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Bayly N.J.,The Wetland Trust | Rumsey S.J.R.,The Wetland Trust | Clark J.A.,British Trust for Ornithology
Journal of Ornithology | Year: 2011

The bi-annual crossing of the Sahara desert is a considerable energetic challenge faced by approximately a quarter of Europe's total bird population, as they migrate to and from sub-Saharan non-breeding grounds. Where, when and how migratory birds prepare for the crossing remains to be defined in many species, especially in sub-Saharan Africa. Here, we describe the migration and fuelling strategies employed by the Grasshopper Warbler Locustella naevia during the northern autumn and spring to cross the western Sahara using ringing datasets from Portugal and Senegal. Body masses in recaptured birds combined with flight ranges suggest that <10% of birds in Portugal could have reached sub-Saharan Africa without refuelling. Estimated rates of mass change [up to 3. 4% of lean body mass (LBM)/day] and stopover durations (mean 8 days) also suggest that the average bird in Portugal required further stopovers, and point to the strategic importance of northwest Africa during autumn migration. In sub-Saharan Africa, Grasshopper Warblers began to leave Senegal as early as mid-January in order to spend up to 2 months at unknown sites in North Africa. Fuelling for the northward journey across the Sahara was characterised by a slow fuelling rate (1% LBM/day) and long duration relative to Portugal (19 days). The constraining factor on fuelling rates in Senegal is hypothesised to be low resource availability associated with the Sahelian dry season. These resources appear to vary annually with Sahelian rainfall, resulting in variable fuel loads and fuelling rates and potentially leading to fuelling shortfalls in years of low rainfall. © 2011 Dt. Ornithologen-Gesellschaft e.V. Source

Bayly N.J.,The Wetland Trust | Rumsey S.J.R.,The Wetland Trust
Ringing and Migration | Year: 2010

The migrator y strategies of trans-Saharan migrant passerines have generally been well described in Europe, whilst strategies south of the Sahara have received relatively little attention (Ottosson et al 2001, 2005). Given the strong link between population fluctuations and climatic conditions in the Sahel region of West Africa (Newton 2004), knowledge both of the regions occupied during winter and of the sites used during migration is essential if we are to understand population-limiting processes. In particular, the regions or sites used in preparation for crossing the Sahara Desert during spring migration, which generally requires large fuel loads (Wood 1989), may be vital to the success of migration and even carry over into reproductive success (Newton 2004). Amongst migratory passerines the ecology of the Garden Warbler Sylvia borin has been well studied (eg Bairlein 1991, Schaub & Jenni 2000) and a growing body of information details the migration of this species in West Africa (Ottosson et al 2005, Smith 2007). To add to one of the most complete pictures for a migratory passerine in sub-Saharan Africa, we present a brief summary of current knowledge and compare it to data collected in Senegal by the Wetland Trust. © 2010 British Trust for Ornithology. Source

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