Capercaillie (Tetrao urogallus) eggshell pigmentation, maculation and thickness

Abstract

Eggshells properties (mainly thickness, pigmentation and shape) vary within avian taxa across species, and intraspecifically with age, environmental conditions or individual features of the animals. The properties and appearance of eggshells are important for successful breeding both for birds kept in captivity and in breeding centres and those living in their natural environment. The presented study focuses on the association between the pigmentation, maculation and eggshell thickness of Western Capercaillie (Tetrao urogallus) kept in captivity. The eggs were collected during the entire egg-laying season in order to determine the factors which influence eggshell pigmentation and thickness across the laying period. We found that at the equator surface the lightest eggs had a tendency to be thinner than the darkest ones. In addition, eggshells with a smooth pattern were thinner at the equator, especially when compared to the mottled ones. There was no statistically significant association between the eggshell overall lightness (eggshell pigmentation except the concentrated pigment spots), maculation and eggshell thickness at the blunt and sharp ends of the eggshell. Eggshells were on average 5.5% thicker at spots than in other areas. The obtained results suggest that the spot pigment forms an additional layer on the Capercaillie eggshell and does not compensate for the loss of thickness, as observed in some bird species (Passeriformes, Falconiformes).