Study: Small seabird can soar like huge albatrosses

Manx Shearwater is a small black-and-white seabird that probably flies under the radar of most birdwatchers. But bird biologists know it as one of the most well-studied birds of the sea. Field studies around its primary breeding range — from Iceland to Great Britain, Ireland, France, and elsewhere in the northeastern Atlantic Ocean — began in the 1920s, and over the decades, they have revealed many of the shearwater’s secrets.

A 1953 paper on the Manx, for example, was the first to show long-range homing in a bird, thanks to a shearwater’s 12.5-day crossing of the Atlantic from Boston to Wales.

Now, a new study reveals that Manx Shearwaters have the same ability to soar as much larger albatrosses. For comparison, Manx Shearwaters measure about 12-15 inches long and have a 33-inch wingspan. Wandering Albatrosses stand as high as 4.4 feet and have the largest wingspan of any bird on Earth: 8.3-11.5 feet.

The work, published today in Science Advances, used small video cameras attached to six shearwaters to measure their flight trajectories.

During favorable wind conditions, the birds fly using a method known as dynamic soaring. Dynamic soaring is a flight technique that albatrosses famously use to glide long distances, but scientists had not previously confirmed whether other seabirds harness the technique.

The findings suggest that shearwaters possess some ability to sense wind direction, perhaps using their vision and their specially adapted tubular nostrils. The study demonstrates that these flap-gliding seabirds harvest energy from a wind gradient more effectively with increasing wind speed and that, under the right conditions, they increase the crosswind component of their flight trajectory to maximize energy-harvesting opportunities.

Dynamic soaring allows albatrosses to journey hundreds of miles across the oceans with only an occasional flap of their wings. However, it has proven challenging for scientists to observe this flight technique in other birds, particularly in seabird species such as shearwaters that routinely flap their wings as they fly.

To investigate, James Kempton of the University of Oxford and a team of 13 co-authors from Europe and Japan derived a new metric they call horizontal wind effectiveness. It measures how effectively birds’ wings harvest energy from a wind gradient. The researchers used a simplified flight dynamics model to evaluate this metric for fine-scale Manx Shearwater flight trajectories, reconstructed using video data from cameras attached to six birds.

The findings suggest that shearwaters time their vertical sequence of ascent and descent to gain energy from the wind gradient. To test whether this fine-scale behavior also occurs at larger scales, the researchers analyzed GPS data from 368 outbound foraging flights and 368 return flights for 201 birds, confirming that Manx Shearwaters do orchestrate their flights to enable dynamic soaring.

Thanks to the American Association for the Advancement of Science for providing this news.

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