Coraciidae () is a family of Old World birds, which are known as rollers because of the aerial acrobatics some of these birds perform during courtship or territorial flights. The family contains 13 species and is divided into two genera. Rollers resemble crows in size and build, and share the colourful appearance of kingfishers and bee-eaters, blues and pinkish or cinnamon browns predominating. The two inner front toes are connected, but not the outer one.
They are mainly insect eaters, with Eurystomus species taking their prey on the wing, and those of the genus Coracias diving from a perch to catch food items from on the ground, like giant shrikes.
Although living rollers are birds of warm climates in the Old World, fossil records show that rollers were present in North America during the Eocene. They are monogamous and nest in an unlined hole in a tree or in masonry, and lay 2–4 eggs in the tropics, 3–6 at higher latitudes. The eggs, which are white, hatch after 17–20 days, and the young remain in the nest for approximately another 30 days.
Taxonomy and systematics
The roller family Coraciidae was introduced (as Coracinia) by the French polymath Constantine Samuel Rafinesque in 1815.
It is one of six families in the order Coraciiformes, which also includes the motmots, bee-eaters, todies, ground rollers, and kingfishers. The family gets its scientific name for Latin ', "like a raven", and the English name "roller" from the aerial acrobatics some of these birds perform during courtship or territorial flights.
The phylogenetic relationship between the six families that make up the order Coraciiformes is shown in the cladogram below. The number of species in each family is taken from the list maintained by Frank Gill, Pamela C. Rasmussen and David Donsker on behalf of the International Ornithological Committee (IOC).
A molecular phylogenetic 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).
Genera
The roller family has two extant genera as follows:
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! Image !! Genus !! Living species
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|175px||Coracias ||
- Purple roller (Coracias naevius)
- Indian roller (Coracias benghalensis)
- Indochinese roller (Coracias affinis)
- Purple-winged roller (Coracias temminckii)
- Racket-tailed roller (Coracias spatulatus)
- Lilac-breasted roller (Coracias caudatus)
- Abyssinian roller (Coracias abyssinicus)
- European roller (Coracias garrulus)
- Blue-bellied roller (Coracias cyanogaster)
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|175px||Eurystomus ||
- Blue-throated roller (Eurystomus gularis)
- Broad-billed roller (Eurystomus glaucurus)
- Oriental dollarbird (Eurystomus orientalis)
- Azure dollarbird (Eurystomus azureus)
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Description
Rollers can be identified as medium-sized birds with strong, slightly hooked beaks and stocky bodies, often with brightly colored plumage. Rollers resemble crows in size and build, ranging from in length. They share the colourful appearance of kingfishers and bee-eaters, blues and pinkish or cinnamon browns predominating. Their calls are "repeated short, gruff caws".
Distribution and habitat
The rollers are found in warmer parts of the Old World. Africa has most species, and is believed to be where the family originated. This is supported by the fact that the related ground rollers are found on Madagascar. The European roller is completely migratory, breeding in Europe and wintering in Africa, and the dollarbird also leaves much of its breeding range in winter. Other species are sedentary or short-range migrants.
These are birds of open habitats with trees or other elevated perches from which to hunt.
Behavior
Breeding
Rollers are noisy and aggressive when defending their nesting territories, which they patrol while displaying their striking plumage. Intruders are attacked with intimidating rolling dives. They are monogamous and nest in an unlined hole in a tree or in masonry, and lay 2–4 eggs in the tropics, 3–6 at higher latitudes. The eggs, which are white, hatch after 17–20 days, and the young remain in the nest for approximately another 30 days.