1. Wind energy production has expanded to meet climate change mitigation goals, but negative impacts of wind turbines have been reported on wildlife. Soaring birds are among the most affected groups with alarming fatality rates by collision with wind turbines and an escalating occupation of their migratory corridors. These birds have been described as changing their flight trajectories to avoid wind turbines, but this behaviour may lead to functional habitat loss, as suitable soaring areas in the proximity of wind turbines will likely be underused. 2. We modelled the displacement effect of wind turbines on black kites (Milvus migrans) tracked by GPS. We also evaluated the impact of this effect at the scale of the landscape by estimating how much suitable soaring area was lost to wind turbines. 3. We used state-of-the-art tracking devices to monitor the movements of 130 black kites in an area populated by wind turbines, at the migratory bottleneck of the Strait of Gibraltar. Landscape use by birds was mapped from GPS data using dynamic Brownian bridge movement models, and generalized additive mixed modelling was used to estimate the effect of wind turbine proximity on bird use while accounting for orographic and thermal uplift availability. 4. We found that areas up to approximately 674 m away from the turbines were less used than expected given their uplift potential. Within that distance threshold, bird use decreased with the proximity to wind turbines. We estimated that the footprint of wind turbines affected 3%-14% of the areas suitable for soaring in our study area.

1. Large bodies of water represent major obstacles for the migration of soaring birds because thermal updrafts are absent or weak over water. Soaring birds are known to time their water crossings with favourable weather conditions and there are records of birds falling into the water and drowning in large numbers. However, it is still unclear how environmental factors, individual traits and trajectory choices affect their water crossing performance, this being important to understand the fitness consequences of water barriers for this group of birds.2. We addressed this problem using the black kite Milvus migrans as model species at a major migration bottleneck, the Strait of Gibraltar.3. We recorded high-resolution GPS and triaxial accelerometer data for 73 birds while crossing the Strait of Gibraltar, allowing the determination of sea crossing duration, length, altitude, speed and tortuosity, the flapping behaviour of birds and their failed crossing attempts. These parameters were modelled against wind speed and direction, time of the day, solar irradiance (proxy of thermal uplift), starting altitude and distance to Morocco, and age and sex of birds. 4. We found that sea crossing performance of black kites is driven by their age, the wind conditions, the starting altitude and distance to Morocco. Young birds made longer sea crossings and reached lower altitude above the sea than adults.Crosswinds promoted longer sea crossings, with birds reaching lower altitudes and with higher flapping effort. Birds starting at lower altitudes were more likely to quit or made higher flapping effort to complete the crossing. The location where birds started the sea crossings impacted crossing distance and duration. 5. We present evidence that explains why migrating soaring birds accumulate at sea passages during adverse weather conditions. Strong crosswinds during sea crossings force birds to extended flap-powered flight at low altitude, which may 1318 |

A growing body of work shows that climate change is the cause of a number of directional shifts in the spring phenology of migratory birds. However, changes in autumn phenology are well studied and their consistency across species, as well as their link with population trends, remains uncertain. We investigate changes in the autumn migration dates of 11 species of soaring birds over the Strait of Gibraltar over a 16‐year period. Using models corrected for phylogeny, we assessed whether ecological and morphological characteristics, as well as population trends, account for interspecific shifts in migration times. We recorded different phenological changes in different periods of the migration season and suggest that these differences are due to age‐dependent responses. The variable best predicting advances in migration dates was population trend: species that did not advance their autumn migration dates were those showing a decline in their European breeding populations. We repeated our tests on a dataset representing the migration date of soaring birds across the Pyrenees Mountains and found that population trends at this site also predicted phenological shifts. Our results suggest that flexibility in migratory strategy and population trends may be related, such that different adaptive capacity in migration timing may be more relevant than other ecological traits in determining the conservation status of migratory birds in Europe and perhaps other regions.

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Understanding how soaring birds use updrafts at small spatial scales is important to identify ecological constraints of movement, and may help to prevent conflicts between wind-energy development and the conservation of wildlife. We combined high-frequency GPS animal tracking and fine-spatial-scale uplift modelling to establish a link between flight behaviour of soaring birds and the distribution of updrafts. We caught 21 black kites (Milvus migrans) and GPS-tracked them while flying over the Tarifa region, on the Spanish side of the Strait of Gibraltar. This region has a diverse topography and land cover, favouring a heterogeneous updraft spatial distribution. Bird tracks were segmented and classified into flight modes from motion parameters. Thermal and orographic uplift velocities were modelled from publically available remote-sensing and meteorological data. We found that birds perform circular soaring in areas of higher predicted thermal uplift and linear soaring in areas of higher predicted orographic uplift velocity. We show that updraft maps produced from publically available data can be used to predict where soaring birds will concentrate their flight paths and how they will behave in flight. We recommend the use of this methodological approach to improve environmental impact assessments of new wind-energy installations.