How fast can birds migrate?

Bird migration is typically characterized by periods of flight, when fuel is consumed, and intervening stopover periods when fuel is deposited. The resulting overall migration speed can be calculated on the basis of flight speed, rate of Furl deposition and power consumption during flight. Energy deposition rate (P-dep) can be estimated as the difference between metabolic scope and field metabolic rate during stopover. Evaluating how migration speed scales with body mass yields a declining speed with increasing mass for flapping flight (proportional to m(-0.19) ), while migration speed increases with increasing mass for soaring flight. For flapping flight, migration speed and power can be calculated according to aerodynamic theory, and in soaring flight cross-country speed can be estimated from rate of climb (when circling in thermals) and the glide polar. Power in soaring gliding flight is assumed to be a constant multiple of the basal metabolic rate (BMR). We used this approach to calculate expected speeds of migration for 15 species. For a small bird with a typical energy deposition rate (P-dep = 1.0.BMR) and using flapping flight, predicted migration speed is about 200 km/day, while a maximum energy deposition rate (P-dep 2.5.BMR) yields migration speeds of 300-400 km/day. In larger birds, migration speeds wilt be lower, ranging From 70 to 100 km/day for typical energy deposition rates to 150 to 200 km:day for maximum energy deposition rates. In large species, soaring flight gives higher migration speed than flapping flight. For large species using flapping flight, migration speed per se may restrict the potential migration distance that can be accommodated within an annual breeding migration programme.