Friday, January 07, 2011

3 January 2011: At sea off Tanjung Dawai, Kedah

Our first pelagic foray for a while was windy and overcast, with frequent showers through the day. This made for nice dull light to pick up some of the plumage subtleties of the many terns on show.

Variety of species was in short supply, with only five species putting in an appearance - Common, Little, Black-naped, White-winged and a lone Greater Crested. This was our first blank trip for Bridled Terns.

Terns on patrol as the net is drawn in.

Common Terns lived up to their name, being overwhelmingly the most numerous species.

Last year's young are now looking quite worn.

The clear grey median coverts and scapulars are new, as the bird is beginning its moult into 'first summer' plumage.

This adult has fresh inner primaries and outer secondaries, while the remainder of both are extremely worn.

Birds at this stage of moult, with very worn, blackish secondaries, can show a dark secondary bar on the underwing, a feature which is supposed to be diagnostic of Aleutian Tern, so care is needed!

This effect is not so prominent in birds which have already replaced most of their secondaries and primaries.

Rump colour seems very variable in these birds, from white, to white with a grey centre, to entirely concolorous with the back on the darkest birds.

Grey rumps were seen on both worn and fresh-plumaged birds. Grey rump is often cited as a way of distinguishing White-cheeked Tern from Common. It seems that this isn't a reliable fieldmark in the case of these eastern races.

Incidentally, check out the bill on this same grey-rumped bird! It looks orange! However, the bill is clearly also deformed (the tips of the mandibles don't meet) and I've seen quite a few of these Common Terns with misshapen bills which are generally also discoloured orange or yellow. I've commented in previous posts that this seems to be rather a common deformity in Common Terns here. So - just a Common, but could easily have passed for something rarer on brief fly-by views!

Another common bill pattern variant - this time mimicking the pattern of Sandwich Tern!

Having a mid-air preen!

There were a few Little Terns about.

This is another species where rump colour is often quoted as an important way to distinguish it from a similar species. In this case, Little Tern supposedly has a white rump, and Saunder's has a grey rump. However, once again, careful looks are needed before jumping to conclusions! All Little Terns I've seen well enough to check here have grey rumps.

There were a couple of hundred White-winged Terns, looking very dumpy compared to the 'Sterna' terns.

Black-naped Terns are the epitome of grace and beauty! Against a dark grey sea and colourless sky, it was quite difficult to get well-exposed shots though.

Some of my efforts!

See here for Mun's account of the day.

1 comment:

John Holmes said...

The light direction may be highly variable, but the exposures can be fairly consistent with manual exposure ?