Scarlet Ibis - Taxonomy

Taxonomy

The species was first classified by Carl Linnaeus in 1758. Initially given the binomial nomenclature of Scolopax rubra (the name incorporates the Latin adjective ruber, "red"), the species was later designated Guara rubra and ultimately Eudocimus ruber.

Biologically the Scarlet Ibis is very closely related to the American White Ibis (Eudocimus albus) and is sometimes considered conspecific with it, leaving modern science divided over their taxonomy. The two birds each have exactly the same bones, claws, beaks, feather arrangements and other features – their one marked difference lies in their pigmentation. Traditional taxonomy has regarded the two as separate and distinct.

Early ornithological field research revealed no natural crossbreeding among the red and white, lending support to the two-species viewpoint. More recent observation, however, has documented significant crossbreeding and hybridisation in the wild. Researchers Cristina Ramo and Benjamin Busto found evidence of interbreeding in a population where the ranges of the Scarlet and White Ibises overlap along the coast and in the Llanos in Colombia and Venezuela. They observed individuals of the two species mating and pairing, as well as hybrid ibises with pale orange plumage, or white plumage with occasional orange feathers, and have proposed that these birds be classified as a single species. Hybridisation has been known to occur frequently in captivity.

Some biologists now wish to pair them with Eudocimus albus as two subspecies of the same American ibis. Others simply define both of them as one and the same species, with ruber being a color variation of albus.