Yellow-vented Bulbuls ‘rain dance’ – an answer at last?

The phenomenon of the Yellow-vented Bulbuls (Pycnonotus goiavier) darting out of a tree canopy after a heavy downpour, termed “rain dance” by Lena Chow was first discussed in August 2006. At that time there were no images to illustrate the account. Lena finally managed to provide images in July 2009. The cause of this behaviour was discussed but no conclusions were arrived at.

Now, Lena has managed to video the phenomenon. You can download the video HERE.

At the same time, Jeremy Lee sent in this account of his observation on 25th June 2010: “Remember there was this discussion about YVB’s congregating in large numbers and behaving oddly?

“I saw it again, yesterday 24 Jun at about 7.20pm. Conditions were about the same as the last time I witnessed it. There was about 15 to 20 minutes more of sunlight to go before most birds called it a day.

“The first thing that caught my attention was the calls that were being made. It sounded different from the normal ‘scolding type’ notes of the bird. They were more like some sort of ‘mumbling in content’ kind of calls. I first heard it from a single bird nearby a location where two chicks just fledged. So I thought it was just some adolescent call. But I noticed that the captive adult bird at home also makes this call frequently. However I seldom hear it among wild birds.

“As I walked further I noticed that many more birds were making that same call and when I finally homed in on the source, I found more than 20 YVB clustered on the top of a date palm. They appeared to be in pairs. Instead of the usual territorial behaviour exhibited during the breeding season over the past two months, they were all singing this pleasant repertoire. They took short flights out of the palm only to make a 180º u-turn back and head straight back to the tree. This I last mistook for the birds trying to catch flying insects like termites. However this time I was very sure there were no termites and it wasn’t going to rain either. Only the timing and lighting conditions were the same.

“I walked some 100ms away from the site to play squash and realised that there were more pairs of birds joining up in flight and heading to the site.

“It looked like a congregation of all the pairs of bulbuls around the area in communal celebration of some event or end of it.

“To me it looked like it coincided with the ending of the breeding season. I don’t see any more new nests in the condo and the last nest I saw seemed to be abandoned. A female was seen still incubating the eggs last week.

“A very interesting behaviour of the YVB which I have already withnessed twice. They seem to like the palms around the estate and when they congregate in such numbers, it is quite hard for a me not to notice the calls as they are perculiar and quite loud.

“I managed to whip out my handphone to take a video clip. Can barely see the birds but at least I could record the calls made.”

On 3rd July Jeremy wrote again: “I saw the same grouping of YVB again late this evening after the rains. I was leaving the house when I noticed more YVB than usual hanging around the same palm tree. It was rather late and the birds seemed to be puffed up. Probably due to the cold weather after the rain. This gathering seems to be more frequent than I imagined. Now that I know that they frequent a particular group of trees. I will observe if it becomes a daily event and whether it continues for the next few months.”

Note: This “rain dance” phenomenon 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, it is written that: “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… The problem is that the termites may not be visible from a distance, especially when they are not present in a dense swarm. And the presence of detached wings during such swarming is not obvious since the termites are swarming above trees.

Jeremy Lee & Lena Chow
Singapore
July 2010
(Image is a grab from a video by Lena Chow)

Reference:
Wells, D.R., 2007. The birds of the Thai-Malay Peninsular. Vol. II, Passerines. Christopher Helm, London. 800 pp.

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4 Responses

  1. Amar-Singh HSS (Dato, Dr)

    Thanks for this post by Lena & Jeremy. It is a not uncommon phenomena and saw another one last week in my neighbourhood. Condition as described – post heavy/prolonged rain, late evening, mixed flock of Yellow-vented Bulbuls, Asian Glossy Starlings, Black-naped Orioles & Magpie Robins. I am convinced it is a feeding event (on termites).
    Amar

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  2. Many thanks Amar, for your comments. Just wondering -have you ever seen this at any time other than June/July (which seems to be the period such behaviour has been observed by Jeremy & myself)? Also I notice that, unlike the mixed flock that you see, I have never seen any other birds in the vicinity of the YVBs when observing their after-rain dance, although Javan Mynas, Black-naped Orioles etc abound in my neighbourhood. Thanks.

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  3. I just observed what seemed like a similar gathering this morning, at about 7.30am near Macritchie Reservoir! There were the usual Black-naped Orioles, Yellow-vented Bulbuls, Asian Glossy Starlings darting out of the trees to snatch insects from mid-air. There were also two Greater Racket-tailed Drongos amongst them.
    Is it usual for these drongos to join in such feeding sessions?

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  4. Sun Chong Hong

    Watch the Asian Glossy Starling’s version of the rain dance, performed on a hot and humid evening, recorded on 17 Apr this year, here:
    http://www.youtube.com/watch?v=1qEImq5XeUI

    I know alate termites swarm on hot and humid afternoons/evenings because my home got invaded when they do.

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