Optimal trajectories for the short-distance foraging flights of swans

Optimal flight theory relates body measurements (wing span, body cross-sect ion, body mass) and aerodynamic variables (air density, drag, profile and i nduced power ratios) to the most energy-efficient velocity for long distanc e migration. For short-range (2-10 km) foraging flights the theory is expan ded to include non-negligible costs for take-off and energy savings/losses for climbing to altitude (drag decreases with air density and therefore wit h altitude). The theory predicts clear differences between Tundra and Trump eter swans. Generally speaking, for flights between 2 and 10 km Trumpeter s wans can be expected to fly approximately 5-10 m lower in altitude and 1-2 m s(-1) more slowly than Tundra swans. Moreover, the total energy required for these foraging flights is approximately 150% larger for a Trumpeter tha n a Tundra swan (80 vs. 120 kJ of direct mechanical energy for a 5 km fligh t), suggesting that Trumpeter swans may be less inclined to take-off than T undra swans. These factors indicate that even Trumpeters native to the area (as opposed to recently translocated) would be more vulnerable to hunting than native Tundra swans. The expanded theory is compared to observations m ade in Utah's Bear River Migratory Bird Refuge. (C) 2000 Academic Press.