Pictures show how albatrosses and killer whales share meals
Albatrosses and killer whales may seem to make strange bedfellows but researchers in Japan and the UK have discovered how these large seabirds feed alongside the ocean's biggest members of the Dolphin family. Presented in the PLoS (Public Library of Science) ONE journal, unique pictures retrieved from the cameras placed on the albatrosses' backs shed light on how these birds feed on food scraps left by the marine mammals.
The researchers from the Cambridge-based British Antarctic Survey and the National Institute of Polar Research in Japan attached a miniature digital camera to the back of four black-browed albatrosses (Thalassarche melanophrys) breeding on Bird Island, South Georgia in the Southern Atlantic Ocean.
According to the scientists, albatrosses travel for many kilometres across the open ocean to find and feed upon their prey. 'Despite the growing number of studies concerning their foraging behaviour, relatively little is known about how albatrosses actually locate their prey,' the authors of the study wrote.
By using a combined animal-borne camera and depth data logger on the free-ranging birds, the scientists effectively showed how a number of the albatrosses actively followed a killer whale (Orcinus orca) and fed on the food scraps that the huge mammal did not consume.
The Japanese group Little Leonardo Co. Ltd manufactured the innovative, lightweight camera, which was removed from the birds when they returned to their breeding ground following their food-search jaunts. The camera, with the capacity to store around 10 000 images, had depth and temperature sensors, and was 22 millimetres (mm) in diameter, 132 mm in length, and weighed 82 grams in the air (i.e. less than 2.7% of the body mass of the study's birds). A total of 28 000 images were obtained from 3 of the 4 cameras used (1 was not retrieved).
'The camera images together with the depth profiles showed that the birds dived only occasionally, but that they actively dived when other birds or the killer whale were present,' the research showed. 'This association with diving predators or other birds may partially explain how albatrosses find their prey more efficiently in the apparently "featureless" ocean, with a minimal requirement for energetically costly diving or landing activities.'
Because the camera barely affects the aerodynamic shape of the albatross, the breeding success of the birds under observation remained unchanged.
'These images are really interesting,' noted Dr Richard Phillips of the British Antarctic Survey. 'They show us that albatrosses associate with marine mammals in the same way as tropical seabirds often do with tuna. In both cases, the prey (usually fish) are directed to the surface and then it's easy hunting for the birds.'
The results of the study, part of a project conducted under the auspices of the Japanese Antarctic Research Expedition and British Antarctic Survey, formed part of the International Polar Year (ICY) 2007-09 programme. The scientists said this study can fuel further research for tracking top marine predators. New information would offer greater insight on the interaction between marine animals and their environment.