Adjustable wind selectivity in shearwaters implies knowledge of the foraging landscape.

Abstract

Understanding the movements of highly mobile animals is challenging because of the many factors they must consider in their decision-making. Many seabirds, for example, are adapted to use winds to travel long distances at low energetic cost^1,2,3 but also potentially benefit from targeting specific foraging hotspots.^4,5,6 To investigate how an animal makes foraging decisions, given the inevitable trade-off between these factors, we tracked over 600 foraging trips of breeding Manx shearwaters (Puffinus puffinus; N = 218 individuals) using GPS accelerometers. By first uncovering the relationships between wind and the flapping effort put into flight, we show that shearwaters, while generally wind selective, adjust their wind selectivity, apparently balancing flight costs against the benefits of travel toward known targets. This is supported by a number of scenarios that alter the balance between maximizing flight efficiency and goal-oriented flight. First, shearwaters exhibit lower wind selectivity during homing movement when constrained to target-driven navigation toward the colony. Second, when wind speeds are low, flight costs vary little with travel direction, which shearwaters respond to by reducing wind selectivity in their outbound commutes, again favoring target-driven movement toward presumably memorized foraging areas. Finally, birds are also less wind selective during longer continuous periods of flight, presumably also associated with target-oriented movement. Our findings reveal how an animal's foraging strategy can dynamically optimize the complex trade-off between efficient travel and accessing known foraging areas, implying the incorporation of prior knowledge of the cost-benefit landscape well beyond the range of what can be detected directly.