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, lacta ting 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) th at differed significantly from predicted minimum power speed (V-mp; 4. 0 and 5.08 m s(-1), respectively) or predicted maximum range speed (V- mr; 5.25 and 6.69 m s(-1), respectively), perhaps reflecting the activ e pursuit of moths performing evasive manoeuvres. Estimates of costs o f flight and lactation are combined with data on prey size together wi th encounter and capture rates to illustrate the energetic benefits ac cruing to these species when they forage in concentrations of insects.