FIGURE 4.

Eggshell thickness at the egg equator as a function of egg length and egg width within and among 12 avian species during 2014–2018. (a) Individual eggs’ equator eggshell thicknesses as a function of egg length within each species (slopes for each species from individual species regressions). (b) Individual eggs’ equator eggshell thicknesses as a function of egg width within each species (slopes for each species from individual species regressions). (c) Arithmetic mean (± SD) eggshell thicknesses and egg lengths (raw data) are shown for each species on top of the among‐species regression (equator eggshell thickness [mm] = (0.00664 × egg length [mm]) – 0.06082) based on the species’ mean values. (d) Arithmetic mean (± SD) eggshell thicknesses and egg widths (raw data) are shown for each species on top of the among‐species regression (equator eggshell thickness [mm] = (0.00999 × egg width [mm]) – 0.07884) based on the species’ mean values