Data and R code supporting the article Seasonal variation in eggshell calcium and trace elements reveals shifting constraints on resource allocation in an urban passerine

The dataset contains records for 167 European Blackbird (Turdus merula) eggshells collected between 2006 and 2017 in Stefan Żeromski Park, Szczecin, Poland. It includes measured concentrations of calcium (Ca), strontium (Sr) and lead (Pb), expressed in ppm dry weight, together with information on breeding timing and clutch order, egg fate, embryonic development, female age and tarsus length, female lifespan and lifetime reproductive success, and precipitation conditions. The dataset enables analyses of variation in eggshell elemental composition in relation to female characteristics, breeding phenology and environmental conditions. Accompanying R code reproduces the statistical analyses and figures presented in the associated publication.