Great Blue Heron Ardea herodias
Version: 1.0 — Published March 4, 2020
Text last updated April 28, 2011
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Editor's Note: This article requires further editing work to merge existing content into the appropriate Subspecies sections. Please bear with us while this update takes place.
Variation in this species is complex, with general west-east clines from large to small and from dark to pale, although the smallest birds are in the Great Basin (Dickerman 2004a), the largest in the Southeast (Dickerman 1992). In opposition to Bergmann's rule-the ecogeographic principle that ectotherms increase in size at higher latitudes-birds across much of Canada and in the n. Great Plains and Northeast average smaller than birds of the Pacific Coast and Southeast. Conversely, along the Pacific Coast size follows Bergmann's rule (Dickerman 2004b). Payne (1979) asserted that size variation in the East was clinal, but Dickerman (2004a) countered that data are not sufficient to support such an assertion. Birds in the w. West Indies and adjacent continental areas are white (the Great White Heron).
Subspecific variation is contentious, given Oberholser's (1912) recognition of ten subspecies and both Palmer's (1962) and Hancock and Elliot's (1978) support for at least seven subspecies. Yet Payne (1979) recognized just four subspecies, although he provided few data to support his treatment. Dickerman's (2004) comprehensive revision concluded there were four subspecies in North America; his conclusions are followed herein. He did not consider A. h. cognata, but it is recognized here tentatively. That subspecies is said to differ from A. h. wardi slightly in bill and wing measurements (Oberholser 1912), but it may not be diagnosably distinct; more data are needed. The taxon A. wurdemannii Baird, 1858, generally is considered to be a hybrid between A. h. wardi and A. h. occidentalis (Oberholser 1912, Mayr 1956). In diagnosing subspecies, note that plumage color of adults does not differ between the sexes but that females average smaller (Oberholser 1912:533), by about 5% (data from Dickerman 2004a,b). Measurements given below are for the male.
A. h. fannini Chapman, 1901. Resident from sw. Alaska (Prince William Sound) south to the Queen Charlotte Is. [type locality = Skidegate, Queen Charlotte Is.]. Birds resident in sw. British Columbia, including on Vancouver I., and w. Washington are intermediate toward A. h. wardi in color and size (Dickerman 2004a,b), but the status of those on mainland British Columbia north of Vancouver is unclear. Adult dark gray; relative to populations of A. h. wardi on the southern Pacific coast, the culmen (< 134 mm) and tarsi (< 161 mm) are short (Dickerman 2004b), but wing and tail lengths are similar (see mensural data in Oberholser 1912, Dickerman 2004a).
A. h. herodias Linnaeus, 1758. Includes A. h. lessoni Wagler, 1831; A. h. adoxa Oberholser, 1912; and A. h. oligista Oberholser, 1912. Breeds from s.-central British Columbia (east of the Cascades) and e. Washington east to the Maritime Provinces and south to the Dakotas, Indiana, and the Carolinas [type locality = Hudson Bay]; winters south through Middle America to the Caribbean coast of South America and the Greater Antilles (Dickerman 2004a); vagrants have reached Greenland and California (Dickerman 2004a), and birds in the Azores and Britain (e.g., British Ornithologists' Union's Records Committee, Ibis 151:224-230) likely were this subspecies. Adult moderately gray overall; sides of neck vinaceous-gray; chestnut on foreneck dark and extensive, reaching the lower auricular; relative to A. h. fannini, the culmen (> 132 mm) and tarsi (> 163 mm) are long (Dickerman 2004b).
A. h. wardi Ridgway, 1882. Includes A. h. treganzai Court, 1908; A. h. hyperonca Oberholser, 1912; and A. h. sanctilucae Thayer and Bangs, 1912. Largely resident in the s. United States, from s. Washington east to through Nebraska to South Carolina south through the Baja California peninsula, coastal nw. Mexico, ne. Tamaulipas, and n. Florida [type locality = Estero Bay, Florida, per Holt 1925]; winters south to at least n. Central America (Dickerman 2007). Adult pale gray overall; sides of neck pinkish-gray; chestnut on foreneck pale and reduced, not reaching auricular; bill depth generally < 30 mm (Oberholser 1912).
