Fig.4. Mid-downstroke (maximum) wingspan (A,B) decreased with increasing air speed, although for bird 1 (A) this relationship was best represented by a quadratic function and for bird 2 (B), a linear function (GLM; bird 1: F_1,8=12.54, P<0.01, r²=85.9%; bird 2: F_1,8=63.42, P<0.0001, r²=88.8%). (C,D) Mid-upstroke (minimum) wingspan (GLM; C, bird 1: F_1,9=73.37, P<0.0001, r²=89.1%; D, bird 2: F_1,8=91.09, P<0.0001, r²=91.9%) and (E,F) wingspan ratio (GLM; E, bird 1: F_1,9=67.61, P<0.0001, r²=88.3%; F, bird 2: F_1,8 =86.72, P<0.0001, r²=91.6%) also decreased with increasing air speed. Values are means ± S.E.M. At airspeeds 11ms-1 (bird 1, A,C,E) and 10ms-1 (bird 2, B,D,F) N=4. All other N=5 flight sequences.

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