Figure 1.
Bird Flight Speeds (Ue; m/s) Plotted in Relation to Body Mass (kg) and Wing Loading (N/m2) for 138 Species of Six Main Monophyletic Groups
The lines show the scaling relationships Ue = 15.9 × (mass)0.13 and Ue = 4.3 × (wing loading)0.31 as calculated by reduced major axis regression for all species (Table 1). All axes are in logarithmic scale. Inserts show means (± standard deviations) for the six main phylogenetic groups in relation to these scaling lines. Species of the same group tend to fly at similar speeds, and phylogenetic group is an important factor to account for the variation in Ue.
Table 1.
Allometric Relationships between Bird Flight Speed (Ue; m/s) and Body Mass (kg) and between Ue and Wing Loading (N/m2)
Figure 2.
Explanation of the Variation in Mean Flight Speeds (Ue; m/s) among Bird Species by Different Combinations of Variables and Factors
The explanatory power (adjusted R2) of different General Linear Models with significant independent variables (***, p < 0.001) is illustrated. Phylogenetic group and wing loading emerge as key factors to account for the variation in flight speed among bird species. General Linear Models for all different combinations of body mass, wing loading, aspect ratio, and phylogenetic group were calculated, except combinations including both body mass and wing loading (because of the interdependence between these variables). Complex models (including combinations of variables) are presented only if the AIC improved from models based on single independent variables [17]. This applied only to the model incorporating both phylogenetic group and wing loading. ΔAIC indicates the difference in AIC score from the most effective model (with ΔAIC = 0). Test statistics were as follows (in parentheses) for model including mass (F1,136 = 20.0, p < 0.001), aspect ratio (F1,127 = 28.6, p < 0.001), wing loading (F1,127 = 122.6, p < 0.001), phylogenetic group (F5,132 = 34.5), and phylogenetic group plus wing loading (F6,122 = 39.6, p < 0.001).