A. h. occidentalis Audubon, 1835, the Great White Heron. Includes A. h. repens Bangs and Zappey, 1905. Resident in s. Florida, Cuba, Jamaica, and n. Yucatan Peninsula [type locality = Key West, Florida]; vagrants have occurred west to Texas and north to Nova Scotia (Mitra and Fritz 2002). Size of A. h. wardi of the Southeast (McGuire 2002) but adult plumage all white; relative to A. h. wardi, plumes on the breeding adult are reduced or absent (Holt 1928) and the bill averages longer (Mayr 1956).
A. h. cognata Linnaeus, 1758. Resident on the Galapagos Is. [type locality = Santa Cruz, Indefatigable I.]. Like A. h. wardi but bill deeper (≥ 29 mm; Oberholser 1912).
Great Blue Heron (Blue form) Ardea herodias [herodias Group]
Ardea herodias fannini
Ardea herodias herodias
Ardea herodias wardi
Ardea herodias cognata
Great Blue Heron (White form) Ardea herodias occidentalis
Herons of the genus Ardea, which are distributed worldwide (except on Antarctica) form a clade with other "typical" herons, including egrets of the genus Egretta, night-herons (tribe Nycticoracini), the green herons (genus Butorides), and the Whistling Heron (Syrigma sibilatrix), a Neotropical species (Sheldon et al. 2000, Chang et al. 2003). Ardea is an old genus; early fossils resemble A. alba, the Great Egret (Becker 1986).
Three widespread Ardea species, A. herodias of North America, A. cinerea of Eurasia and Africa, and A. cocoi of South America, form a superspecies (Bock 1956, Palmer 1962, Hancock and Elliot 1978, Payne 1979, Sibley and Monroe 1990). These species resemble one another phenotypically (Bock 1956), behaviorally (Curry-Lindahl 1971), and genetically (Sheldon 1987).
The Great White Heron (A. h. occidentalis) has been treated as a species (e.g., Holt 1928, Palmer 1962) or as a color morph-i.e., not a taxon at all (but see Mayr 1956). Its behavior may (Curry-Lindahl 1971) or may not differ from that of A. h. wardi (Meyerriecks 1957). "Wurdemann's Heron" generally is considered to be a hybrid swarm of A. h. wardi and A. h. occidentalis, and A. h. wardi and A. h. occidentalis do interbreed where ranges meet in the Florida Keys (Meyerriecks 1957). That said, Stevenson and Anderson (1994:59) stated that a nest of two Wurdemann's Herons was unknown and therefore concluded that hybrids were inviable, suggesting reproductive isolation.
More recently, McGuire (2002) found that Wurdemann's Heron is fertile and does form breeding pairs. On the basis of her extensive observations of mated pairs, McGuire (2002) concluded that pairing between blue and white birds could not be considered random; nonetheless, hybrid pairs were common enough to prevent genetic divergence at mitochondrial loci, although microsatellite markers differed in frequency (McGuire 2002). Still, most genetic differences separated birds from Florida Bay and the Keys from birds on the Florida Peninsula.
Large herons referable to the living genus Ardea have been in existence since the middle Miocene and probably before, although the phylogenetic relationships of fossil species to living species is still not clear.
Earliest record for Ardea is an undescribed species from the early Barstovian North American Land Mammal Age (NALMA: 14 million yr before present) from Observation Quarry, Dawes Co., NB, about the size of the Great Egret (Casmerodias albus; Becker 1986a). Next record for Ardea sp. from the late Clarendonian NALMA (10 mybp) from Love Bone Bed, Alachua Co., FL, the size of A. h. occidentalis (Becker 1986a). Ardea polkensis Brodkorb (Brodkorb 1955:17), the only correctly named fossil species within the geographic range of the living species (Olson 1985d: 165–168), from the late Hemphillian NALMA (5 mybp; Bone Valley, Polk Co., FL); was smaller than A. herodias . A late Blancan NALMA (2 mybp) Ardea sp. record, recently made by Emslie (Emslie 1992) from the Macasphalt Shell Pit, Sarasota Co., FL, was slightly smaller than female herodias and equal in size to the White-necked Heron, A. cocoi .
Fossils of A. herodias recorded from many Pleistocene (1.8 mybp) and prehistoric sites within the U.S. (see Becker Becker 1982: 449, Becker 1984: 203, Becker 1985b: 38, also Brodkorb 1963a: 284, Guthrie 1992: 321, Parmelee Parmalee 1977: 200, 1985: 176, Howard 1969), Mexico (Hamblin and Rea 1985), and St. Croix in the West Indies (Wetmore 1937).