Thursday, January 27, 2011

23 January 2011: Sarawak Waterbird Survey - Sejingkat ashponds

Today we went to count the ashponds photographed here. The main roost is in the large, half-filled pond this side of the road (looking from the helicopter).

It's a major roost for curlews and greenshanks, and, as curlews are among the shiest of waders, we went early and set up a hide for the three of us. The weather was decidedly better today, and we had the sun behind us.

The birds accepted the hide as part of the scenery and came in pretty close.

Before the roosting waders arrived however, we had some time to observe the species which habitually feed at the ponds.

The Black-winged Stilts were distinctly different in both plumage and vocalizations from birds in the Peninsula. Compare the plumage of these birds with these, photographed in Penang recently. The calls heard were a high-pitched piping, lacking in the nasal, trumpeting quality of West Malaysia birds. This doesn't necessarily mean that these birds are a different subspecies, as the differences could be clinal, but it does at least suggest that these birds are a relatively distinct population from the Peninsula birds.

Marsh Sandpiper (right) and Common Greenshank (left) numbers were greatly augmented by birds coming in to roost, but there were a few which evidently remain at the ponds to feed. The two species are similar, but are readily separable by size, structure, plumage and call.

The Marsh Sandpipers were feeding on dragonfly larvae. Can anyone identify the species?

We counted 337 Common Greenshanks. There were also two Nordmann's Greenshanks, but they kept to the far side of the pond (typical!) with the Grey Plovers.

The only Common Redshank seen (right)!

Curlews were the most numerous group present. In West Malaysia, among a roost of 6,000 at Kapar, you're lucky to see one or two Eastern Curlews. Here, the situation is reversed. We counted 541 Eastern and just 63 Eurasian Curlews.

The two are easy to tell apart in flight, as the rump and back are white in Eurasian and brown in Eastern.

The same colour scheme is reflected from below - Eurasian (left) has glistening white underwing coverts and a white leading edge to the wing; Eastern has a well barred underwing.

So these are all Eastern.

Once they've landed it's a bit more challenging, but the base colour of Eurasian's plumage is distinctly paler than most Easterns, and in particular, the white vent usually stands out. I can see six Eurasians in this lot.

More subtle differences can be made out at close range. The rear flanks have drop-shaped dark shaft streaks on Eurasian, whereas these feathers have quite prominent transverse barring on Eastern. Also, all the upperpart feathers have much more prominent barring on the feather edges on Eastern than on Eurasian, and this is particularly obvious on the tertials. This last feature can be obvious at a surprising distance.

Eurasian Curlews have a whitish base colour to the supercilium, and two 'eyebrow spots' are usually obvious when the bird is sleeping face-on, whereas, on Eastern, the face pattern is relatively unmarked.

It's commonly said that Eastern Curlews have longer bills than Eurasian, and while this may be true on average, there's such variation in bill length that it isn't a good field character.

Check the difference in bill length between these two Eastern Curlews!

The Eurasians stand out obviously in bright sunshine.

Much less so when the sky is overcast. How many can you make out here?

Eastern Curlews are the largest migratory waders in the world. This one dwarfs a Common Greenshank alongside.

Some more Eastern Curlew portraits.

And a summary of the differences between Eastern and Eurasian to conclude.

For details of how you can volunteer to take part in the Sarawak Waterbird Survey, see here.


Sandakanbirds said...

hi dave, thanks a lot for commenting and giving me the right name of the birds :) in my blog, i look forward to take more picture of the waders here in sandakan and will post them in my blog and will need you help to help me to id them cos i am a beginner to the waders thanks an very nice pic in you blog :)

digdeep said...
This comment has been removed by the author.
digdeep said...

Happy to help Hamit!


Wong Tsu Shi said...

Thanks for the excellent account on the Eurasian and Far-eastern Curlews, Dave.

jytou said...

wow, love ur confusion species table. Will spend some time reading it later, happy to see some of your new entries finally.