Sunday, 24 July 2011

Bird Ringing, Titchfield Haven - 23rd and 24th July 2011

Two ringing sessions this weekend and a total of 326 birds captured. As with last weekend the most notable species was Grasshopper Warbler, 47 captured on Saturday and a further 25 on Sunday. So added to the 127 that we have already ringed during July, that is an unprecedented 199 birds before the end of July, and interestingly not a single adult bird. Hopefully that is a good sign and the adults are still nesting whilst the juveniles head south.

Other species captured included Garden Warblers, Common Whitethroats and Blackcaps in low numbers a handful of Eurasian Reed Warblers, and a marked increase in the numbers of Sedge and Willow Warblers. Sedge Warbler was the most numerous species captured on both days, and in contrast to the Grasshopper Warblers, included both adult and juvenile birds. Adult and juvenile Sedge Warblers undergo a complete moult on their wintering grounds and therefore can be aged very easily during the autumn migration. Juvenile birds have an olive-brown/straw ground colour to their plumage, with fine spotting on the sides of the breast, in addition there is a paler stripe through the centre of the crown.

Juvenile Sedge Warbler

Their plumage overall is very fresh, and this is usually very evident, particularly the wing tips and the tail feathers.

Fresh Plumage of Juvenile Sedge Warbler Wing

Adult birds have a generally darker brown colouration to the upper-parts, with pale almost white underparts, which lack any spotting, and a dark crown without any hint of a stripe. The plumage is generally very abraded, having been with the bird since the previous winter.

Adult Sedge Warbler

The tips of the wing and tail feathers are usually very worn, and this is usually very obvious, as in the picture below.

Worn Wing Feathers of Adult Sedge Warbler

The Sedge Warbler is one of the commonest birds that we ring and subsequently generates a good number of recoveries. Of the birds ringed last autumn we have had news of six foreign recoveries, four from France, one from Senegal and one from Mauretania. The four French birds were recaptured between nine and 22 days after the original capture date and had travelled between 304 and 401 kilometres to the south and east. The  birds captured in Senegal and Mauretania were captured 171 and 129 days later, 4054km and 4059km south-south west, respectively.

The peak month for Willow Warbler migration is August and so it was no surprise to see the numbers start to increase. Only two birds were captured on Saturday, but on Sunday we captured 9 birds.

Head of Juvenile Willow Warbler

Juvenile Willow Warblers have strongly and evenly, yellow coloured underparts and a bold yellow supercilium. Whereas adult birds tend to have generally white underparts that are streaked yellow.

Juvenile Willow Warbler

As we carried out our ringing activities this weekend, we were aware that we were being watched, and sure enough sat in the Willows by the ringing station was a female Eurasian Sparrowhawk. A pair of birds raised a brood here this year, and the female has taken to sitting by the ringing when she returns from hunting, even though the young have now left the nest. She was paying particular interest to recently released birds so we had to be very careful about where we released them, in order to ensure that she did not catch a bird just after we had just released it.

Female Eurasian Sparrowhawk

A couple of times she sat forward as if about to launch, but soon settled back into her resting position. We will have to keep an eye on her during the autumn.

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