ALBATROSSES FOLLOW THEIR NOSES

Abstract

The wandering albatross (Diomedea exulans) is an amazing seabird capable of flying for thousands of kilometres, usually gliding a few metres above sea level, on wings that span up to 340 cm. Although we have been fascinated by these huge birds for centuries, not much is known about how the animals locate their prey, especially squid, over the oceans. The study by Gabrielle Nevitt and coworkers published in the Proceedings of the National Academy of Sciences shows that individual wandering albatrosses can find food using their sense of smell; in fact, the birds can pick up a scent from up to 20 km away.Nevitt and her team set out to investigate to what degree the wandering albatrosses rely on olfactory versus visual cues when foraging over thousands of square kilometres of open sea. The team tagged 19 wandering albatrosses during brief nesting periods on Possession Island in the southwestern Indian Ocean. The animals were equipped with a small global positioning system (GPS) sensor that recorded their exact position every 10 s. In addition, a small thermometer was fed to the animals to measure stomach temperature, indicating feeding bouts. In this way, the researchers could,very elegantly, record flight behaviour (flight path and prey capture) and compare the data with the wind direction.The hypothesis was that an olfactory search would be facilitated by cross-wind flight to optimize the probability of encountering scent from a prey item. Thereafter, the animals would fly along an upwind zig-zag flight path to localize the prey. Birds predominantly using their sight to capture prey would be expected to fly more directly towards a prey item, independent of the wind direction.The researchers analysed 55 track segments and observed five distinct foraging behaviours. The authors termed the first flight pattern `direct',when there was no change in overall flight direction and the flight did not depend on wind direction, indicating that the bird was responding to visual cues. The second flight pattern was referred to as `turn', where the birds stopped flying across the wind path and turned upwind, indicating that they had caught the scent of prey. In the third flight pattern, referred to as`zig-zag', the animals zig-zagged upwind in the direction of prey, much like a dog following a trail, indicating that the birds used their sense of smell to follow the direction of a faint scent signal. The team also identified a flight pattern that they called `circle', where the bird circles the prey and finally captures it. And in the final flight pattern, which the team called`water', the animals adopted a sit-and-wait strategy, where they remained on the water's surface between prey captures.When adding up both the weight and number of fish caught using the different strategies, Nevitt and coworkers concluded that the wandering albatross uses its sense of smell to locate prey on almost 50% of occasions.Thanks to a well-designed experiment using high-precision GPS, the authors succeeded in unfolding the feeding behaviour of freely ranging wandering albatrosses – a truly outstanding achievement. As it turned out, the wondering albatrosses were much better at detecting scent than anticipated,and followed their noses 50% of the time.