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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] 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
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Seed dispersal by neotropical waterfowl depends on bird species and seasonality

Seed dispersal by neotropical waterfowl depends on bird species and seasonality

Waterbirds have an important ecological function as vectors of plant dispersal between different wetlands. In the Neotropical region, there is very limited information about this dispersal. In southern Brazil, seed dispersal by endozoochory was studied by five waterfowl, including Brazilian teal, yellow-billed teal, ringed teal, coscoroba swan, and whitefaced whistling-duck. Over 2000 diaspores were recovered from 40 different plants, including seeds of 37 angiosperms, and diaspores of mosses, ferns and charophytes. Seeds of the threatened grass Zizaniopsis bonariensis were the most abundant. The species richness and abundance of seeds dispersed varied between bird species, and between the cold and warm seasons, with a strong interaction between these two factors. 12 plant species were indicators of particular bird species or seasons. The largest bird, the coscoroba, dispersed a larger proportion of relatively large seeds. The coscoroba and the smallest bird (ringed teal) differed from each other, and from the other three ducks, in the community composition of plants dispersed. All five species make daily movements between wetlands and are widely distributed in South America, ranging from the sedentary Brazilian teal to the long-distance migratory coscoroba. informacion[at] Silva et al. (2020) Seed dispersal by neotropical waterfowl depends on bird species and seasonality.  Freshwater Biology