ThefamilyThreskiornithidae includes 36 species of large wading birds. The family has been traditionally classified into two subfamilies, theibises and thespoonbills; however, recent genetic studies have cast doubt on this arrangement, and have found the spoonbills to be nested within the Old World ibises, and the New World ibises as an early offshoot.
The family Threskiornithidae was formerly known as Plataleidae. The spoonbills and ibises were once thought to be related to other groups of long-legged wading birds in the orderCiconiiformes. A recent study found that they are members of the orderPelecaniformes.[4] In response to these findings, theInternational Ornithological Congress (IOC) recently[when?] reclassified Threskiornithidae and their sister taxaArdeidae under the orderPelecaniformes instead of the previous order of Ciconiiformes.[5] Whether the two subfamilies are reciprocallymonophyletic is an open question. The South American Checklist Committee's entry for the Threskiornithidae includes the following comment "Two subfamilies are traditionally (e.g., Matheu & del Hoyo 1992) recognized: Threskiornithinae for ibises and Plataleinae for spoonbills; because the main distinction has to do with bill shape, additional information, especially genetic, is required to recognize a major, deep split in the family."[6]
A study ofmitochondrial DNA of the spoonbills plus thesacred andscarlet ibises found that the spoonbills formed a clade with old world genusThreskiornis, withNipponia nippon andEudocimus as progressively earlier offshoots and more distant relatives, and hence casts doubt on the arrangement of the family into ibis and spoonbill subfamilies.[7] Subsequent studies have supported these findings, the spoonbills forming a monophyletic clade within the "widespread" clade of ibises, includingPlegadis andThreskiornis, while the "new World Endemic" clade is formed by the genera restricted to the Americas such asEudocimus andTheristicus.[8]
Ibises are a rather old group, with well-preserved definitive fossils known as far back as theEocene (Rhynchaeites), and potential members dating as far back as theLate Paleocene (Dakotornis).[9]
Members of the family have long, broad wings with 11 primaryfeathers and about 20 secondaries. They are strong fliers and, rather surprisingly, given their size and weight, very capable soarers. The body tends to be elongated, the neck more so, with rather long legs. The bill is also long, decurved in the case of theibises, straight and distinctively flattened in thespoonbills. They are large birds, but mid-sized by the standards of their order, ranging from thedwarf olive ibis (Bostrychia bocagei), at 45 cm (18 in) and 450 g (0.99 lb), to thegiant ibis (Thaumatibis gigantea), at 100 cm (39 in) and 4.2 kg (9.3 lb).
They are distributed almost worldwide, being found near almost any area of standing or slow-flowing fresh orbrackish water. Ibises are also found in drier areas, includinglandfills.
TheLlanos are notable in that these wetland plains support seven species of ibis in the one region.[10]
All ibises are diurnal; spending the day feeding on a wide range ofinvertebrates and smallvertebrates: ibises by probing in soft earth or mud, spoonbills by swinging the bill from side to side in shallow water. At night, they roost in trees near water. They are gregarious, feeding, roosting, and flying together, often in formation.
Nesting is colonial in ibises, more often in small groups or singly in spoonbills, nearly always in trees overhanging water, but sometimes on islands or small islands in swamps. Generally, the female builds a large structure out ofreeds and sticks brought by the male. Typical clutch size is two to five; hatching is asynchronic. Both sexes incubate in shifts, and after hatching feed the young by partial regurgitation. Two or three weeks after hatching, the young no longer need to be brooded continuously and may leave the nest, often forming creches but returning to be fed by the parents.
^Hackett, Shannon J.; Kimball, Rebecca T.; Reddy, Sushma; Bowie, Rauri C. K.; Braun, Edward L.; Braun, Michael J.; Chojnowski, Jena L.; Cox, W. Andrew; Han, Kin-Lan; Harshman, John; Huddleston, Christopher J.; Marks, Ben D.; Miglia, Kathleen J.; Moore, William S.;Sheldon, Frederick H.; Steadman, David W.; Witt, Christopher C.; Yuri, Tamaki (June 2008). "A Phylogenomic Study of Birds Reveals Their Evolutionary History".Science.320 (5884):1763–1768.Bibcode:2008Sci...320.1763H.doi:10.1126/science.1157704.PMID18583609.S2CID6472805.
^"Gill, F. & D. Donsker (Eds). 2010. IOC World Bird Names (version 2.4). Available athttp://www.worldbirdnames.org/ [Accessed 29 May 2010].
^Chesser, R.Terry; Yeung, Carol K.L.; Yao, Cheng-Te; Tians, Xiu-Hua; Li Shou-Hsien (2010). "Molecular phylogeny of the spoonbills (Aves: Threskiornithidae) based on mitochondrial DNA".Zootaxa.2603 (2603):53–60.doi:10.11646/zootaxa.2603.1.2.ISSN1175-5326.
^J.L. Ramirez; C.Y. Miyaki & S.N. Del Lama (2013). "Molecular phylogeny of Threskiornithidae (Aves: Pelecaniformes) based on nuclear and mitochondrial DNA".Genetics and Molecular Research.12 (3):2740–2750.doi:10.4238/2013.July.30.11 (inactive 1 July 2025).PMID23979898.{{cite journal}}: CS1 maint: DOI inactive as of July 2025 (link)
^Frederick, Peter C.; Bildstein, Keith L. "Foraging Ecology of Seven Species of Neotropical Ibises (Threskiornithidae) during the Dry Season in the Llanos of Venezuela".The Wilson Bulletin.104 (1):1–21.
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