Few wind tunnel studies of animal flight have controlled or corrected
for distortions to behaviour, physiology or flight aerodynamics repres
enting the difference between flight in the tunnel and flight in free
air. Aerodynamic correction factors are derived based on lifting-line
theory and the method of images for an animal trying freely within clo
sed- and open-section wind tunnels; the method is very similar to that
used to model flight in ground effect, and as in ground effect the co
rrections to induced drag may be substantial. These correction factors
are used to estimate bound wing circulation, drag and mechanical powe
r for comparison with free flight, and to derive testable predictions
of optimum flight strategies for an animal in a tunnel. In an open-sec
tion tunnel, mechanical power is increased compared to free flight, an
d the animal should try at the tunnel centre. In a closed tunnel mecha
nical power is usually reduced, and substantial savings are available,
particularly at low speeds, if the animal flies close to the tunnel r
oof. Anecdotal observations confirm that birds and bats adopt this str
ategy. The mechanical power-speed curve in a closed tunnel is flatter
than the curve for free flight, and this may explain the flat metaboli
c power-speed curves for birds and bats obtained in some measurements.