Fig. 2. Relationship between total lean dry mass and fat content in birds after a long-distance flight (Ventotene sample). Fat content was calculated as a percentage of total dry body mass. Regressions were significant in all species except the garden warbler (N=6). In the willow warbler, the length of primary 8 also explained some variability in lean dry body mass. Regression lines and sample sizes are as follows: pied flycatcher, y=2.476+0.326lnx₁ (r²_adj=0.86, P<0.001, N=9); willow warbler, y=0.641+0.082lnx₁+0.027x₂ (r²_adj=0.52, P=0.002, N=17); barn swallow, y=4.030+0.320lnx₁ (r²_adj=0.56, P=0.013, N=9), where y is lean dry body mass (g), x₁ is the amount of fat as a percentage of total dry mass and x₂ is the length of primary 8 (mm).