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bioRxiv2023

Migration routes and wintering sites of the Aquatic Warblers Acrocephalus paludicola breeding in Lithuania and North Belarus

For the effective protection of the globally threatened Aquatic Warbler in its entire range, knowledge of the migration and wintering areas as well as their current conservation status is of great importance. The question on where the different breeding population overwinter where (connectivity) equally important. This is also essential when new breeding populations are re-established in restored breeding sites through translocation from other, distant areas, as recently performed in Lithuania. From previous geolocator studies in central Ukraine and south-western Belarus, as well as from ringing data, it was known that these populations overwinter in Mali (Inner Niger Delta IND) and southern Mauritania. In addition, at least some birds of the NE-Polish breeding population overwinter in the Senegal delta (ring recovery). In 2018 and 2019, the migratory routes, stopover and wintering sites of two breeding populations at the north-western distribution range border in N-Belarus (29 males) and Lithuania (31 males) were investigated using light-level geolocators. All 19 recovered data loggers recorded almost complete annual cycles from mid-July to at least early April. Migration and overwintering sites of both populations did not differ significantly. Most (16 out of 19) birds also spent the winter in the Inner Niger Delta and surrounding wetlands within and around Mali. Only one bird from Belarus hiberbated in the Senegal Delta. One of the Lithuanian birds overwintered in northern Burkina Faso, another northern Nigeria. In addition, important details about the course of migration routes, timing and resting areas could be obtained. For example, the outstanding importance of Morocco and northern Algeria as resting areas on spring migration became obvious. The investigations applying geolocators resulted in a very complex and differentiated picture of the migration and stopover pattern of adult male Aquatic Warblers.

zoology↗

bioRxiv2023

Geographic distribution of feather δ34S in Europe

Geographic distribution models of environmental stable isotopes (so called isoscapes) are widely employed in animal ecology, wildlife forensics and conservation. However, the application of isoscapes is limited to elements and regions for which the spatial patterns have been estimated. Here, we focused on the ubiquitous yet less commonly used stable sulfur isotopes ({delta}34S). To predict the European{delta} 34S isoscape, we used 242 feather samples from Eurasian Reed Warbler (Acrocephalus scirpaceus) formed at 69 European wetland sites. We quantified the relationships between sample{delta} 34S and environmental covariates using a random forest regression model and applied the model to predict the geographic distribution of{delta} 34S. We also quantified within-site variation in{delta} 34S and complementarity with other isotopes on both individual and isoscape levels. The predicted feather{delta} 34S isoscape shows only slight differences between the central and southern parts of Europe while the coastal regions were most enriched in 34S. The most important covariates of{delta} 34S were distance to coastline, surface elevation and atmospheric concentrations of SO2 gases. The absence of a systematic spatial pattern impedes the application of the{delta} 34S isoscape but high complementarity with other isoscapes advocates the combination of multiple isoscapes to increase precision of animal tracing. Feather{delta} 34S compositions showed considerable within-site variation with highest values in inland parts of Europe, likely attributed to wetland anaerobic conditions and redox sensitivity of sulfur. The complex European geography and topography as well as using{delta} 34S samples from wetlands may contribute to the absence of a systematic spatial gradient of{delta} 34S values in Europe. We thus encourage future studies to focus on the geographic distribution of{delta} 34S using tissues from diverse taxa collected in various habitats over large land masses in the world (i.e., Africa, South America or East Asia). Open Research statementSample metadata are stored and available for reuse in the AviSample Network database (https://avisample.net/: AS00001-AS00117; Brlik et al. 2022b). The information on the isotopic composition and geographic origin of feather samples used to produce the{delta} 34S isoscape, predicted feather{delta} 34S,{delta} 2H and{delta} 13C isoscapes are publicly available from the Zenodo data repository at https://doi.org/10.5281/zenodo.7315567 (Brlik et al. 2022c).

ecology↗