Monday, 14 February 2011

Separating yellow legged gull and Caspian gull is a mug's game

One of the most confused pictures of the UN winter wetland surveys over the last few years has been its counts of yellow-legged gull and Caspian gull.

They always find a hundred or so yellow-legged gull at Farwa in the far north west of the country and only few more as you travel eastward for 800 kilometres all the way to the coast south of Benghazi. There and further east in (Cyrenacia) the numbers are considerable but fluctuate wildly. 

It appears that the fluctuations are mainly due to two factors. One is the difficulty in separating yellow-legged gull and Caspian gull. The second is whether the UN winter count visits the wetlands east of Derna. If they visit the far east overall numbers are higher.

yellow legged gull or Caspian gull

I came across about 80 gulls at a rubbish dump just off the main Derna to Tobruk road. I have to admit I still can't separate the two species.

For example the bird above is unstreaked on the head like a Caspian gull but it has light eyes like all yellow- legged gull and which only 25% of Caspian gull have. Furthermore I have a good enough picture of another gull to tell it too has light eyes. That is only a one in eight chance of this happening if the birds are Caspian gull.

 gulls at the dump

On the other hand the red on the bill in both birds is clearly restricted to the low mandible. This is a feature of a Caspian gull. The wings also look very long another feature of a Caspian gull. For once I really can't tell. I admit temporary defeat!

gulls in the air near Derna to Tobruk road

The rubbish dump had other, less intriguing inhabitants. There were plenty of starling and a couple of common raven (which really is common on the Jebel Akhdar and here).

raven and starlings

I really like the way cattle egret get stuck into rubbish! They are a guarenteed bird of dumps in most of Libya.

cattle egret

Other species were stonechat, black redstart, and white wagtail which relish the insect life around.  Soon they will depart and the passage is around the corner.

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