Monday, 30 September 2013

Fattening up

The recent ringing sessions at Pwllcrochan and Ty Rhyg have witnessed a change from summer to autumn. At Ty Rhyg where the bulk of the catch is usually Willow Warbler and Blackcap in July and August, numbers of these species have reduced to just a handful in September. Meanwhile at Pwllcrochan near the coast in the south of the county numbers of Blackcaps are at their peak, attracted by a crop of ripe blackberries and elderberries. Some of the those ringed were weighing in at over 25g, compared to a typical Ty Rhyg weight of 16-18g during July. Their fat stores will probably get them to southern Spain without the need to stop and refuel. A late sedge warbler at Pwllcrochan on 25th Sept was also very heavy at 16g and fat stores were visible across it entire underside. Sedge Warblers are thought to cross the Sahara in one non-stop flight from northern France/southern Britain. With migrating birds, fat is good, but not all will find enough food to fuel up before the journey - a juvenile sedge warbler at Ty Rhyg in late September only weighed 9.6g and had a fault bar across the outer tail feathers where poor nutrition has retarded the feather growth during the fledging period. The chances of this one getting to Africa and back are not that good.

A fat and healthy juvenile Sedge Warbler ready to fly south
Sedge Warbler tail showing fault bar damage from a starvation
 period in the nest

Chiffchaffs are the latest of the warblers to migrate and are still around in good numbers

Goldcrest migration is more of a random dispersal during late September and October

Firecrests are autumn and winter visitors, with this one at Ty Rhyg on 29th Sept

Maybe the last Willow Warbler of the year (29th Sept)
Paul, John and Paddy

Monday, 16 September 2013

Whimbrel migration

In May we were catching and colour-ringing Whimbrel as they headed north as part of a larger project set up by Tony Cross (see ruffledfeathers)  with the aim of trying to find out more about the migration of this transient species. So far we have only had one report of the 34 we ringed in Pembs in spring, a bird which unfortunately died after colliding with electric cables before managing to leave Pembs. Whimbrel have recently been passing through on their way back from their breeding grounds further north and during four routine ringing sessions at the Gann Estuary near Dale since early August 4 individuals have been caught. This total is surprisingly low given that 1498 were counted passing Strumble Head on 18th August (see Strumble blog).

Although the sample size is small it was noticed that the autumn birds were heavier than those in spring (average of 486g compared to 410g), presumably implying that although they pass through in good numbers in autumn, they don’t need to feed up, so many must carry straight on without stopping. Anyway, if anyone is out watching Whimbrel then it is worth looking for a numbered yellow colour-ring above the knee on the right leg and a green one below, as in the photo below.

Adult Whimbrel with colour-rings

6 Curlews have also been ringed and weighed this autumn and their weights were quite a bit lower than that expected for this time of year  with an average of 646g compared to the national average of 770g in autumn (BTO website), but  the sample size is still too small to draw any confident conclusions.

The Whimbrel study has had a very interesting ‘bycatch’ with the most recent session producing 40 waders of 10 species. Half of these were Oystercatchers which generated much discussion on how to age them correctly - in the end we think we sussed it! (see photos below). Also ringed were; 4 Curlew, 4 Dunlin, 5 Bar-tailed Godwit, 2 Redshank, and singles of Greenshank, Black-tailed Godwit, Common Sandpiper and Ruff.

Oystercatcher age code 3 - born this year

Oystercatcher age code 5 - born last year

Oystercatcher age code 7 - born two years ago
Oystercatcher age code 8 -  at least 3 years old
Male and female juvenile Bar-tailed Godwits - the female has the longer bill
Juvenile Black-tailed Godwit
male Ruff 
Juv Common Sandpiper
Paddy J and Paul W