Fig. 6. Toughness (T) as a function of fractional distance (d) along the feather, where `0' represents the proximal end and `1' represents the distal end of the feather. There were no significant differences in slope (P_2,153=0.76) or intercept (P_2,153=0.22) between barb colors (overall equation: T=-10d+15, r²=0.19, P_1,154<0.001 that the overall slope is zero).