The order Pelecaniformes contains several medium to large waterbirds. Currently, it includes the following families: Pelicans (Pelecanidae), Ibises and Spoonbills (Threskiornithidae), Herons, Egrets and Bitterns (Ardeidae), the Shoebill (Balaenicipitidae), and the Hamerkop (Scopidae).
Great Blue Heron (A. herodias) and Great White Heron (A. herodias occidentalis) meet in a contact zone in Florida where there are mixed breeding pairs, resulting in low levels of gene flow (McGuire et al., 2019).
In Japan, the intergeneric hybridization event between a male Little Egret (E. garzetta) and a female Chinese Pond Heron (Ardeola bacchus) was recorded and described (Mashiko et al., 2012).
In South Dakota, the interbreeding of a Tricolored Heron (E. tricolor) and a Snowy Egret (E. thula) was reported (Meeks et al., 1996). More reports on hybrid herons can be found in the references of these papers, for instance Sprunt (1954).
Several sightings of dark morphs of Little Egret in India might actually be hybrids with Indian Reef Heron (E. schistacea)(Koparde & Yesou, 2017).
A study that set out to investigate whether the Mauritanian Spoonbill (Platalea leucordia balsaci) is a valid subspecies detected introgression from another subspecies, the Eurasian Spoonbill (P. l. leucordia), into P. l. balsaci (Piersma et al., 2012).
Interspecific hybridization of spoonbills has been observed in captivity and nature. The international Zoo Yearbook of 1984, for instance, reports hybridization between a Roseate (Platalea ajaja) and a Eurasian (P. leucorodia) Spoonbill and between an African (P. alba) and a Eurasian Spoonbill.
In South Korea, researchers observed natural hybridization between Black-faced Spoonbill (P. minor) and Eurasian Spoonbill (Kwon et al., 2017).
The Glossy Ibis (P. falcinellus) colonized North America in the 1800s. There, it hybridized with the native White-faced Ibis (P. chihi). Several cases have been documented (Arterburn & Grzybowski, 2003; Faulkner, 2005; Leukering, 2008). Hybridization has resulted in introgression: genes were primarily flowing from White-faced into Glossy Ibis. Moreover, this study uncovered introgression between White-faced Ibis and Puna Ibis (P. ridwayi), a South American species (Oswald et al., 2019).
In the state of New South Wales, Callaghan et al. (2017) observed a possible hybrid between Australian White Ibis (Threskiornis moluccus) and Straw-necked Ibis (T. spinicollis). The plumage of this bird showed characteristics of both putative parental species. It is not the first time that this particular hybrid has been reported. In 1983, Disher described a similar bird, although he also considered the possibility that it was a bird with aberrant plumage. So, to be absolutely sure about the identity of this peculiar bird DNA analysis is probably necessary.
Arterburn, J.W. & Grzybowski,J.A. (2003). Hybridization between Glossy and White-faced ibises. North American Birds 57, 136-139.
Callaghan C., Ryall S. & Kingsford R. (2017) A probable Australian White Ibis Threskiornis moluccus× Straw-necked Ibis T. spinicollis hybrid. Australian Field Ornithology 34, 47-48.
Disher, P. (1983). An unusual ibis. Bird Observer 620, 77.
Faulkner, D. (2005) Hybridization and nesting of Glossy Ibis (Plegadis falcinellus) in Wyoming. North American Birds 59, 382-384.
Koparde, P & Yesou, P (2017) Probable hybrids Little Egret x Indian Reef Heron in India and Sri Lanka. Dutch Birding 39, 238-246.
Kwon, I.-K., Lee, K.-S., Lee, J.-Y., Park, J.-H. & Yoo, J.-C. (2017). Hybridization between the Black-Faced Spoonbill (Platalea minor) and Eurasian Spoonbill (Platalea leucorodia) in South Korea. Waterbirds 40, 77-81.
Leukering, T. (2008) Glossy Ibis and the identification challenges of hybrid Plegadis in Colorado. Colorado Birds 42, 147-149.
Mashiko, M., Fujioka, M., Moriya, K., Hagimoto, T., Yamaguchi, M. & Toquenaga, Y. (2012). Natural Hybridization between a Little Egret (Egretta garzetta) and a Chinese Pond Heron (Ardeola bacchus) in Japan. Waterbirds 35, 160-163.
McGuire, H.L., Taylor, S.S. & Sheldon, F.H. (2019) Evaluating the taxonomic status of the Great White Heron (Ardea herodias occidentalis) using morphological, behavioral and genetic evidence. The Auk 136(1),uky010.
Meeks, W. A., Naugle, D. E., Johnson, R. R. & Higgins, K. F. (1996). Interbreeding of a tricolored heron and a Snowy Egret in South Dakota. Auk 113, 955-957.
Oswald, J.A., Harvey, M.G., Remsen, R.C., Foxworth, D.U., Dittmann, D.L. Cardiff, S.W. & Brumfield, R.T. (2019) Evolutionary dynamics of hybridization and introgression following the recent colonization of Glossy Ibis (Aves: Plegadis falcinellus) into the New World. Molecular Ecology
Piersma, T., van der Velde, M., El-Hacen, E. M., Lok, T. & Overdijk, O. (2012). Molecular verification of the subspecies status of the Mauritanian Spoonbill Platalea leucorodia balsaci. Ardea 100, 131-136.
Sprunt, A. (1954). A hybrid between the Little Blue Heron and the Snowy Egret. The Auk, 314-314.