Frigate birds use the power of the wind and rising air to stay airborne for many weeks at a time.
Henri Weimerskirch at the CNRS Centre for Biological Studies in Chizé, France, and his colleagues fitted great frigate birds (Fregata minor), with devices to track their movements over the Indian Ocean. Some birds were also fitted with devices to measure their heart rate and acceleration.
The researchers found that the birds stayed on the wing for up to 48 days and travelled an average of 450 kilometres daily, often tracking the wind around the edge of the huge area of low pressure called the doldrums.
The birds use a “roller-coaster flight”, the authors say, ascending up to 4,000 metres with the help of the wind and thermals. Frigates cannot land on the water, but they can glide over distances of many kilometres in a low-energy mode — sometimes with no flapping at all. This may provide them with the opportunity to nap for up to 12 minutes at a time, and allow them to stay in the air almost indefinitely.
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Wind powers weeks of non-stop flight. Nature 535, 10 (2016). https://doi.org/10.1038/535010a