Fig. 4. Variation with respect to flight speed in (A) fH of barnacle geese (triangles, N=56 flights by seven birds) and bar-headed geese (circles, N=29 flights by two birds) flying in a wind tunnel without a respirometry mask and (B) _O2 of barnacle geese (triangles, N=11 flights by two birds) and barheaded geese (circles, N=11 flights by one bird) flying in a wind tunnel with a respirometry mask. The data from barnacle geese are from flights during which the fH and _O2 were not reduced as a result of the bird flying close to the trainer.