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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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Different responses to climate change in resident and migratory birds

Different responses to climate change in resident and migratory birds

The adjustment to climate change and the differential effects of temperature on resident and migratory birds were studied using the start dates of the laying in ten long-term studies in nest-boxes in Europe with data on at least one species of resident tit ??and one species of migratory flycatcher. Resident tit populations advanced their breeding more strongly in relation to temperature increases than migratory flycatchers. The divergence was strongest in the lower latitudes where the interval between tits and flycatchers is smaller and winter conditions are more favourable for residents. The phenological adjustment of flycatchers to climate change seems to be progressively further hampered by competition with resident species. The differential effect of climate change on groups of species with superimposed reproductive ecology affects the phenological interval between them, impinging on interspecific interactions. informacion[at] Samplonius et al. (2018) Phenological sensitivity to climate change is higher in resident than in migrant bird populations among European cavity breeders; Global Change Biol