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Oversea migration of white storks through the water barriers of the straits of Gibraltar

Soaring landbirds typically exploit atmospheric uplift as they fly overland, displaying a highly effective energy-saving locomotion. However, large water bodies lack thermal updrafts, potentially becoming ecological barriers that hamper migration. The effects of a sea surface on the migratory performance of GPS-tagged white storks (Ciconia ciconia) were assessed before, during and after they crossed the straits of Gibraltar. Oversea movements involved only flapping and gliding and were faster, traversed in straighter, descending trajectories and resulted in higher movement-related energy expenditure levels than overland, supporting the water barrier hypothesis. Overland movements at both sides of the sea straits resulted in tortuous routes and ascending trajectories with pre-crossing flights showing higher elevations and more tortuous routes than post-crossing, thus supporting the barrier negotiation hypothesis. Individual positions at both ends of the sea narrow were predicted by zonal winds and storks´ location at entry in the European hinterland, and birds did not show compensational movements overland in anticipation to subsequent wind displacements oversea. The length of the water narrow at departure shore, the elevation therein and the winds on route affected major components of sea crossing performance (such as distances and times overwater, minimum elevations, climb angles, speeds and energy expenditure), supporting the departure position and oversea winds hypotheses. In summary, this study provides a prime example at high temporal resolution of how birds adjust their behavior and physiology as they interact with the changing conditions of the travelling medium, reallocating resources and modifying their movement to overcome an ecological barrier. informacion[at]ebd.csic.es: Blas et al (2020) Overland and oversea migration of white storks through the water barriers of the straits of Gibraltar. Scientific Reports 10: 20760. DOI 10.1038/s41598-020-77273-x. See Spanish press release


www.nature.com/articles/s41598-020-77273-x
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The structure of waterbird seed dispersal networks is not mediated by functional traits

The structure of waterbird seed dispersal networks is not mediated by functional traits

Plants and their dispersers form interaction networks whose structure has important implications for the persistence and stability of the community. Frugivory is vital for the dispersal of many plants, but the dispersal interactions between plants and non-frugivorous animals, such as waterfowl, are poorly studied. In this study, the authors characterized the structure of networks for seed dispersal by waterfowl, considered whether their structure is similar to that of the networks formed between frugivorous birds and plants with fleshy fruits, and searched for functional traits of birds or plants that are important for maintenance of network structure. Data from four European community-level studies on the content of the digestive tracts of ducks and rallids, including 12 species of birds and 88 of plants, were used. Waterbird seed dispersal networks shared some organizational patterns with those of frugivores, but unlike frugivores, their underlying structure was not related to functional traits. This is likely related to fundamental differences between waterfowl and frugivores in the way they ingest seeds. Differences in the functional role of particular waterbird species for seed dispersal are likely due to other processes, such as differences in population size, movement patterns, microhabitat selection, or gut processing of seeds. informacion[at]ebd.csic.es: Sebastián-González et al (2020) Waterbird seed-dispersal networks are similarly nested but less modular than those of frugivorous species, and not driven by species ecological traits. Funct Ecol https://doi.org/10.1111/1365-2435.13657


https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2435.13657