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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 Atlantic trade winds regulate the arrival of migratory birds to the Canary Islands and the reproduction of falcons

The Atlantic trade winds regulate the arrival of migratory birds to the Canary Islands and the reproduction of falcons

Large-scale environmental forces can influence biodiversity at different levels of biological organization. Climate, in particular, is often associated with species distributions and diversity gradients. However, its mechanistic link to population dynamics is still poorly understood. Here, the full mechanistic path by which a climatic driver, the Atlantic trade winds, determines the viability of a bird population is unravelled. The breeding population of Eleonora's falcons in the Canary Islands was monitored for over a decade (2007–2017), and different methods and data to reconstruct how the availability of their prey (migratory birds) is regulated by trade winds were integrated. GPS allowed tracking foraging movements of breeding adults, weather radar was used to monitor departure of migratory birds, and an individual-based, spatially explicit model simulated their migration trajectories. Results demonstrate that regional easterly winds regulate the flux of migratory birds that is available to hunting falcons, determining food availability for their chicks and consequent breeding success. By reconstructing how migratory birds are pushed towards the Canary Islands by trade winds, most of the variation (up to 86%) in annual productivity for over a decade is explained. This study unequivocally illustrates how a climatic driver can influence local-scale demographic processes while providing novel evidence of wind as a major determinant of population fitness in a top predator. informacion[at]ebd.csic.es: Gangoso et al (2020) Cascading effects of climate variability on the breeding success of an edge population of an apex predator. J Anim Ecol https://doi.org/10.1111/1365-2656.13304


https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/1365-2656.13304