Ocean surface winds drive local-scale movements within long-distance migrations of seabirds |
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Authors: | María Mateos Gonzalo M Arroyo |
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Institution: | 1.Biology Department, Faculty of Marine and Environmental Sciences,University of Cadiz,Puerto Real, Cadiz,Spain;2.Fundación Migres, Complejo Huerta Grande,Pelayo, Algeciras, Cadiz,Spain |
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Abstract: | Long-distance migration is a major part of the life cycle of many seabirds. The main processes driving local movements within
those long-distance migratory movements are essentially unknown. Here, we studied detailed patterns of the movements with
respect to distance from land of the most abundant seabird species migrating across the northernmost part of the Strait of
Gibraltar and analysed how ocean surface winds influence those patterns. We did this by using visual and S-band radar surveys.
Our results show that seabirds followed lines of travel that were located nearer the coast than randomly expected. Re-sampling
techniques and comparison with additional data from ship-based counts corroborated this pattern, which was not substantially
affected by the decrease in detection at distances of up to 3,000 m. Wind direction and speed covaried with local patterns
of flight trajectories in a general manner. All the seabirds responded to headwinds by approaching the coast in proportion
to the magnitude of wind intensity. Such a change in flight patterns could be a strategy to reduce the effect of headwinds,
by approaching the coast where wind intensity was reduced by orographic factors. Under tailwind conditions, seabirds tended
to fly further from the coast, profiting from increasing winds further from shore. Our results imply that modification of
off-shore distance in relation to conditions of ocean surface winds may be an energetically advantageous strategy for migrating
seabirds. Off-shore distances were also dependent on global and local migratory behaviour of different species, but not on
flight type. |
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