Fig. 4. The time required to land on the nest, relative to appearing in the camera view, for bees at different light levels. Upward triangles denote morning flights, downward triangles denote evening flights. The dotted line is a linear regression for all the data (on log-transformed intensity values: slope=–3.22, intercept=–6.54), and although it is significantly different from 0 (t=5.01, d.f.=35, P<0.001) it explains little of the variance (r²=0.41). The broken line is a regression of only the maximal flight lengths at each intensity (denoted by open triangles), where the range of intensities was divided into 8 half log unit bins. The variance of this upper edge of data is explained well by linear regression (slope=–4.57, intercept=–7.69, r²=0.97) and is statistically significant (t=14.97, d.f.=6, P<0.001).