Variation in capercaillie egg size, pigmentation, and eggshell thickness.

There was found great variation in birds' eggs, depending factors like life history, genetics or environment. While interspecies variation is well known, interspecies variation is much less described. Aim of conducted studies was to describe egg size, eggshell pigmentation and thickness in relation to female factor, season and laying order. Unhatched eggs and post-hatched eggshells were collected for three years from two breeding centers in Wisła Forestry District and Leżajsk Forestry District. Date of laying and mother id were noted. From 51 females, 312 eggshells were obtained in total. This includes 171 post-hatched eggshells and 141 eggs infertile or containing embryos up to the 4th day of development. Eggs were measured (maximum length and width) with the use of electronic caliper. The egg shape index, i.e. the ratio of long to short axis, was calculated. Eggshell pigmentation intensity (lightness) was assessed with portable colorimeter NH310. After removing eggshell membranes, eggshell thickness was measured to the nearest 0.001 mm using a micrometer with a 0.2-mm spline diameter. In the majority of cases, no statistically significant correlation was found between the female id and laying order, eggshell thickness, pigmentation, measures and egg shape. There was no individual variability of the pigmentation of the eggshells in subsequent seasons. We did not found significant differences in eggshell thickness, measures or shape between breeding centers, but eggshells from Leżajsk were lighter. Coefficient of variation showed that females lay similar eggs in clutch in size (CV = 0,041 for length and 0.014 for width), shape (CV = 0.039) and pigmentation (CV = 0,036). The most variable was eggshell thickness (CV = 0.053). Conclusions: Females lay similar clutches through subsequent breeding seasons. As expected, the greatest variation was found in eggshell thickness, because this egg trait depends very much on external factors, like bird diet, physiological limitations, and environmental conditions. [ABSTRACT FROM AUTHOR]