Greater Racket-tailed Drongos associating with Dusky Langurs
The apparently odd relationship
Drongos
Drongos and especially Racket-tailed Drongos have been called, thugs, thieves and tricksters or are they just vocally gifted and very intelligent. |
| Fork-tailed Drongo |
The drongos are a family, Dicruridae, of birds of the Old World tropics. The 29 species in the family are placed in a single genus Dicrurus.
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 or on the ground. Some species are accomplished mimics and have a variety of alarm calls, to which other birds and animals often respond. There is evidence that they utter hoax alarm calls that typically scare other animals off food, which the drongo then eats. This phenomena is a matter of interest to researchers.
When breeding two to four eggs are laid in a nest high in a tree. Despite their small size, drongos are aggressive and fearless, and will attack much larger species if their nest or young are threatened.
Several species of animals and birds respond to drongos' alarm calls, which often warn of the presence of a predator. 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. A video of this trickery can be seen here. They not only use their own alarm calls, but imitate those of many species, either their victim's or that of another species that the victim responds to. If the call of one species is not effective, perhaps because of habituation, the drongo will try another; 51 different calls are known to be imitated.
 |
| Greater racket-tailed Drongo in flight |
The greater Racket-tailed Drongo Dicurus paradiseus is a medium-sized Asian bird which is distinctive in having elongated outer tail feathers with webbing restricted to the tips. They are conspicuous in the forest habitats, often perching in the open and by attracting attention with a wide range of loud calls that include perfect imitations of other birds. It has been suggested that these imitations may help in the formation of mixed-species foraging flocks, also known as bird waves by birders and bird photographers. Specifically this is when a consortium of different insect feeding birds move through the forest, foraging together.
Distribution
The Greater Racket-tailed Drongo is a resident breeder in tropical southern Asia, from Kashmir, India and Sri Lanka, East to Indonesia. The species is usually found in broadleaved forests and is rated of 'least concern' in the IUCN rating system.
 |
| Head feathers of Drongo paradiseus. There are regional variations |
 |
| Greater Racket-tailed Drongo in flight |
 |
| Lesser Racket-tailed Drongo (Dicrurus remifer) |
Reproduction
Greater Racket-tailed Drongos nest from March to June depending on their location. The nests are saucer-like in shape. They are made of intricately intertwined roots and leaves with fine materials lining the inside. The nests are held together by cobwebs and camouflaged with lichens and often found in the horizontal fork of two branches. The species lays 3-4 eggs, there is 15-17 days until hatching, the average fledging time is 19 days and the time to independence is 4 to 6 weeks.
 |
| Comparing nests; Greater on the left Lesser on the right |
Nesting duties, constructing the nest, incubation and rearing young are shared between males and females. Both adults will also watch over the offspring when they have left the nest.
Calls/Mimicry
 |
| Greater Racket-tailed Drongo singing. Note the yellow wing tip. |
The calls of the Greater Racket-tailed drongos are extremely varied and include monotonously repeated nasal sounds as well as more complex notes and imitations of other birds. They can begin calling around 4 am in moonlight often with a metallic tunk-tunk-tunk series. They have the ability to accurately mimic alarm calls of other birds that are learnt through interactions of mixed-species flocks. This is quite unusual as avian mimicry has hitherto been believed to be ignorant of the context of the imitated vocalisation. It is analogous to a human learning useful short phrases and exclamations in a number of foreign languages and using them in the correct context.
A range of the Racket-tailed Drongos calls can be seen in the video shown here.
Feeding
Greater racket-tailed drongos feed on the nectar of plants but also eat insects including ants, bees, beetles, dragonflies, locusts, mantids, moths and termites. Like other drongos they catch their prey in mid-air or pick them off surfaces and then carry them back to the nest in their claws. In some places they have been found to be kleptoparasitic (taking food from another bird) on others in a mixed-species flock, particularly Laughingthrushes but they are most often involved in mutualistic and commensal relationships. Several observers have found this species associating with foraging woodpeckers and there is a report of one following a troop of macaques.
 |
| Eating a captured (or stolen) insect |
 |
| Drinking nectar |
Both the Chestnut-crowned and Chestnut-capped Laughingthrushes are often in bird waves and have been observed to be victims of Drongo thievery.
 |
| Chestnut-capped Laughingthrush |
 |
| Chestnut-crowned Laughingthrush |
 |
| Shadowing a Lesser Flameback Woodpecker who is hunting for grubs |
Aggression
There are many accounts detailing the aggression of Racket-tailed Drongos. They don't seem to worry about size difference when attacking another species. I have seen them knock a Dollarbird of its hawking perch and there have been descriptions of them attacking raptors. One account has a single Drongo attacking two Great Hornbills in flight and actually riding on the back on one for several seconds.
 |
| Dollarbird |
 |
| Great Hornbill (female) |
THE NOVEL INTERACTION BETWEEN GREAT RACKET-TAILED DRONGOS AND DUSKY LANGURS
The biology and habits of a local troop of dusky Langurs has been covered in a previous two-part blog. This interaction could only occur in the range of the Dusky Langur, which is much more restricted than the Drongo. This primate is confined to Peninsular Malaysia with a slight spillover into Thailand and Myanmar.
