Tuesday, 18 August 2015

Stealth Pipits and 'acredula' Willow Warblers

I wasn't sure if the flat calm and overcast conditions of yesterday morning (17th) would produce much in the way of a Tree Pipit movement over Billinge and initially there was no sign of any passing overhead. The bushes also seemed largely devoid of warblers so I thought I would be in for a quiet morning. However, to my surprise and relief the first net round produced 2 Tree Pipits with a 3rd bird being seen flying out of the net ride. Subsequently I did start to hear the occasional call of a Tree Pipit overhead but many more must have been moving than these calls suggested as another 11 were caught over the following 3 hours. The total of 13 ringed is the best catch so far this autumn and equals highest of last year which was achieved on 14/08/14.

A few of the Tree Pipits have been carrying passengers in the form of ticks like this bird.
I have previously noticed that migrating Tree Pipits don't call as frequently as is often thought and this allows many birds to pass by unnoticed or unidentified. If I hadn't been ringing I would have probably only recorded 7 or so flying over and certainly not the 20+ that must have been involved. Apart from the Tree Pipits there was little else around with only a few warblers being caught, seen or even heard. Although warblers were lacking in both quantity and variety this was offset by quality in the form of 2 Northern 'acredula' type Willow Warblers. These cold grey looking individuals lacked any yellowish-green tones to the upper parts or yellow and yellow wash to the supercilium or underparts as can be seen from the photos below.

This was the more cold and greyer looking of the 2 'acredula' Willow Warblers. The underparts were mainly white but with a very slight pale grey-brown wash to the under-tail coverts, flanks, upper breast and throat. Both 'acredulas' were aged as adults.
The second acredula type was almost identical to the first but with a very slightly browner hue to the upper parts.

Juv Willow Warbler (trochilus) with extensive yellow wash to underparts.
Adult 'trochilus'

Two views of the coldest 'acredula' above a juv 'trochilus'. lower left and adult 'trochilus' lower right. 
Separating the races isn't always straightforward as there are some complications caused by intergrades where their ranges meet. To make matters worse some Willow Warblers that breed in eastern Scotland are said to be greyer than your typical British breeding Willow Warblers. Having said that both of these birds look very good for 'acredula' even if it is safest and the convention to describe them as 'acredula' types in the absence of DNA confirmation. Wherever they have come from I have no doubt that it is a long way north and east of Billinge.

I returned to Billinge this morning in the hope of another good catch of Tree Pipits. Again there didn't appear to be any on the move but like yesterday they must have been in stealth mode as I ringed another 7 despite only faintly hearing one bird flying overhead. There were a few more warblers around compared to yesterday and these included the 4th Garden Warbler to be ringed this autumn. All in all two good days that had elements of both quality and quantity.

Tree Pipit. One of the magnificent 7 from today.
This morning's Garden Warbler - the 4th of the autumn.
Combined ringing totals (retraps in brackets) for 17th & 18th August 2015 were: Tree Pipit 20; Robin 1; Whitethroat 4; Garden Warbler 1; Chiffchaff  5; Willow Warbler 15(1); Goldcrest 3; Long-tailed Tit (2), Coal Tit 1; Blue Tit 1(1); Great Tit 1; Chaffinch 2; Goldfinch 1;  Linnet 1.

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