White-winged Tern: Breeding, non-breeding and transitional plumages
Posted by BESG on 7 July 08, Monday
Contributed by Dr Jonathan Cheah Weng Kwong
Jonathan has been monitoring the White-winged Tern (Chlidonias leucopterus) at Kranji since 2005.
In that early period when he was new to birds, he was rather puzzled by the “chocolate chip” tern he photographed and had difficulty getting it identified (below left). He now knows that it is a White-winged dressed in a transitional plumage.
The White-winged, also known as White-winged Black Tern, breeds in Siberia. It winters south, moving down the Malay Peninsula to Singapore and beyond to as far as Australia.
In Singapore, it is possible to see the bird both in its non-breeding (above right) and breeding plumages (below). The image below shows the breeding plumage, although “not quite though, judging from the white flecks on the head” – according to our bird specialist R Subaraj. Similarly, the “chocolate chip” bird at the top shows early transitional stage, as only some black feathers have developed.
Adds Subaraj: “White-winged Terns usually start arriving as migrants in September. They occur in numbers, particularly during passage, in coastal and offshore areas (and freshwater too). Numbers have declined over the years due to a reduction in foraging areas around our coastlines; such as the original Sg. Serangoon estuary where pig swill would empty out of the Sg Serangoon Kecil from the pig farms and this would attract hundreds of terns.
“Northbound return passage is often late in April/May and during that latter period is when you may have more birds in transitional or near-breeding plumage, as they moult in preparation for their return to their breeding grounds in the north.”
All images by Dr Jonathan Cheah Weng Kwong.
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Categories: Morphology, Develop., Waders
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