Fuelling strategies differ among juvenile Sedge and Reed Warblers along the eastern European flyway during autumn migration (original) (raw)
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The European Zoological Journal, 2020
The great reed warbler Acrocephalus arundinaceus is a common migrant through the Western Palearctic. However, its migration strategy, especially the spatiotemporal pattern of accumulation and utilisation of energy stores en route, is poorly known. Using ringing data collected at distant stopover sites located from Central Europe to Asia Minor, we observed that pattern in juvenile great reed warblers migrating along the eastern European flyway in autumn. We analysed body condition and stopover duration and estimated potential flight ranges for this species, taking into account two large ecological barriers-the Mediterranean Sea and the Sahara Desert-which it crosses during its southward migration. In Central and SouthEastern Europe the seasonal trends in body condition were similar and non-linear, with low values in August (i.e., during intensive migration of Acrocephalidae), and then a significant increase from the beginning of September until the end of the month. Estimated potential flight ranges showed that individuals migrating through Central and SouthEastern Europe might generally reach only the northern coast of the Mediterranean Sea. On the other hand, those flying from Asia Minor were able to reach the northern edge of the Sahel zone, crossing two large ecological barriers without refuelling. Therefore, it seems that great reed warblers change their autumn strategy en route: first, they migrate in short steps with low energy reserves through continental Europe; and then, after intensive refuelling before the Mediterranean Sea, they reach sub-Saharan Africa in a long flight. Based on the analysis of ringing data from several stopover sites, we show the complex pattern of how a longdistance migratory species accumulates and utilises its energy stores en route.
Animal Conservation, 2011
The effective conservation of aquatic warbler Acrocephalus paludicola, one of the most threatened western Palaearctic migratory passerines, requires good knowledge of its ecological needs at stopover sites. In particular, identifying its diet, which controls the accumulation of fat reserves during migration, facilitates the selection and management of adequately protected areas. Further key information includes the relationship between prey species abundance and habitats of aquatic warbler on stopover. We performed standardized mist netting in the Audierne marshes (western France) during 12 years, which resulted in the capture of 1200 aquatic warblers, and provided measurements for mass gain and the collection of faeces to infer the birds' diet. Invertebrate sampling was carried out in the three main Audierne marsh habitats (reed bed, fen mire and meadow). In order to go beyond prey digestibility bias, we also studied two closely related Acrocephalus species, present at migration stopover sites during the same period. We found that the diet composition of aquatic warbler observed at migration stopover sites is based on large-sized prey (Odonata, Orthoptera, Lepidoptera). Like sedge warblers, aquatic warblers put on weight during migration stopovers (daily mass gain = 0.38 g). This increase in weight suggests that the aquatic warblers might have adopted a strategy for long-distance migration with few stopovers only. Owing to great differences in diet, conservation management for the threatened aquatic warbler at stopover sites should not rely on existing knowledge about sedge and reed warblers. Similarities in the diet of aquatic warbler between nesting areas and migration stopover areas and the relationship between habitat and prey abundance suggest that fen mires play an important role in the quality of the foraging habitat at stopover sites.
Autumn Migration Speed of Juvenile Reed and Sedge Warblers in Relation to Date and Fat Loads
The Condor, 1999
We analyzed speed of migration in two congeneric warblers, the Reed and the Sedge Warbler, Acrocepkalus scirpaceus and A. sckoenobaenus. Sedge Warblers migrated at a higher speed than Reed Warblers. The two species showed similar rates of fat deposition at our Swedish study site, although Sedge Warblers departed with lower fat loads. The higher speed of migration in Sedge Warblers and their lower departure fat loads suggest that they encounter stopover sites which offer higher relative fat deposition rates farther south. The amount of visible fat at the time of banding was positively related to the speed of migration. Estimates of speed of migration for the two species suggest that the recoveries were situated on average 76-111 km farther south per increase in fat score, corresponding to 58-85% of the expected distance a bird can cover by using the fuel of one unit of fat score.