Bird Watching (UK) - - Species -

pre­dom­i­nantly of short sedges. In their core area, the river val­leys of the Biebrza in Poland and the Pripyat in Be­larus, large wet­lands re­main, but the de­cline has still been dra­matic. There, it’s not so much habi­tat loss as habi­tat change, prompted by so­cioe­co­nomic fac­tors, that’s been the prob­lem. The Aquatic War­bler’s favoured sedge-beds, tra­di­tion­ally scythed by hand for hay and thatch, have been aban­doned by an ur­ban­is­ing pop­u­la­tion. Scrub, pre­vi­ously kept in check, has taken over and sedge-beds have dried out, al­low­ing reed to be­come dom­i­nant. Tra­di­tional hand scyth­ing had largely ceased in these ar­eas by the 1990s – Aquatic War­blers in their last strong­hold were in trou­ble. A mas­sive con­ser­va­tion ef­fort was needed, com­bin­ing both sci­en­tific re­search as well as on the ground habi­tat man­age­ment. Re­cently, a ma­chine has been de­vel­oped that repli­cates the ef­fects of hand­scy­thing. This can be used to cut large swathes of marsh ef­fec­tively, with­out slic­ing off the low sedge-tus­socks that the birds nest on. Such prac­ti­cal habi­tat man­age­ment, com­bined with re­search by con­ser­va­tion sci­en­tists, has sta­bilised the core pop­u­la­tion, which is now thought to con­sist of about 12,000 singing males.

Knowl­edge gaps filled

As a re­sult of this ex­ten­sive work, some large gaps in our knowl­edge of the Aquatic War­bler have been filled. For ex­am­ple, un­til 2007 it still wasn’t known where birds spent the win­ter. It is very hard to con­serve a species when you don’t know where it spends the ma­jor­ity its life. The process that fi­nally led to birds be­ing seen in the field in Sene­gal is fas­ci­nat­ing. Molec­u­lar anal­y­sis has helped mas­sively to de­ter­mine the move­ments and trace the ori­gins of mi­gra­tory an­i­mals. The molec­u­lar com­po­si­tion, specif­i­cally the heavy iso­tope com­po­si­tion, of rain dif­fers across the globe; if you were to give the right sci­en­tist a rain­wa­ter sam­ple, they’d be able to tell you where on the planet it fell. An­i­mals in­cor­po­rate this ‘iso­topic sig­na­ture’ into their body tis­sues, through diet. Be­cause Aquatic War­blers re­grow their flight-feath­ers in Aquatic War­blers look, in some ways, like a cross be­tween a Sedge War­bler and a par­tic­u­larly streaky Grasshopper War­bler win­ter, feather sam­ples taken dur­ing the sum­mer in east­ern Europe could be an­a­lysed in the hope of re­veal­ing their win­ter­ing grounds. So it proved, when the sam­ples were com­pared with iso­topic pro­file maps of West Africa a spe­cific lo­ca­tion was iden­ti­fied: The Djoudj Na­tional Park in Sene­gal. Birds were then searched for, and seen in the field, within this park, and more re­cently other win­ter­ing sites at smaller wet­lands in Mau­ri­ta­nia and Mali have been dis­cov­ered. Un­for­tu­nately, the con­struc­tion of a river dam fur­ther up­stream of the Djoudj, has re­sulted in both the qual­ity and quan­tity of habi­tat re­duc­ing sub­stan­tially. As with many of our sum­mer mi­grants, it’s a two pronged at­tack, with both breed­ing and win­ter­ing habi­tats be­com­ing de­graded. If Aquatic War­blers are fly­ing from east­ern Europe to Sene­gal in au­tumn, why are they end­ing up in wet­lands on the south coast of Eng­land? Un­like other passer­ines head­ing to Africa in au­tumn, that take a more di­rect southerly route, Aquatic War­blers on leav­ing their breed­ing grounds travel west­ward. They ap­pear to ori­en­tate them­selves by track­ing the coast­line, firstly along the Baltic coast of Ger­many, on­wards past the Nether­lands and across the top of France, with some then end­ing up on the south coast of Bri­tain. Per­haps they are fol­low­ing a tra­di­tional route, im­printed into the ge­netic code, tak­ing in large wet­lands as stop­ping-off points, some still present, oth­ers long gone. Bri­tain’s pas­sage pop­u­la­tion is tiny com­pared to the larger num­bers that turn up in north­ern France and the Chan­nel Is­lands. Oc­cur­rences in Bri­tain are un­doubt­edly in­flu­enced by the

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