Oriental dwarf kingfisher

The oriental dwarf kingfisher is one of the smallest known kingfisher species.[9] It is only slightly larger than a medium-sized hummingbird[9] and measures 12.5–14 cm in length (including bill and tail).[7][9][5] Females typically weigh 14-16g and males 14-21.5g,[5] making the males slightly larger. The two sexes are otherwise alike and sexual dimorphism is not present.[7] 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.[7][5] 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.[5] 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.[7] The toe-count in these kingfisher species does not appear to be adaptive.[7]

Kingfishers (Alcedinidae) are a family of approximately 114 species belonging to the pantropical avian order Coraciiformes.[10] Members of this family range in size from the 9g African dwarf kingfisher (Ceyx lecontei) to the 500g laughing kookaburra (Dacelo novaeguinea).[11] 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.[11] This family is largely tropical, however, there are a few species which have adapted to temperate regions.[11]

This family can be further divided into the three subfamilies: Halcyoninae, Cerylinae, and Alcedinidae[10] (the pygmy kingfishers).[4] The subfamily Alcedinidae is distributed across tropical Africa and Asia, south into northern Australia and Melanesia, and north into Europe and temperate Asia.[4] As implied by their name, pygmy kingfishers are relatively tiny compared to other kingfishers.[4] Other than their size, kingfishers in this subfamily are also characterized by their bright colours.[4] Their habitats range from dense forest to woodland-savannah, and they can also be found along waterways in both wooded and open terrain.[4]

Within the Alcedinidae subfamily is the genus Ceyx.[4] 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.[4] 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.[5][6]

Rufous-backed kingfisher (Ceyx rufidorsa)

Oriental dwarf kingfisher (Ceyx erithaca)

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.[5][12][13] A recent study has revealed genetic differences between C. erithaca and C. rufidorsa, suggesting that they are not morphs, but two distinct lineages.[5][12][13] 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.[5][12][13]

The oriental dwarf kingfisher is a forest and wetland-dwelling species that is endemic across much of the Indian subcontinent and Southeast Asia.[8][7][5] Populations have been found in Bangladesh, Bhutan, Brunei, Cambodia, China, India, Indonesia, Laos, Malaysia, Myanmar, Philippines, Singapore, Sri Lanka and Vietnam.[8][7][5]

It is most commonly found in deciduous and evergreen primary and secondary forests,[7] but also in alluvial forests, mangroves, overgrown rubber gardens, or in dense aggregations of palms, bamboos, or shrubs.[5] They tend to keep near forest streams and ponds,[7] but their nests are often well away from water.[5] They keep low to the ground and are known to perch and fly within 1-2m of the forest floor.[7] Their preferred habitat is densely shaded forest lowlands near small streams or ponds.[7][14] The lowlands they are present in typically do not exceed 1000-1300m in elevation.[8][7]

C. erithaca is classified as a "Least Concern Species" under the IUCN Red List[8] and it is not globally threatened.[5] The population trend, however, is decreasing[8][5] and the number of mature individuals is unknown.[8] It is widely distributed, but in the northern parts of the range, it is often reported as scarce.[5] This scarcity could be due to the species being overlooked, and/or a result of its movement patterns.[5] There are conservation sites identified over the species' entire range.[8]