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Leg morphology and locomotion in birds: requirements for force and speed during ankle flexion

A. Zeffer^* and U. M. Lindhe Norberg

Göteborg University, Department of Zoology, Zoomorphology, Box 463, SE 405 30 Göteborg, Sweden

View larger version (28K): [in a new window]   Fig. 1. (A) Cranial view of the left tarsometatarsus (proximal end to the left). The area enclosed by the broken line represents the area of insertion of the m. tibialis cranialis. (B) Diagram of the forces acting on the tarsometatarsus during flexion. FM, muscle force of m. tibialis cranialis; FO, out-force perpendicular to the long axis of tarsometatarsus; tmt, the length of the tarsometatarsus; d, the distance between the insertion of the m. tibialis cranialis and the fulcrum; d', the length of the moment arm of the muscle; , angle between line of action of muscle's tendon and tmt. See text for details.

View larger version (15K): [in a new window]   Fig. 2. Least-squares regression of loged/tmt versus logeM for 67 species of birds of different families. d, distance between the insertion of the m. tibialis cranialis and the fulcrum; tmt, length of the tarsometatarsus; M, body mass.

View larger version (10K): [in a new window]   Fig. 3. The size- and tarsometatarsus length-independent index (dindex) of the in-force lever arm for the ankle flexor (A) and the size-independent index (tmtindex) of the out-force lever arm at tarsometatarsus (B) for all species, separated into different groups. Asterisks above the data set indicate significantly higher mean values than predicted by the norm for all species (indicated by a horizontal line; *P<0.05; **P<0.01; ***P<0.001). Asterisks below the data set demonstrate significantly lower mean values compared with the norm (that is, average for all species). BOP, birds of prey; C, climbers; FS, fast swimmers; H, hangers; SS, slow swimmers; WH, walkers and hoppers.

View larger version (35K): [in a new window]   Fig. 4. The size- and tarsometatarsus-length independent index (dindex) of the in-force lever arm for the ankle flexor plotted against the size-independent index (tmtindex) of the out-force lever arm to visualize the positions for the 67 species investigated. The indices are completely uncorrelated. Some of the species are marked and discussed in the text. Ao, yellow-crowned parrot; M, the two mergansers; Mu, budgerigar; Nh, cockatiel, P, cormorant; Pe, grey parrot. For abbreviations of groups, see Fig. 3.

View larger version (16K): [in a new window]   Fig. 5. Discriminant functions (DF1 and DF2) resulting from a discriminant analysis based on the indices dindex and tmtindex presented in this study. The means for the functions of each group are marked by the abbreviation (see Fig. 3). The ellipses represent the 95% confidence interval for each group and each discrimination function. When the ellipses are completely separated, the means for the groups are significantly separated from each other as regards the indices. The solid lines represent the directions and magnitudes by which the indices contribute to the discriminant functions.