three core genera: Hirundo sensu stricto (which includes the familiar Barn Swallow, H. rustica), Cecropis (the striated or red-rumped swallows), and Petrochelidon (the cliff swallows), although this taxonomic split had been recognized earlier by some authorities (e.g., Ridgway 1904, Peters 1960). The genera Delichon (the house martins) and Ptyonoprogne (the crag martins) round out this mud-nester clade (Sheldon et al. 2005). Despite Petrochelidon and Cecropis being lumped with Hirundo in various earlier works, it is actually Ptyonoprogne that is sister to Hirundo, whereas Petrochelidon and Cecropis are sister to each other and together are closest to Delichon (Sheldon et al. 2005).
The nearest living relative in North America of P. pyrrhonota is P. fulva, the Cave Swallow (Sheldon et al. 2005). Formerly little breeding sympatry, but these species have come into contact in Texas as bridges and highway culverts have been constructed. Although there are no known cases of Cliff x Cave hybridization, an extralimital Cave Swallow paired and attended a nest with a Cliff Swallow in Tucson, AZ, in 1984 (Huels 1985); it is unknown whether the offspring produced were hybrids. Hybrid Cliff x Barn swallows have been reported from Pennsylvania (Trotter 1878), New York (Wood et al. 2011), Louisiana (Dittmann and Cardiff 2002), sw. Texas (Mearns 1902), Nebraska (Brown and Page 2015), California (Rogers and Jaramillo 2002) and e. Washington (P. Stoddard pers. comm.), along with internet photos of apparent hybrids from Colorado and Vermont. There is 1 specimen of a hybrid Cliff x Tree (Tachycineta bicolor) swallow (Chapman 1902) from Massachusetts.
Repeated hybridization between Cave and Barn swallows in s. Texas (Martin 1980) was the basis for merging Petrochelidon into Hirundo in 1982 (Am. Ornithol. Union 1982). However, Petrochelidon, a more phylogenetically derived genus than Hirundo (Sheldon and Winkler 1993, Sheldon et al. 2005), represents a distinct group of 7 species of red-rumped, retort-nesting, colonial species distributed worldwide (pyrrhonota, fulva, preussi, rufigula, spilodera, fluvicola, and ariel). Petrochelidon was re-established for the Cliff Swallow in 1997 (Am. Ornithol. Union 1997).