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

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