Physical characteristics

True rollers constitute a fairly homogeneous assemblage of medium-sized, heavy-bodied birds characterized by a proportionately large head, short neck, and stout robust bill. Syn-dactylous feet are proportionately small but strong. Broad, long wings reflect strong powers of flight. The rather broad tail may be squarish, slightly rounded, or somewhat forked, sometimes with markedly elongated outermost feathers. Variation in size is not great, and ranges from 10 in (26 cm) and 3 oz (90 g) for the blue-throated roller (Eurystomus gularis), to 14.5 in (37 cm) and 5.3 oz (150 g) for the blue-bellied roller (Coracias cyanogaster). All species are handsomely plumaged in tones of blue or lilac, with olive, chestnut, or pink markings; young birds resemble adults. Modifications in bill structure that evolved in response to different foraging techniques are the key distinguishing feature separating the two genera.

In Coracias, the shrike-like bill is strong, arched, and hook-tipped, and is suited to grasping prey captured on the ground. Eurystomus species catch flying insects, and the short, wide bill is well adapted to aerial feeding.

Ground-rollers are medium-sized terrestrial birds resembling Coracias rollers, but readily distinguished by long legs, distinctive plumage patterns, and short, rounded wings. All are stout-bodied, with a proportionately large head and a strong, robust bill. The large eyes possibly enable these birds to forage effectively in heavily shaded undergrowth, at dusk, or even during the night. Total length for four species with broad, rounded tails is 8.7-13 in (22-33 cm); a very long, graduated tail gives the long-tailed ground roller (Uratelornis chi-maera) a disproportionate total length of 18 in (46 cm). Bold markings are a feature of the rich plumage coloration, with rufous or dark-green upperparts contrasting with finely patterned underparts and striking facial patterns. Sexes are alike, and young birds resemble adults.

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