Eggshell coloration is an indicator of dietary calcium in Common Pheasants (<i>Phasianus colchicus</i>)

According to the structural‐function hypothesis, eggshell pigment protoporphyrin, deposited at weak spots, can strengthen shell structure when calcium is lacking in avian species. However, this hypothesis has not been tested species that produce pigmented eggs of uniform ground colour without spotting patterns. We using 435 produced on seven diets (0.2–4.5%) given Common Pheasants Phasianus colchicus , a produces large number low‐calcium diet with unspotted eggshells composed mainly protoporphyrin. found pheasants lowest (0.2%), which had thinner eggshells, containing more protoporphyrin‐based coloration than four six other diets, suggesting employs pigmentation as available low. Our results provide first, least partial support for structural function pigments producing often calcium‐limited. This pattern may be widespread ground‐nesting taxa also numbers and are potentially limited by during breeding.