Data from: Great spotted cuckoo eggshell microstructure characteristics can make eggs stronger

Obligate avian brood parasites lay stronger eggs than their hosts or
non-parasitic relatives because they are rounder and have a thicker
eggshell. Additionally, some other characteristics of the brood parasitic
eggshells related to their microstructure such as size and orientation of
calcite crystal units could also contribute to generating even stronger
shells. An eggshell microstructure formed by small randomly oriented
calcite crystal units can increase the robustness of the eggshells of
birds. Here, the eggshell microstructure of avian brood parasites as well
as their hosts have been characterized in detail, using X-ray diffraction
analyses to estimate the size and degree of orientation of calcite crystal
units making the eggshell. Specifically, the brood parasitic great spotted
cuckoo (Clamator glandarius) and two hosts (jackdaws, Corvus monedula and
magpie, Pica pica) and one non-host species (the pigeon, Columba livia
domestica) were considered. Calcite crystal of the eggshell of the brood
parasitic species was smaller and more randomly oriented than those of the
eggshells of non-parasitic species, which suggest that eggshell
microstructure would contribute to explain why parasitic eggs are more
resistant to breakage than those of their hosts.