Flocking and roosting of Purple-backed Starlings

The Purple-backed Starling, also known as Daurian Starling (Sturnus sturninus), is a common winter visitor and passage migrant to Singapore. Large numbers begin to arrive in September and October when they migrate south to avoid the cold northern winter. They are also seen around March. In the late evenings these birds are known to arrive in large numbers at their roosting sites, generating loud noises with their combined cries. They make spectacular aerial displays before settling down to roost in trees.

We have been monitoring them yearly: February 2007 LINK, November 2008 LINK, October LINK and November 2009 LINK and October 2010 LINK. There was not report in 2011 but that does not mean that the starlings were not around.

In October this year, the flock is very much larger than before, estimated at between 30,00 and 50,000 birds – the largest flock ever recorded for a single location. National University of Singapore researcher Fung Tze Kwan came across these flocks on 8th September in Yishun. One week later, Wang Luan Keng and a few of her assistant researchers went and recorded these videos.

The main flock all landed on a large angsana tree (Pterocarpus indicus) that is about 12 stories high. Smaller flocks keep on arriving on to the scene, landing some distance from the main roost. After several minutes, they formed a single large flock, moving in formation, covering the entire sky and swirling around several times before also landing on the angsana tree (above). It was a spectacular sight indeed.

Besides the starlings, there were also large flocks of mynas and parakeets joining in the action. But they did not use the same tree, landing on several other trees around.

Interestingly, when we were filming the scenes, we attracted a lot of attention from passer-bys. One boy noted to his father: “Daddy, what are they doing? Look, there are a lot of birds in the sky!” Have the residents of Yishun got used to the daily ruckus of noise and the spectacular displays of the starlings in the sky above?

There are three theories why birds indulge in communal roosting: (1) The roosting site can be an information exchange centre. This has been proven by many researchers around the world working on different communal-roosting birds. Luan’s own honours project on Javan Mynas led to this conclusion. (2) Communal roosting serves as predator avoidance as there are many more birds on the look out for predators. And when a predator does arrive, the mass of flying birds would certainly confuse the predator. (3) The presence of so may birds in a tree help to provide insulation against the cold.

Some residents are in the opinion that these birds should be managed, due to the resulting noise pollution, bird faeces, etc. We would like to receive feedbacks from readers on this. Now, what if you are a resident living in the HDB block next to the angsana tree? Would you admire the aerial display and value the annual roosting of these birds as a something unique that should be left alone? Or would you call for the birds to be got rid of?

Wang Luan Keng
Singapore
September 2012