The oriental dwarf kingfisher (Ceyx erithaca), also known as the black-backed kingfisher or three-toed kingfisher, is a pocket-sized bird in the family Alcedinidae. This tropical kingfisher is a partial migrant that is endemic across much of the Indian Subcontinent and Southeast Asia. It resides in lowland forests, typically near streams or ponds, where it feeds upon insects, spiders, worms, crabs, fish, frogs, and lizards. This small bird is easily distinguishable from other birds in its range due to its red bill, yellow-orange underparts, lilac-rufous upperparts, and blue-black back.
Description
The oriental dwarf kingfisher is one of the smallest known kingfisher species. It is only slightly larger than a medium-sized hummingbird and measures 12.5–14 cm in length (including bill and tail). Females typically weigh 14-16g and males 14-21.5g, making the males slightly larger. The two sexes are otherwise alike and sexual dimorphism is not present. Both males and females have a black spot on the forehead; blue and white patches on the side of the neck; a lilac-rufous crown, rump, and tail; a dark blue back and wings; a white chin and throat; pale yellow-orange underparts; a dark brown iris; and red legs, feet, and bill. Juveniles are duller and have less lilac colouring; a white chin, throat and belly; yellow-orange bill with pale tip; and blue scapulars and wing-coverts. This species of kingfisher has three toes, explaining why it is sometimes called the three-toed kingfisher, however, there are other kingfishers which also have three toes. The toe-count in these kingfisher species does not appear to be adaptive.
Taxonomy and systematics
Kingfishers (Alcedinidae) are a family of approximately 114 species belonging to the pantropical avian order Coraciiformes. Members of this family range in size from the 9g African dwarf kingfisher (Ceyx lecontei) to the 500g laughing kookaburra (Dacelo novaeguinea). Despite their name, members of this family are not all piscivorous and many are found far from water and are predators to terrestrial invertebrates and small vertebrates. This family is largely tropical, however, there are a few species which have adapted to temperate regions.
This family can be further divided into the three subfamilies: Halcyoninae, Cerylinae, and Alcedinidae (the pygmy kingfishers). The subfamily Alcedinidae is distributed across tropical Africa and Asia, south into northern Australia and Melanesia, and north into Europe and temperate Asia. As implied by their name, pygmy kingfishers are relatively tiny compared to other kingfishers. Other than their size, kingfishers in this subfamily are also characterized by their bright colours. Their habitats range from dense forest to woodland-savannah, and they can also be found along waterways in both wooded and open terrain.
Within the Alcedinidae subfamily is the genus Ceyx. Species in this genus are characterized by their terrestrial habitats, their diet which consists mostly of insects, their dorso-ventrally flattened orange bills and their more rufous upperparts. Within this genus, molecular data indicates that C. erithaca forms a well-supported clade of three-toed pygmy kingfishers that includes C. melanurus, C. lepidus, C. argentatus and C. cyanopectus. C. erithaca comprises two principal colour morphs: the black morph, the black-backed kingfisher or oriental dwarf kingfisher, and the rufous morph, which is sometimes designated as a separate species, the rufous kingfisher, C. rufidorsa. A recent study has revealed genetic differences between C. erithaca and C. rufidorsa, suggesting that they are not morphs, but two distinct lineages. The study suggests that the extensive colour polymorphism may have resulted from introgressive hybridization that occurred in the distant past, when the two morphs were diverging from one another.
Habitat and distribution
The oriental dwarf kingfisher is a forest and wetland-dwelling species that is endemic across much of the Indian subcontinent and Southeast Asia. Populations have been found in Bangladesh, Bhutan, Brunei, Cambodia, China, India, Indonesia, Laos, Malaysia, Myanmar, Philippines, Singapore, Sri Lanka and Vietnam.