12 Jun 2012

Upcher’s Warbler Identification – Al Ali Farm (Bahrain)

Whilst ringing at Al Ali Farm in Bahrain at the weekend we caught an Upcher’s Warbler. It was caught in a mist net set between a long stand of trees and was a new ringing species for Nicole so she ringed the bird. The species breeds from Turkey eastwards to Kazakhstan and winters in Eastern Africa from Eritrea to Tanzania. I took a few photos and looked at it closely in the hand as it was nice to see clearly the main identification pointers separating it from Eastern Olivaceous Warbler.
Upcher's Warbler

When you have seen them a few times they become reasonably obvious but when seeing one for the first time, or out of range, they are slightly confusing. The main identification points are that Upcher’s Warbler is generally bigger and has a more stocky appearance although this can be difficult to judge on a lone bird if unfamiliar with them. Wings, legs, tail and bill are all longer on Upcher’s Warbler than on Eastern Olivaceous Warbler with the legs and bill being thicker on Upcher’s Warbler. I photographed a number of features that are useful in identification of the species and these are shown below. The tail on Upcher’s Warbler is long and ‘full’ and darkens towards the tip, which is not the case in Eastern Olivaceous Warbler. This darkening of the tail can be seen clearly in the below photograph. The tail is also moved in a rather lazy swinging motion often sideways and also upwards and is also fanned, which is not often if ever shown by Eastern Olivaceous Warbler. The exaggerated tail movements of Upcher’s Warbler are often the first thing that draws attention to the species, especially if they are deep in cover.
Upcher's Warbler

The wing is fairly dark and contrasts with the mantle and also has quite a long primary projection and the wing has a pale whitish secondary panel in Upcher’s Warbler, with Eastern Olivaceous Warbler having a paler less contrasting wing with shorter primary projection and a pale buffish secondary panel which is much less obvious and more difficult to see than the panel in Upcher’s Warbler. These points can also be seen in the below photos but the secondary panel is not as clear as in some. It was more obvious in the hand than is shown in the photos but can still be seen quite clearly.
Upcher's Warbler

Another quite obvious difference is the spacing on the tertial feathers, with the tip of the middle terital closer to the outermost tertial than it is to the innermost one on Upcher’s Warbler and these being evenly spaced on Eastern Olivaceous Warbler. This is obvious from the below photograph and is surprising easy to see in the field, and if photos are taken of the bird can be even easier to tell, although care has to be taken with photos due to angle of bird, displaced feathers etc.
Upcher's Warbler tertial patern
The general plumage of Upcher’s Warbler is quite greyish, rather than the brownish and yellowish tone of Eastern Olivaceous Warbler and the lores appear quite bare on Upcher’s Warbler. Lastly the bill is relatively stout looking and has a pale pinkish base on Upcher’s Warbler, see photograph below, and is less stout with a yellowish base on Eastern Olivaceous Warbler. Below are two photographs with the top one an Upcher's Warbler and the bottom one an Eastern Olivaceous Warbler for comparison.
Upcher's Warbler

Eastern Olivaceous Warbler