Black-backed Dwarf-kingfisher

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.

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

Migration

The northern populations winter in the southern parts of the breeding range and the species is defined as a partial migrant. They often migrate south towards peninsular Malaysia from August to September and return north in March. Large numbers of night-flying migrants are reported from August to December at Maxwell's Hill and at Fraser's Hill in Malaysia, as well as at light stations on many islands up to 60 km off the western coast. It is still uncertain whether the most northerly parts of the species' range are vacated during the winter. The oriental dwarf kingfisher is also a breeding visitor across much of the range in India, but its movements here are still uncertain.

Behaviour and ecology

Breeding

Egg laying occurs from July to September in southwest India, February to July in Sri Lanka, April to May in northeast India, March to July in peninsular Malaysia, March in Sumatra, and from December to May in Java. Nests are built in stream banks, road cuttings, terrestrial termitariums, or in soil near roots of a fallen tree, often well away from water. Together, the male and female excavate a horizontal tunnel that is 15–100 cm long, 3.8-4.5 cm in diameter, and ends in an unlined egg chamber. One pair dug 25 cm of their burrow, in sand, in about 40 minutes. The unlined chamber is 10–15 cm wide and 5–7 cm high. Both the tunnel and egg chamber are inclined upwards, which is thought to minimize water entry into the chamber and to help the flow of waste material out of the nest. The generation time is approximately 4.2 years. A typical clutch size is 3-7 eggs, averaging to around 5 eggs per clutch. The eggs are laid in the morning with a one day interval in between. Incubation begins after the final egg is laid and the incubation period lasts 17–18 days. Both the male and female incubate the eggs, however, the female has a larger role in the incubation period because she is responsible for incubating the eggs at night. The fledging period is 18–20 days and chicks typically fledge out in the morning.

Diet

Their diet consists primarily of insects, including mantises (Mantodea), grasshoppers (Orthoptera), flies (Diptera), water beetles (Dytiscidae), winged ants ( Formicidae), mayflies ( Ephemeroptera); but also includes spiders; worms (Oligochaeta); and small crabs, fish, frogs and lizards.

Oriental dwarf kingfishers forage solitarily and perch in low vegetation or on rocks before flying out to capture prey from the ground or from among foliage. They can take spiders from their webs and catch insects in flight. They can also dive into water for prey at or just below the surface, without submerging themselves. Larger prey are typically brought back to a perch, where the bird will strike it repeatedly with its beak before swallowing.

Vocalizations

High pitched, shrill "tsriet-tsriet" or soft "tjie-tjie-tjie" in flight.

Conservation status and threats

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

Threats

The main threat being faced by the oriental dwarf kingfisher is the clearing of their forest habitat. Population levels are likely to decrease due to the continued loss of critical breeding habitats due to human activities.

Oriental dwarf kingfishers may also face other threats common to kingfishers and other migrating bird species, such as:
* Pollution
* Drying of ponds and streams
* Public dislike for kingfishers (fishermen)/illegal human persecution
* Electric lines
* Climate-induced changes in timing of migration and breeding
* Collisions with artificial obstacles, like buildings, in their flight path
* Exhaustion, starvation and dehydration
* Erosion of stream banks

References

{{Taxonbar, from=Q1052008

Oriental dwarf kingfisher
Oriental dwarf kingfisher
Birds of Northeast India
Birds of South India
Birds of Hainan
Birds of Southeast Asia
Oriental dwarf kingfisher
Oriental dwarf kingfisher