Coraciidae Rollers
Version: 1.0 — Published March 4, 2020
Introduction
Stocky birds with large heads, broad shoulders, and stout bills, rollers are united by their method of sit-and-wait predation on large insects, other invertebrates, or even reptiles and rodents. Rollers are named for their acrobatic display flights, in which they dive rapidly toward the ground with wings and body rolling back and forth. Many are a distinctive light blue color overall with darker patches of intense pure blue, though many have a good deal of brown in their plumage. Dollarbirds, named for the shiny white coin-sized patch on each wing, are stockier and darker in color than the other rollers. All are hole-nesters, with white, nearly spherical eggs much like those of many other coraciiform birds.
Habitat
Most rollers live in open habitats, often with some trees, including woodland, savanna, and even the edges of dense tropical forest.
Diet and Foraging
Rollers are carnivorous, feeding on animals ranging from small insects to small vertebrates. Coracias species are sit-and-wait predators that generally pounce on prey on the ground. Eurystomus species are more frequently aerial insectivores, sallying from a perch after flying insect prey.
Breeding
Coraciids are monogamous with biparental care. Most species do not construct their own nests, but instead use natural tree cavities, rock crevices, or holes previously excavated by other birds. The nest cavity is lined at most with a thin pad of vegetation, but is more often bare. Females lay 2 to 4 eggs in the tropics, and up to 6 in the temperate zone. Only the female incubates at night, but otherwise both sexes take near-equal roles in parental care. After 17 to 24 days of incubation, the chicks hatch naked, asynchronously, but by fledging, 25 to 30 days later, all the nestlings can leave the nest within a day or two of each other. They are fed for at least a few days more, though this, like all other details of their breeding biology, is not well known.
Conservation Status
Two coraciid species (15%) have conservation concerns (2 NT). The European Roller Coracias garrulus, widespread in Europe and the Middle East, is declining rapidly, apparently as traditional pasture is being replaced by intensive agriculture; the Azure Dollarbird Eurystomus azureus, an endemic to the island of Sulawesi, has declined rapidly with the logging of that island’s forests.
Systematics History
Recent morphological and genetic evidence supports a sister relationship between Coraciidae and Brachypteraciidae (Cracraft 1971, 1981, Kirchman et al. 2001, Ericson et al. 2006a, Hackett et al. 2008, Mayr 2011). The clade formed of these two families is in turn closely related to the group comprising Alcedinidae, Todidae, and Momotidae (Kirchman et al. 2001, Livezey & Zusi 2001, Ericson et al. 2006a, Hackett et al. 2008).
Conservation Status
Least Concern |
92.3%
|
---|---|
Near Threatened |
7.7%
|
Vulnerable |
0%
|
Endangered |
0%
|
Critically Endangered |
0%
|
Extinct in the Wild |
0%
|
Extinct |
0%
|
Not Evaluated |
0%
|
Data Deficient |
0%
|
Unknown |
0%
|
Data provided by IUCN (2023) Red List. More information