Sunday, January 15, 2012

Some Pelagic Birds Benefit From Global Warming by Bob Berwyn

                                                       A young wandering albatross. 

Wind belts pushed southward by a changing climate have benefited the wandering albatross. The giant pelagic birds are flying faster and spending less time foraging. As a consequence, breeding success has improved and the average weight of the birds has increased by a couple of pounds.

But those effects might be short-lived, according to new research published in the latest issue of Science.

“The wandering albatross Crozet population has decreased as a result of adult mortality on longline fishing in subtropical waters, especially females since they favour warmer subtropical waters in the north compared to the more southerly distribution of males,” said researcher Maite Louzao Arsuaga, who modeled albatross movement from 2009 to 2011.

“Due to the changing wind conditions, females are now foraging in more southward areas where such fishing is not that widespread.” However, the positive effects of changing environmental conditions of the last decades will not last in the future. Climate scenarios predict that westerly winds will move even further south by 2080 and wandering albatrosses might have to fly further to find optimal conditions for flying.

For the study, biologists combined data on the duration of foraging trips and breeding success over the last 40 years, as well as foraging and body mass over the last 20 years of wandering albatross (Diomedea exulans) breeding in Crozet Islands. This archipelago lies approximately in the heart of the southern Indian Ocean, halfway between Madagascar and Antarctica.

Thanks to miniaturised tracking devices, researchers were able to track the foraging movement of albatrosses up to 3,500 kilometers from the colony. They found that albatross have altered their search patterns following changes in wind conditions over the past two decades. Females used increasingly more poleward and windy areas for foraging. As a consequence their travel speed increased while the total distance covered during foraging flights did not change.

“This means that they spend less time at sea while incubating the egg and thus the breeding success increases” explains Dr. Henri Weimerskirch of the French National Centre for Scientific Research.

Researchers were surprised that both females and males have increased their body mass in one kilogram, which corresponds approximately to one tenth of their total body weight. This could be not only a result of shorter incubation periods on the nest, but also an adaptation to windier conditions.

The total population of the wandering albatross is currently estimated at around 8,000 breeding pairs. All populations have shown a decrease at some stage over the last 25 years. This endangered species is threatened primarily by incidental catch in fisheries, especially longline fishing at sea, whereas the introduction of alien species (such as rats or cats) are a key conservation threat for the species on breeding colonies.

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