Figure 2.
(a) Avian eggshell surface roughness (Sa nm) of non-parasitic species (left, blue) and brood-parasitic species (right, red). (b) Avian eggshell surface wettability (CA), as measured by the mean CA of a water droplet on eggshell surfaces of non-parasitic species (left, blue) and brood-parasitic species (right, red). The red dotted line at 90° is the threshold between hydrophilic (less than 90°) and hydrophobic (greater than or equal to 90°) eggshell surfaces. No significant differences were evident between the eggs of brood-parasitic and non-parasitic eggs for either trait (Sa: t = 0.09, p = 0.26; CA: t = 0.59, p = 0.79). Boxplots show the interquartile range and median value as a line, with whiskers encompassing values within 1.5 times the interquartile value. The distribution of the data is shown in scatterplots (overlaid) and frequency plots (alongside each pairing). Each data point shows a measurement from one egg, and each egg is from a different nest; analyses take into account phylogenetic non-independence, as well as non-independence of multiple eggs per species (see Methods).