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  The gateway to Africa: What determines sea crossing performance of a migratory soaring bird at the Strait of Gibraltar?

Santos, C. D., Silva, J. P., Muñoz, A.-R., Onrubia, A., & Wikelski, M. (2020). The gateway to Africa: What determines sea crossing performance of a migratory soaring bird at the Strait of Gibraltar? Journal of Animal Ecology, n/a(n/a). Retrieved from https://doi.org/10.1111/1365-2656.13201.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0006-03DD-E Version Permalink: http://hdl.handle.net/21.11116/0000-0006-39EF-E
Genre: Journal Article
Alternative Title : Journal of Animal Ecology

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 Creators:
Santos, Carlos David1, Author              
Silva, João Paulo2, Author
Muñoz, Antonio-Román2, Author
Onrubia, Alejandro2, Author
Wikelski, Martin1, Author              
Affiliations:
1Department of Migration, Max Planck Institute of Animal Behavior, Max Planck Society, ou_3054975              
2external, ou_persistent22              

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Free keywords: animal tracking, bird migration, crosswind, ecological barriers, powered flight, sea crossing, soaring flight, thermal updrafts
 Abstract: Abstract 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. We addressed this problem using the black kite Milvus migrans as model species at a major migration bottleneck, the Strait of Gibraltar. 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. 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. 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 increase their chances of falling in the water. We also showed that juvenile birds assume more risks than adults. Finally, the way in which birds start the sea crossing is crucial for their success, particularly the starting altitude, which dictates how far birds can reach with reduced flapping effort.

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 Dates: 2020-03
 Publication Status: Published in print
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Method: -
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Title: Journal of Animal Ecology
  Alternative Title : J Anim Ecol
Source Genre: Journal
 Creator(s):
Affiliations:
Publ. Info: John Wiley & Sons, Ltd
Pages: - Volume / Issue: n/a (n/a) Sequence Number: - Start / End Page: - Identifier: ISBN: 0021-8790

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Title: Journal of Animal Ecology
  Alternative Title : J Anim Ecol
Source Genre: Journal
 Creator(s):
Affiliations:
Publ. Info: John Wiley & Sons, Ltd
Pages: - Volume / Issue: (n/a) Sequence Number: - Start / End Page: - Identifier: ISBN: 0021-8790