Monday, April 6, 2009

Albatrosses adapted to wind, feeding conditions; at risk in changing climate

A large team of researchers has found that albatross body shape and relative wing size is linked to where they nest and how far they fly to feed.

And also, how well they may adapt to changing global climate conditions.

(Image: Albatross in flight. NOAA photo by Capt. Budd Christman, NOAA Corps.)

The team found that albatross species with smaller wings compared to their body size do not generally range as far for feeding as those with higher wing-to-body ratios—and that this may limit the ability of rare species to expand their range.

The article, “Wind, Waves, and Wing Loading; Morphological specialization may limit range expansion of endangered albatrosses,” was published in the online journal PloS ONE by Oregon State researcher Robert M. Suryan, along with a team from across the country and Japan that included David Anderson, Scott Shaffer, Daniel Roby, Yann Tremblay, Daniel Costa, Paul Sievert, Fumio Sato, Kiyoaki Ozaki, Gregory Balogh and Noboru Nakamura.

Albatrosses, of course, are famous for flapless flight. They are consummate at soaring, a flight technique that requires far less energy than wing flapping. Four of the important Pacific albatrosses are all in the genus Phoebastria.

The researchers noted that a couple of the Pacific albatross species with larger bodies, the short-tailed and waved albatrosses, have the smallest breeding ranges. They tend to breed near rich feeding waters, so the don't need to go too far.

Short-tailed albatross breed on islands in the northwest Pacific near Japan and feed in the relatively nearby rich Kuroshio and Oyashio currents. Waved albatrosses breed mostly in the Galapagos and feed in the relatively nearby Peruvian upwelling.

Of the two, the short-tailed albatross has smaller wings, but operates in an area with generally higher wind speeds, which appear to help keep it aloft. When it ventures into feeding regions with lower wind speed areas, they tend to be near the nesting area, so shorter flights can make up for the energy cost of more energetic flying.

The waved albatross has much larger wings compared to its body size, which appears linked to to low wind speeds in its feeding area.

“Waved albatrosses encounter low wind speeds year-round. Fittingly, the waved albatross had aerodynamic performances more similar to smaller albatrosses, requiring less wind to stay aloft than the short-tailed, despite being similar in body size. Hence, the waved albatross appears adapted for low wind speed and wave height environment, and, indeed, is the only albatross to breed in a tropical ocean.”

Meanwhile, albatrosses with smaller bodies and comparatively large wing surface areas, fly over much larger swaths of ocean when feeding. Satellite tag studies have found Laysan albatrosses that fly thousands of miles in a single feeding trip—going as far on a single foray as from the Northwestern Hawaiian Islands to San Francisco Bay and back.

“Smaller-bodied black-footed and Laysan albatrosses primarily nest on islands in the central North Pacific and traverse large expanses of open ocean during the breeding season to feed in the sub-Arctic transition zone and along continental shelf regions of the California and Alaska Currents,” the authors said.

Among the impacts of this study is the realization that as climate change and sea level rise threaten their current nesting islands, short-tailed albatrosses won't be able to travel long distances through low-wind areas to new nesting areas, and the waved albatrosses may not be able to traverse high-wind areas.

“Restoration of remote, predator-free, and higher elevation island habitats may be particularly important for the long-term conservation of Phoebastria species; especially islands within productive continental margins for the two endangered species that show specialization for breeding in these regions,” the authors write.

©2009 Jan TenBruggencate

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