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THRESKIORNITHIDAE - IBISES AND SPOONBILLS
Six species arranged into two subfamilies (see below) with the most obvious difference being bill morphology and resultant feeding method. It is likely that the current classification does not fully represent the complexity of taxonomic relationships in the family. Members of this family have a long neck and robust body. The bill is long and slit-like nostrils are located laterally and basally to allow breathing whilst feeding. A groove along the mandible acts as a canal for diverting secretions from the supraorbital salt gland. Feeding methods are tactile, through the eyes are slightly forward-facing giving binocular vision. Schizorhinal cranial morphology is an adaptation allowing free movement of the upper mandible for tactile feeding. All species show some bare skin on the head, though it is variable in extent, restricted to the chin and lores in Theristicus, whilst Platalea is wholly "bald". Legs are long and sturdy with the lower half of the tibia bare. The toes are of moderate length and the hallux is slightly raised. The three forward-facing toes are linked with a small basal membrane. The claw of the middle toe is "cupped" and is used for feather maintenance. Flight is powerful and fast, in formation in gregarious species, and involves flapping interspersed with periods of gliding. Flocks synchronise their movements so that all flap and all glide at the same time. The neck and legs are outstretched in flight, though they do not extend beyond the tail in all species. The wings are long and broad, with 11 primaries (11th much reduced) and 20 secondaries. The tail is short and consists of 12 retrices. Down is present on all feather tracts and there are areas of apteria (unfeathered skin). There is a partial pre-breeding moult and a complete post-breeding moult. Breeding is monogamous and colonial, sometimes in association with other waterbirds. South America appears to be a centre of radiation for the family.
Threskiornithinae "Ibises" (Mesembrinibis, Phimosus, Plegadis and Theristicus) Bill long, thin and downcurved used for probing soil.
Plataleinae "Spoonbills" (Platalea) Bill broadened and flattened distally in typical "spoon" shape, used for head-sweeping feeding motion in aquatic habitats.
REFERENCES
Campbell B & Lack E 1985 - A Dictionary of Birds - T & AD Poyser.
Elliott A 1992 - Ciconiidae Handbook of the Birds of the World Volume 1 - Lynx Ediciones.
Hancock JA, Kushlan JA & Kahl MP 1992 - Storks, Ibises and Spoonbills of the World - Academic Press.
