Figure 4.
Contact angle (θc) of a water droplet to eggshell surface plotted as a function of (a) adult body mass, (b) annual temperature, (c) eggshell maculation and (d) mode of development. Passerines (pink) and non-passerines (blue) were analysed separately, and each data point represents the mean θc for a given species. Linear regressions for each avian group are applied in (a) and (b). Within each avian group and across all birds, θc significantly decreased with larger body mass and increased with higher annual temperature. In the hybrid box plots (c,d), species θc are shown as filled circles, vertical line indicates the median, box shows the interquartile range (IQR) and the whiskers are 1.5 × IQR and their distribution are shown as histograms. Significant differences between categorical variables based on conditionally averaged models are given in asterisks with ***p < 0.001, **p < 0.01and *p < 0.05.