Threskiornithidae
Family of birds
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Taxonomy
The spoonbills and ibises were once thought to be related to other groups of long-legged wading birds in the order Ciconiiformes, until genetic studies found that they are members of the order Pelecaniformes. In response to these findings, the International Ornithological Congress (IOC) reclassified Threskiornithidae and their sister taxa Ardeidae under the order Pelecaniformes, instead of the previous order of Ciconiiformes, in 2010.
A study of mitochondrial DNA of the spoonbills plus the sacred and scarlet ibises found that the spoonbills formed a clade with old world genus Threskiornis, with Nipponia nippon and Eudocimus as progressively earlier offshoots and more distant relatives, and hence casts doubt on the arrangement of the family into ibis and spoonbill subfamilies. Subsequent studies have supported these findings, the spoonbills forming a monophyletic clade within the "widespread" clade of ibises, including Plegadis and Threskiornis, while the "new World Endemic" clade is formed by the genera restricted to the Americas such as Eudocimus and Theristicus.
Ibises are a rather old group, with well-preserved definitive fossils known as far back as the Eocene (Rhynchaeites), and potential members dating as far back as the Late Paleocene (Dakotornis).
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Description
Members of the family have long, broad wings with 11 primary feathers 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 the ibises, straight and distinctively flattened in the spoonbills. They are large birds, but mid-sized by the standards of their order, ranging from the São Tomé ibis (Bostrychia bocagei), at 45 cm (18 in) and 450 g (0.99 lb), to the giant ibis (Pseudibis gigantea), at 100 cm (39 in) and 4.2 kg (9.3 lb).
Distribution and ecology
They are distributed in tropical and warm temperate regions almost worldwide, being found near almost any area of standing or slow-flowing fresh or brackish water away from cool temperate and arctic zones. Ibises are also found in drier areas, including using human detritus in landfills by some species, and semi-desert fields by the northern bald ibis. The northernmost occurrence is Eurasian spoonbill, breeding north to 57°N in northern Denmark, and the southernmost is black-faced ibis, south to 55°S in Tierra del Fuego.
The Llanos are notable in that these wetland plains support seven species of ibis in the one region.
Ibises and spoonbills feed on a wide range of invertebrates and small vertebrates; ibises by probing in soft earth or mud, spoonbills by swinging the bill from side to side in shallow water. They roost in trees near water, or standing in shallow water. They are gregarious, feeding, roosting, and flying together, often in formation.
Nesting is colonial in large or small groups or occasionally singly, nearly always in trees overhanging water, but sometimes on islands or small islands in swamps. Generally, the female builds a large structure out of reeds and sticks brought by the male. The 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.
Species
There are 35 extant species of ibis and spoonbill, and one (Réunion ibis) that became extinct in historical times.
Fossil genera
The following fossil genera are known:
- Actiornis (Late Eocene of England)
- Apteribis. Several species of flightless ibises from Hawaii.
- ?Dakotornis (Late Paleocene of North Dakota, US)
- Gerandibis. Discovered in France. It is the sole species known for this genera.
- ?Minggangia (Late Eocene of China)
- Rhynchaeites (Early to Middle Eocene of England and Germany, potentially Denmark and Wyoming, US)
- ?Vadaravis (Early Eocene of Wyoming, US)
- Xenicibis. Discovered in Jamaica.