Crimson sunbirds are tiny, only 11 cm long. They have medium-length thin down-curved
bills and brush-tipped tubular tongues, both adaptations to their nectar feeding. The adult male has a crimson breast and maroon back, with black malar stripes. The rump is yellow and the belly is olive. The female has an olive-green back, yellowish breast and white tips to the outer tail
feathers. In most of the range, males have a long green-blue tail, but
A.s. nicobarica of the
Nicobar Islands and the former subspecies
A. vigorsii (
Western crimson sunbird) of the Western Ghats of India lack the long central tail feathers. Their
call is
chee-cheewee. Crimson sunbird (Aethopyga siparaja) male Bach Ma.jpg|typical side view of male Crimson sunbird (Aethopyga siparaja) male Bach Ma 2.jpg|showing irridescent cap and 'moustache' Crimson Sunbird feeding.jpg|male Feeding on Hibiscus sp. ==Distribution and habitats==