Albatrosses employ orientation and routing strategies similar to yacht racers

Abstract

AbstractThe way goal-oriented birds adjust their travel direction and route in response to the wind significantly affects their travel costs. This is expected to be particularly pronounced in albatrosses, which employ a wind-dependent flight style called dynamic soaring. Dynamic soaring birds in situations without a definite goal, e.g. searching for prey, are known to preferentially fly with tail-to-side winds to increase the speed and search area. However, little is known about their reaction to wind when heading to a definite goal, such as returning to their nest. For example, returning tracks of albatrosses vary from beelines to zigzags similar to that of sailboats; however, there is no empirical test of whether the wind causes this variation. Here, based on the similar wind-dependent speed between albatrosses and sailboats, we tested whether the time-minimizing strategies used by yacht racers can explain the locomotion patterns of wandering albatrosses. We predicted that when the goal is located upwind or downwind, albatrosses should (i) deviate their travel directions from the goal on the microscale and (ii) increase the number of turns on the macroscale. Both hypotheses were supported by track data from albatrosses and racing yachts in the Southern Ocean confirming that albatrosses qualitatively employ the same strategy as yacht racers. Nevertheless, albatrosses did not strictly minimize their travel time, likely making their flight robust against wind fluctuations. Our study provides the first empirical evidence of tacking in albatrosses and demonstrates that man-made movement strategies provide a new perspective on the laws underlying wildlife movement.