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Reed Warblers and Migration

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Posted: Thursday 25th October 2018 by WildBlog

(c) Amy Lewis

By Lesley Cox and Richard Bland, Bristol Naturalists’ Society

In the recent weeks, millions of birds have travelled south through the countryside, along the rivers, down the estuaries, flitting silently from feeding place to feeding place, for the most part unseen, unheard and unrecorded. Yet the science of bird ringing has, over the past century, brought to light both the vast scale of migration and shown where many species are. Many have been discovered in Africa where they overwinter away from the UK. One local centre of bird ringing activity is the Chew Valley Station, where every year ringers catch thousands of warblers, especially the reed warbler, which has hundreds of pairs breeding on the reeds, including one ten-year-old member of the species that was re-trapped there this summer.

The reed warbler is a tiny, inconspicuous brown bird (between a blue tit and great tit in size) and a summer visitor to Britain. Being warm brown above and buff beneath, its plumage provides perfect camouflage as it raises its chicks amongst the reeds, but its continuous scratchy song is almost unmistakable, and cuckoos appear to locate nests to inhabit with ease. It will breed wherever reeds grow, and its numbers have increased steadily over the past few years as new wetlands have been created – some by fishermen, some by farmers, some as a result of rhynes – water-filled ditches - being abandoned. During the breeding season it is easily identified, but once the young have fledged, its song ceases and the bird effectively vanishes from sight. However, there is some evidence to suggest that increased summer temperatures are leading to second broods.

Between July and September, a partial moult takes place. This is completed in Africa and the birds become solitary as the adults’ plumage becomes greyer. During migration it can turn up anywhere, including gardens away from water, so it is wise to be alert during those months. Locally there is a population of about 1,500 pairs – over half at Chew – and surveys show a steady rise of 30% since 1994. Nationally, their greatest concentration is in the Somerset Levels and the Norfolk fens, and the last monitoring showed a 40% increase since 1968. Unlike so many bird stories, this is one of success; a vivid demonstration that, if the habitat is right, the birds will flourish.

If you would like to know more about migration, ringing, or other ways we gather the information that expands our knowledge of birds, or if you would like to come on one of our field trips, please contact the Bristol Naturalists’ Society at secretary@bristolnats.org.uk

Photo in copy (c) Martyn Pratt BNS
 

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