Skylark optimal flight speeds for flying nowhere and somewhere

Flight is energetically very costly. For birds the mechanicalpower in relation to airspeed is characterized by a U-shapedfunction. From this function we can derive optimal flight speedsassociated with minimum power (V_mp), minimum cost of transport(V_mr) and minimum overall time of migration (V_mt). Since flightis energetically so costly, aerial displays and song flightcan potentially serve as signals reliably indicating the individualquality or resource potential of the signaler. In order to maximizethe amount of song flight produced, we expect V_mp during songflight, while during migration we rather expect V_mr or V_mv Wecompared flight speeds of skylarks (Alauda arvensis) duringsong flight and migration flight, respectively. In this speciespredicted V_mp = 5.5 m/s, V_mr = 10.5 m/s, and V_mt = 12.1 m/s.The preferred airspeed during song flight did not differ significantlyfrom the predicted V_mp, while airspeed during migration wassignificantly higher than V_mr and Vmp indicating that flightspeed is a flexible trait that birds adjust to different situations.Why the skylarks speed up so much on migration is still unclear,but it may be that due to the shape of the predicted power curve,variation in cost of transport at high speeds is relativelysmall.