Dicruridae – Drongos

The Dicruridae (Drongos), are a family of passerines of the Old-World tropics. They are related to the Rhipidurinae (Australasian Fantails), Monarchinae (Monarchs and Paradise Flycatchers) and Grallininae (Magpie-larks).

Drongos are mostly black or dark grey, short-legged birds, with an upright stance when perched. They have forked tails and some have elaborate tail decorations. They feed on insects which they catch in flight. Several species of animals and birds respond to drongos’ alarm calls, which often warn of the presence of a predator. They have been shown to utter hoax alarm calls in order to benefit from the false alarms as other birds scatter leaving them to the food source. (Fork-tailed or Common Drongos in the Kalahari Desert are known to use alarm calls in the absence of a predator to cause animals to flee and abandon food, which they eat, getting up to 23% of their food this way.) These insectivorous birds are usually found in open forests or bush. They sit very upright whilst perched, like a shrike. Two to four eggs are laid in a nest high in a tree. Despite their small size, they are aggressive and fearless, and will attack much larger species if their nest or young are threatened.

The Black Drongo Dicrurus macrocercus is typical of the family. It is a common resident breeder in much of tropical southern Asia from southwest Iran through Pakistan, India, Bangladesh and Sri Lanka east to southern China and Indonesia and accidental visitor of Japan. It is an all-black bird with a distinctive forked tail and measures 28 cm in length. It feeds on insects, and is common in open agricultural areas and light forest throughout its range, perching conspicuously on a bare perch or along power or telephone lines.

It is known for its aggressive behaviour towards much larger birds, such as crows, never hesitating to dive-bomb any bird of prey that invades its territory. This behaviour earns it the informal name of ‘king crow’. Smaller birds often nest in the well-guarded vicinity of a nesting Black Drongo. Previously grouped along with the African Fork-tailed Drongo Dicrurus adsimilis, the Asian forms are now treated as a separate species with several distinct populations. It is listed as least concern by the International Union for Conservation of Nature (IUCN) on the IUCN Red List, due to its large range and relative commonness. It has been introduced to some Pacific islands, where it has thrived and become abundant to the point of threatening and causing the extinction of native and endemic bird species there.

Like most drongos, this bird is glossy black with a wide fork to the tail. Adults usually have a small white spot at the base of the gape. The iris is dark brown (not crimson as in the similar Ashy Drongo). The sexes cannot be told apart in the field. Juveniles are brownish and may have some white barring or speckling towards the belly and vent, and can be mistaken for the White-bellied Drongo. First-year birds have white tips to the feathers of the belly, while second-years have these white-tipped feathers restricted to the vent. They fly with strong flaps of the wing and are capable of fast manoeuvres that enable them to capture flying insects. With short legs, they sit upright on thorny bushes, bare perches or electricity wires. They may also perch on grazing animals. They are capable of producing a wide range of calls but a common call is a two note ‘tee-hee’ call resembling that of the Shikra Accipiter badius.

Found predominantly in open country, it usually perches and hunts close to the ground. They are mostly aerial predators of insects, but also glean from the ground or off vegetation. Some populations show seasonal movements that are poorly understood while populations in Korea are known to be migratory. It can be found in savanna, fields, and urban habitats.

They become active very early at dawn and roost later than many other birds. They feed mainly on insects such as grasshoppers, cicadas, termites, wasps, bees, ants, moths, beetles and dragonflies. They sometimes fly close to tree branches, attempting to disturb any insects that may be present. They congregate in fields being ploughed, picking up exposed caterpillars and beetle grubs. As many as 35 birds have been seen at such congregations. They are also attracted to fires in scrub and grasslands habitats where insects are disturbed. They appear to avoid flies. They associate with Common Mynas, Cattle Egrets and other birds that share a similar diet and habitat. Drongos benefit from this association and are more successful in their foraging. There is only partial overlap in the insect prey sought by Mynas and Drongos although in rare instances the drongos may rob prey from mynas.

It has been suggested that they may feed on birds more intensively on migration. An individual on a migratory stop-over island in Korea caught several birds one after the other, killing them by striking at the back of the head and neck and feeding selectively on parts, especially the brain. They have also, on occasion, been seen feeding on fish. Flowers of trees such as Erythrina and Bombax may be visited for water and nectar and they are sometimes known to feed on grains. They are only rarely known to take larger arthropods such as scorpions and centipedes. They feed on milkweed butterflies that are often avoided by other predators and are known to feed late in the evening or night, often on insects attracted to artificial lights.

Black Drongos breed mainly in February and March in southern India, and until August in other parts of the country. Males and females sing in the mornings during the breeding season. Courtship can include aerobatic chases and they may lock their wings and beaks together, with the pair sometimes falling to the ground. Displays may be made on the ground. Pair bonds are retained for a whole breeding season. Their nest is a cup made with a thin layer of sticks placed in the fork of branch, and is built in a week by both the male and female. Eggs are laid close to the first rains in April. The usual clutch is three or rarely four eggs laid in a cup nest placed in the fork of an outer branch of tree. Large leafy trees such as the jackfruit are preferred. The eggs are pale cream to red with spots and markings and are 26 mm long and 19 mm wide. The eggs are incubated by both parents and hatch after 14 to 15 days. Nestlings are brooded for the first five days, after which the young are capable of maintaining a fairly constant body temperature. A second clutch may be laid if the first is destroyed. Nests are sometimes built in telephone poles.

Helpers, offspring from the previous brood, have sometimes been noted to assist in feeding the fledglings at the nest of their parents. Cases of brood parasitism by the Asian Koel have been noted. An average breeding success of 44% has been noted with the main cause of fledgling mortality being shortage of insect food which in turn was dependent on rainfall.

Their habit of driving away predators from near their nests is believed to encourage other birds such as orioles, doves, pigeons, babblers, and especially bulbuls, to nest in the vicinity. In one study 18 of 40 nests had Red-vented Bulbuls nesting within 10 metres. An abnormal case of interspecific feeding with a Red-vented Bulbul feeding the chicks of a Black Drongo at their nest has been recorded.