''Eurystomus'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial n ...

of roller, one of the two genera in that family of

bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

s. The name means ‘broad mouth’, from the Greek ''eurus'' (, ‘broad, wide’) and ''stoma'' (, ‘mouth’). ''Eurystomus'' contains four broad-billed species, which breed in Africa, Asia and Australasia. Two species are restricted to Africa, one of which, the

broad-billed roller The broad-billed roller (''Eurystomus glaucurus'') is a member of the roller family of birds which breeds across tropical Africa and Madagascar in all but the driest regions. It is a wet season breeder, which migrates from the northern and sout ...

, is migratory. The oriental dollarbird has a large distribution ranging from India to Japan and Australia and it too, is migratory over the northern and southern extremes of its range. The final species, the azure dollarbird, is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found els ...

to the

Moluccas The Maluku Islands (; Indonesian: ''Kepulauan Maluku'') or the Moluccas () are an archipelago in the east of Indonesia. Tectonically they are located on the Halmahera Plate within the Molucca Sea Collision Zone. Geographically they are located ...

in Indonesia. In general they are open country foragers, occurring in woodland, savanna and farmland. The azure dollarbird and the broad-billed roller are both associated with rainforests but nevertheless require open areas in which to forage. The species of the genus ''Eurystomus'' vary from the other genus of rollers, ''

Coracias ''Coracias'' is a genus of the rollers, an Old World family of near passerine birds related to the kingfishers and bee-eaters. They share the colourful appearance of those groups, blues and browns predominating. The two outer front toes a ...

'', in having proportionally longer wings and shorter legs. These morphological differences are reflected in differences of foraging techniques. ''Coracias'' rollers forage from a fixed perch and take prey by swooping down onto it on the ground, while the faster and more agile ''Eurystomus'' rollers catch their prey on the wing. Unlike the species of the genus ''Coracias'', they do not perform the "rolling" display which gives the family its common name.

Taxonomy

The genus ''Eurystomus'' was introduced in 1816 by the French ornithologist

Louis Jean Pierre Vieillot Louis Pierre Vieillot (10 May 1748, Yvetot – 24 August 1830, Sotteville-lès-Rouen) was a French ornithologist. Vieillot is the author of the first scientific descriptions and Linnaean names of a number of birds, including species he colle ...

to accommodate the Oriental dollarbird. The name is from

Classical Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic peri ...

''eurustomos'' meaning "wide-mouthed". A

molecular phylogenetic Molecular phylogenetics () is the branch of phylogeny that analyzes genetic, hereditary molecular differences, predominantly in DNA sequences, to gain information on an organism's evolutionary relationships. From these analyses, it is possible to ...

study by Ulf Johansson and collaborators published in 2018 found that the azure dollarbird (''Eurystomus azureus'') was nested in a clade containing subspecies of the Oriental dollarbird (''Eurystomus orientalis'').

Species

References

* ''Kingfishers, Bee-eaters and Rollers'' by Fry, Fry and Harris, Bird genera Taxa named by Louis Jean Pierre Vieillot {{Coraciiformes-stub