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''Eurystomus'' is a
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
roller Roller may refer to: Birds *Roller, a bird of the family Coraciidae * Roller (pigeon), a domesticated breed or variety of pigeon Devices * Roller (agricultural tool), a non-powered tool for flattening ground * Road roller, a vehicle for compa ...
, 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 lightweigh ...
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 south ...
, is migratory. The
oriental dollarbird The Oriental dollarbird (''Eurystomus orientalis'') is a bird of the roller family, so named because of the distinctive pale blue or white, coin-shaped spots on its wings. It can be found from Australia to Korea, Japan and India. Taxonomy The O ...
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 The azure dollarbird (''Eurystomus azureus'') also known as the azure roller, purple dollarbird or purple roller, is a species of bird in the family Coraciidae. It is endemic to the Maluku Islands in Indonesia. Formerly, some authorities consider ...
, 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 elsew ...
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 eas ...
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 are co ...
'', 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 collecte ...
to accommodate the
Oriental dollarbird The Oriental dollarbird (''Eurystomus orientalis'') is a bird of the roller family, so named because of the distinctive pale blue or white, coin-shaped spots on its wings. It can be found from Australia to Korea, Japan and India. Taxonomy The O ...
. 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 The azure dollarbird (''Eurystomus azureus'') also known as the azure roller, purple dollarbird or purple roller, is a species of bird in the family Coraciidae. It is endemic to the Maluku Islands in Indonesia. Formerly, some authorities consider ...
(''Eurystomus azureus'') was nested in a
clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
containing
subspecies In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...
of the
Oriental dollarbird The Oriental dollarbird (''Eurystomus orientalis'') is a bird of the roller family, so named because of the distinctive pale blue or white, coin-shaped spots on its wings. It can be found from Australia to Korea, Japan and India. Taxonomy The O ...
(''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