Wednesday, December 29, 2010

A bit more from Kenya - Mida Creek shorebird ringing

The second part of my Kenya trip was dedicated to shorebird ringing at Mida Creek with Colin Jackson and his team. Moonlight was a bit too strong, which reduced our catches, but that allowed us to process the birds with less pressure, and I was able to study some of the species in detail.
Of course the hightlight of the whole session was ringing Crab Plovers. These buggers can bite! Great birds to handle though. Hopefully these colour rings will provide new information about their seasonal movements.

I was especially interested in the identification of Lesser Sand-plovers of both forms - mongolus and atrifrons, and their separation from Greater Sand-plovers. We handled about 50 of each group, and I watched a few hundred more in the field. I must admit that I found most ID features mentioned in literature quite useless, even in the hand. Width of wingbar was very variable in both species. In some, the feature mentioned in literature, that lessers have a more even wingbar while on greaters wingbar is more prominent on inner primaries, was evident, like in the image below. However, some greaters had a much longer and broader wingbar, and in both species wingbar pattern was strongly dependent on wear. I couldn't find any difference in tail pattern and in pattern of the rump.
Lesser (above) and Greater (below) Sand-plovers

Head shape and bill shape were both very variable in both species and I found these features totally useless. Some lessers had very long, pointed bills. Some greaters had pretty rounded heads.
Lesser (above) and Greater (below) Sand-plovers
Lesser (left) and Greater (right) Sand-plovers

Look at this head shape and bill profile of an atrifrons Lesser Sand-plover. How would you describe it? More angular? Less angular? Long bill? Slender? Pointed? Developed gonydeal angle? Useless...
The only features that I found usefull in separating lessers from greaters were size, and leg colour. Lessers have black legs, greaters have green legs. 100% reliable in all the birds I checked. The problem is with dirty legs, like the KM20 bird in March had. But if you are sure you have the true leg colour - this should be the best feature.
About size: this is very usefull and reliable when you have both species together, or when you have very good experience of comparing birds side by side. In the hand it's very easy of course, but even in the field it was very easy for me after watching them for several hours. I saw no birds that were intermediate in size. I am sure such individuals exist, but must be very rare. Of course when encountering a lone vagrant this might cause a real headache, but to me perception of size (small vs. big) was straightforward and easy to apply in the field.
Reviewing all of this, I am sure that the March bird duirng the festival was a Lesser Sand-plover - sorry Hadoram for the blasphemy.
Terek Sandpiper


Thanks Colin for the great time!

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