Migratory Terns: Flocking and Communal Bathing

“For more than a month, a flock of terns, consisting mostly of migratory White-Winged (Chlidonias leucopterus) and Whiskered (C. hybridus) terns, have been staying in and around Serangoon Reservoir. Both species are winter visitors and passage migrants; spending time here to replenish their energy before proceeding with their migratory journey further. Also present were some Little Terns (Sterna albifrons), but they seemed separate from the main flock.

“In late November 2012, just before these terns gradually disappeared from the area, I chanced upon a flocking display at around 9:30 am. Instead of flying low over the water, which was their usual behaviour during foraging, they were soaring higher and higher. As they soared higher, the initial flock of a dozen terns was met by a larger flock to merge into a single flock of more than fifty birds (top and above). This flock continued to soar and flew in unity, circling a few times over the area before disappearing into the horizon. Could this be a practice, a prelude, before continuing on their long migratory journey from our shores? Or was it the actual commencement of their migratory journey?

“On the morning just a day before this flocking display, some of the terns (about 20 of them) were bathing in a flock (above and below) . They were performing communal bathing – not in small waterholes, but in the vast water body that is Serangoon Reservoir. Flying low over the water in the middle of the reservoir, they were turning and twisting, changing directions every now and then, and taking turns to dip into the water. Each dip was brief, lasting but a second or so. This alternating flying and plunge-bathing scene was repeated multiple times. They were at it for about 3 minutes before going their separate ways – some gathering on the floating buoys to dry while others went foraging.

“One week later, in early December, most of the terns had disappeared from the area.”

Kwong Wai Chong
Singapore
18th December 2012