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Flight paths of seabirds soaring over the ocean surface enable measurement of fine-scale wind speed and direction
Edited by James A. Estes, University of California, Santa Cruz, CA, and approved June 10, 2016 (received for review December 3, 2015)

Significance
Monitoring ocean surface winds is essential for understanding ocean and atmosphere interactions and weather forecasts. However, wind measured by satellite scatterometers and buoys are spatially and temporally coarse, particularly in coastal areas. We deployed small global positioning system units on soaring seabirds to record their tracks. Seabirds were accelerated by tail winds or slowed down by head winds during flight, so their flight speed changed in relation to wind speed and direction. Taking advantage of these changes in flight speed, we reliably estimated wind speed and direction experienced by the seabirds. The wind observed by soaring seabird’s tracks complemented the conventional observation gaps in terms of both time and space, suggesting the possibility of using soaring seabirds as a living anemometer.
Abstract
Ocean surface winds are an essential factor in understanding the physical interactions between the atmosphere and the ocean. Surface winds measured by satellite scatterometers and buoys cover most of the global ocean; however, there are still spatial and temporal gaps and finer-scale variations of wind that may be overlooked, particularly in coastal areas. Here, we show that flight paths of soaring seabirds can be used to estimate fine-scale (every 5 min, ∼5 km) ocean surface winds. Fine-scale global positioning system (GPS) positional data revealed that soaring seabirds flew tortuously and ground speed fluctuated presumably due to tail winds and head winds. Taking advantage of the ground speed difference in relation to flight direction, we reliably estimated wind speed and direction experienced by the birds. These bird-based wind velocities were significantly correlated with wind velocities estimated by satellite-borne scatterometers. Furthermore, extensive travel distances and flight duration of the seabirds enabled a wide range of high-resolution wind observations, especially in coastal areas. Our study suggests that seabirds provide a platform from which to measure ocean surface winds, potentially complementing conventional wind measurements by covering spatial and temporal measurement gaps.
Footnotes
↵1Y.Y. and Y.G. contributed equally to this work.
- ↵2To whom correspondence should be addressed. Email: yonehara{at}aori.u-tokyo.ac.jp.
Author contributions: Y.Y., Y.G., K.Y., and K.S. designed research; Y.Y., Y.G., K.Y., Y.W., L.C.Y., H.W., C.-A.B., and K.S. performed research; Y.Y. analyzed data; and Y.Y. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Data deposition: Time series of latitude and longitude data of all the studied birds have been deposited in the Dryad Digital Repository, datadryad.org (10.5061/dryad.3pb86).
This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1523853113/-/DCSupplemental.
Freely available online through the PNAS open access option.