 |
| Dusky Langur portrait |
Observations
I and others photographing or observing Dusky Langurs have noticed the often close association with Greater Racket-tailed drongos. The drongos get very close to the feeding langurs and get very excited in their presence. I have seen drongos apparently shaking with excitement in the presence of Dusky langurs. At times they appear to be conducting operations as the Langurs make their way through the forest.
 |
| Eight Dusky Langurs feeding in an Acacia tree |
 |
| A Greater Racket-tailed drongo directing operations in the same tree |
 |
| Another drongo on the same tree |
 |
| Almost always present when Langurs are feeding |
 |
| Sometimes there are 2-5 drongos present. |
 |
| On another occasion a Drongo sits patiently (top left) while two langurs take a break from foraging. |
Before analysing this phenomena we need to discuss mixed-species flocks or bird-waves
It is not uncommon to find birds of several species flocking together. One reason may be that such flocking increases the number of eyes and ears available to detect predators and may confuse them as many individuals flee at once. Also a mixture of species can take advantage of different abilities. Just as nearsighted zebras with keen hearing associate on African plains with species such as wildebeest and giraffes with keen eyesight.
Next to predator defence, however, the most popular hypothesis to explain the formation of mixed-species flocks is an increase in feeding efficiency. Flocks may function to overwhelm territorial defences, because moving groups are able to feed in areas from which single individuals would be ejected by the "owner" of the territory. Having more individuals searching for food also increases the likelihood that a rich feeding patch will be located. By moving together in a mixed-species flock, birds with the same sorts of diets can avoid areas that have already been searched for food. Individuals in mixed flocks can also learn about new food sources from other species; Finally, by associating with birds of different species that have somewhat different food preferences and foraging techniques, each individual faces less competition than it would in a similar flock of conspecifics.
Flocks may occur because one species, in the course of its feeding, flushes prey that can be caught by the others. Such foraging associations are called commensal feeding. In Australian rain forests, Yellow Robins follow Brush Turkeys, pouncing on insects the turkeys stir up as they scratch through the dead leaves of the forest floor. Cattle Egrets "flock" with cattle and tractors for similar reasons.
 |
| Cattle Egrets following a tractor |
 |
| Cattle Egrets following an elephant |
 |
| Cattle Egrets around.....cattle |
There are other interesting aspects of mixed-species flocks. For instance some species appear to take the lead in forming the flock -- to serve as "nuclear" or "core" species. Such species often have conspicuous plumage or behaviour. The Drongos fit this category.
What is going on with the Drongos and the Langurs?
The drongos are using the movement of the langurs through the forest as a greatly scaled up bird-wave. The Langurs do not move through the forest on tip toes or with any delicacy. They somewhat rampage through the forest as they jump from tree to tree.....and this disturbs a lot of insects. In other terms the Langurs are the tractors, elephants or cattle for the drongo (Cattle egrets) unearthing insects that the drongos alone cannot access.
Images with langurs and drongos are hard to obtain.
 |
| The langur is clearly aware of the drongos presence |
 |
| Greater racket-tailed drongo catching flying insects above the feeding langurs |
 |
| Overflying more foraging langurs |
What do the Langurs derive from the association?
Is the relationship commensal (commensalism is a long-term biological interaction in which members of one species gain benefits while those of the other species neither benefit nor are harmed) or mutualistic (Mutualism describes a type of mutually beneficial relationship between organisms of different species)?
The Langurs use vocalisations to communicate with each other and they have an alarm call when various predators are sighted. The Drongo knows this too and acts like an aerial recognisance system for the troop. I have seen 5-6 drongos sometimes associated with a troop. It is like having 5-6 surveillance drones without the worry of them crashing.
I have also seen drongos leading langurs to fruit or flowers (they eat both) and I wonder if there is some scouting done by the drongos or they figure flowering trees have lots of associated insects..
At other times when I try to locate where the langurs are I listen for the calls of the drongos. If they don't know the langur location they will post members at various points as a detection system. The relationship, while symbiotic, is a good example of mutualism where both organisms obtain benefit from the association.
 |
| Part of the rainforest where the interactions were observed and recorded. |
Drongo notes;
The common whistle note that is made by by the Racket-tailed Drongo leads to a local name in many parts of India of kothwal which means 'policeman' or 'guard', who both use a whistle that has a similar note.
In Australia the term 'drongo' is applied to a loser or a fool. This term comes from a racehorse in Victoria in the 1920s who raced 37 times for no wins (5 seconds and 7 thirds). The horse was named 'Drongo' after the Australian bird species the Spangled Drongo and word spread around regarding its inability to win. It seems a little unfair as the races the horse ran in were all top class events. In fact a 'drongo' should be a term for a smart and fearless person.
Pretty good post. I just stumbled upon your blog and wanted to say that I have really enjoyed reading your blog posts. Anyway, GLOCK 45 FOR SALE I hope you post again soon. Big thanks for the helpful info.
ReplyDelete