Yellow-vented Bulbuls’ rain dance

posted in: Feeding strategy | 3

Lena Chow initiated the controversy when she posted an account of Yellow-vented Bulbuls (Pycnonotus goiavier) flying out from a tree canopy after the rain way back in June 2006. Three years later in July 2009 she posted another account, this time with photographic evidence, of the same phenomenon.

This time, Jeremy Lee responded with his experience of hearing the bulbuls singing and darting in and out of the canopy of a palm, also after a heavy downpour and around sunset.

Gan and KC Tsang suggested that the bulbuls could be catching alate termites that emerge from their nests after the rain – see termite hatch HERE. However, Lena and Jeremy failed to see any termites around at the time.

The debate this time expanded when Dato’ Dr Amar-Singh HSS related his experience in Perak, Malaysia: “…I have seen the behavior you describe many times in my neighborhood.
 Always after a heavy rain, preferably after a very hot day.
 They are eating flying insects that have been pushed out by the heavy 
rain (I think these are *ants that fly to mate).

 Although observers may say that there were no flying insects about, 
these alate termites are hard to see. But Lena’s pictures look classical of feeding behavior.
 Often I have seen the Oriental Magpie Robin (Copsychus saularis), Black-naped Oriole (Oriolus chinensis), starlings and even once, 
nightjars feeding together with Yellow-vented Bulbuls.” And “Javan Myna (Acridotheres javanicus) also,” added Margie Hall that Amar agreed.

Margie Hall has this to say: “The only explanation that I can think of that does not involve alate termites would relate to the fact that Yellow-vented Bulbuls actually roost together in large numbers, although they fly into the roosting trees singly and in pairs in the evenings and fly out singly and in pairs in the mornings and never give an outward impression of there being so many in one tree (observation). You actually have to watch a specific tree or bamboo clump or whatever over a period of time in the evening to count them all coming in to the same place.

“It could be (suggested explanation) that after a heavy rain in the evening, when there are many of them in the same tree, that they come out individually and in small groups to get the raindrops off their wings and to readjust themselves in various ways before settling in again to roost.”

Lena has added: “It seems the subject behaviour only occurs in the evening, even though the rain has stopped a few hours before. I wonder if anyone has seen this behaviour in the mornings (after night rains) or afternoons?”

Obviously the conclusion is incomplete and we need more observations. Lena will be monitoring the situation further and others as well, now that birdwatchers have been made aware of the phenomenon.

NOTE: Alate termites are winged reproductive males and females that swarm out of the colony in a nuptial flight usually during dusk and after a heavy rain.

3 Responses

  1. Jeremy

    More info on my single observation of the ‘after rain’ dance of the YVB.

    Time : At sunset. Normally after an overcast afternoon with heavy rain which meant that the birds would have been probably taking cover for a large part of the afternoon. Most of them would probably have tried to feed a little after the rain before calling it a night. This particular behaviour happened around 6.30-7pm. When the sun set low enough to send its last rays under thick clouds characteristic of heavy thunderstorms that engulf the whole region.

    The crown of the palm tree was no more than 3m from my window. I observed the birds through a slit in the curtains so as not to spook them. There was definitely no termites of any kind. If there was, I would probably have seen them and probably other opportunistic feeders like crows and mynahs would be around too. There was also not a single termite in my house that night. Normally dozens of them would be attracted by the lights in the house as well.

    All they did was sing their lungs out and display with their wings stretched. (I wish i had my camera with me but the low light condition would probably give poor shots). The birds took turns blasting off from the tree and after a short flight, almost crash back noisily into the crown – scooting another bird to do the same.

    I have observed them on many other occasions returning to roost in a large fine bamboo clump. The numbers may be the same, but the behaviour seems different. Not as skittish as above and they were not singing and displaying as wholeheartedly as in the above. It seems that there was no territorial animosity. The singing and displaying appeared more like a communal celebration (if i may call it so)

    The only additional information that I might volunteer is that this particular episode happened just at the end of the breeding season (because I rescued a fledgeling which has been permanently grounded due to a wing injury and has been given a ground job of being my standby alarm clock since). The behaviour could be triggered by the changes in hormonal levels of the birds. However this postulate need much more scientific proof.

    Till then. I am always on a look out after heavy rains when i walk around the condo observing the YVBs

  2. BESG

    Lena’s account of the bulbuls’ rain dance may find an answer in David Wells’ vol 2 of The Birds of the Malay Peninsula. On p158, describing the feeding habit of the Greater Racket-tailed Drongo: “Much food is taken in the air, including alate ants and termites, which are sometimes snatched by rocketing up vertically from an exposed perch into swarms passing overhead…” So those who believe in the alate termite theory may be right after all…

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