An international team of scientists has overturned an ecological study on how some animals search for food. Previously it was believed that wandering albatrosses and other species forage using a Lévy flight strategy - a cluster of short moves connected by infrequent longer ones. Published this week in the journal Nature, the team discovered that further analyses and new data tell a different story for the albatrosses and possibly for other species too.
Biologists and physicists identified 'Lévy flights', named after the French mathematician Paul Lévy, as an efficient way for animals to search for sparse food. They have been attributed to a wide range of organisms, including zooplankton, grey seals, spider monkeys and even Peruvian fisherman.
The first attempt to demonstrate their existence in a natural biological system suggested that wandering albatrosses perform Lévy flights when searching for prey on the ocean surface - a finding followed by similar inferences about the search strategies of deer and bumblebees. However, this research shows this is not the case.
Based on new high-resolution data collected from loggers attached to the legs of wandering albatrosses on the sub-Antarctic island of South Georgia, the team show that the previous claims about the Lévy flight behaviour were unfounded. They also re-analysed the existing data sets for deer and bumblebees using new statistical methods, again finding that none exhibits evidence of Lévy flights.
"It now seems the albatrosses come across food at simpler random intervals", says lead author Dr Andrew Edwards from British Antarctic Survey (now at Fisheries and Oceans Canada). "Our work also questions whether other animals thought to exhibit Lévy flights really do all forage in the same way."
This research improves scientists' understanding of the foraging behaviour of the wandering albatross -- an endangered species. It may also help develop a new theory for how animals forage -- an essential piece in the wider ecological jigsaw puzzle.
A Lévy flight is named after the French mathematician Paul Pierre Lévy and is a type of random walk in which increments are distributed according to a probability distribution with a heavy power law tail.
The wandering albatrosses inhabit Bird Island, a 5km-long rocky island off South Georgia in the South Atlantic Ocean. With no food to be found on the island, the birds undertake long foraging trips, flying close to the ocean surface to spot and feed on squid. Loggers attached to the birds' legs tell ecologists how often the birds land on the water to feed.
Estimates suggest that 300,000 seabirds are killed annually in the world's long-line fisheries, many of which are albatrosses. Since 2001, by-catch rates in well-regulated fisheries have decreased substantially, remained stable in less well-regulated ones and probably increased in pirate fisheries, for which no real data exist. 19 of the 21 species of albatross are threatened with extinction.
Reference: Revisiting Lévy flight search patterns of wandering albatrosses, bumblebees and deer by Andrew M. Edwards, Richard A. Phillips, Nicholas W. Watkins, Mervyn P. Freeman, Eugene J. Murphy, Vsevolod Afanasyev, Sergey V. Buldyrev, M.G.E da Luz, E. P. Raposo, H. Eugene Stanley, Gandhi M. Viswanathan is published in the journal Nature on Thursday 25 October 2007.
Organisations involved in this research: British Antarctic Survey, Boston University (US), Yeshiva University (US), Universidade Federal do Parana (Brazil), Universidade Federal de Pernambuco (Brazil), Universidade Federal de Alagoas (Brazil).
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