Quantifying the maculation of avian eggs using eggshell geometry

Abstract

Birds’ eggs often exhibit considerable variation in the presence and pattern of superficial pigmentation, or maculation. However, despite long appreciation of the nature of this variation both between and within species, there is still poor understanding of why such a diversity of patterns has evolved. Accurately quantifying eggshell maculation is therefore key to elucidating its functional significance. Maculation is typically quantified from photographs, and so measurements may be biased by the perceived distortion introduced by the curvature of the eggshell. Here, I consider egg geometry in order to derive measures of curved distance and surface area that can be used to characterize eggshell maculation patterns more accurately, and demonstrate the utility of this approach for quantifying and visualizing eggshell maculation from standard photographs.