Energetic consequences of flight speeds of foraging red and hoary bats (Lasiurus borealis and Lasiurus cinereus; Chiroptera: Vespertilionidae)

We used Doppler radar readings of the flight speeds of foraging, lactating female Lasiurus borealis (N=826) and Lasiurus cinereus (N=544) to test morphologically based predictions about their flight performance. Both species flew at speeds (V=6.7 and 7.7 m s-1, respectively) that differed significantly from predicted minimum power speed (Vmp; 4.0 and 5.08 m s-1, respectively) or predicted maximum range speed (Vmr; 5.25 and 6.69 m s-1, respectively), perhaps reflecting the active pursuit of moths performing evasive manoeuvres. Estimates of costs of flight and lactation are combined with data on prey size together with encounter and capture rates to illustrate the energetic benefits accruing to these species when they forage in concentrations of insects.