11 Aug 2015

Willow Warblers in the Eastern Province - Sabkhat Al Fasl

Willow Warbler Phylloscopus trochilus is a common spring passage and uncommon autumn passage migrant through Sabkhat Al Fasl that is scarce in the summer and rare in the winter. This is a change in status from Peter Symens & Abdullah H Alsuhaibany, study from May 1992 until May 1995 where they were recorded as Abundant. They are a long-distance migrant passing through the site in late spring from late March to early June and again from mid-August to October where they occurred in reeds, bushes and trees anywhere. Their migration period was later than Common Chiffchaff P. collybita in spring, with a short overlap period occurring in the last week of March and the first week of April, and earlier in autumn. Peak passage occurred during 10 April to 2 May with the latest bird trapped in the spring being 7 June. Some of the birds caught in spring had extensive amounts of fat present indicating they had fed well at the location and were about to move on. Two or three sub-species appear to occur at the site with one being the smaller, more brightly coloured olive-green and yellow nominate P. t. trochilus that breeds in Ireland, Britain and Southern Sweden south to northern Spain, central and north-west France east to Southern Poland and northern Romania and winters in sub-Saharan west Africa that was a common passage migrant. The Willow Warbler is a very variable species with as much variation within races as there is between them and are clinal across their range with acredula being very variable and intergrading with yakutensis in Siberia which was reflected in the other type seen that was the larger P. t. acredula / P. t. yakutensis. P. t. acredula breeds from Scandinavia, except southern Sweden & central and east Europe to central Siberia and winters in Africa south of Sudan and was a scarce passage migrant. Some of these birds were not very distinctive and most probably referred to acredula with the large, bulky, very brown/grey and white birds with yellow fringes to the secondaries being either P. t. acredula / P. t. yakutensis. These had wing lengths of greater than 73 mm and tail lengths greater than 56 mm and occurred in the first week of May, slightly later than the first wave of P. t. trochilus. P. t. yakutensis breeds in central and east Siberia and winters in east & South Africa and were the largest and palest race, showing virtually no yellow and very little green in their plumage, and were paler brown above and white with a greyish wash to breast. The rump and fringes to the retrices and remiges showed only a trace of olive-green and the supercillium was almost white and they had smaller bills and occasionally some streaking on the throat and upper breast. This makes it difficult to assign birds to certain races unless a clear distinctive example can be found which is best done on size and colour, but only fresh plumaged birds should be considered. Below are photos of presumed trochilus, acredula/yakutensis and acredula type birds.
Willow Warbler
trochilus type
Willow Warbler
acredula type
Willow Warbler
acredula / Yakutensis type

No comments:

Post a Comment