Estimating egg mass-body mass relationships in birds

The mass of a bird’s egg is a critical attribute of the species’ life history and represents a fundamental component of reproductive effort.  Indeed, the trade-off between the number of eggs in a clutch and clutch mass lies at the heart of understanding how environmental attributes such as nest predation or adult mortality influence reproductive investment.  However, egg masses have not been reported for the majority of avian species.  We capitalized on the strong allometric relationship between avian body mass and egg mass to produce egg mass estimates for over 5,500 species previously lacking such information.  These estimates are accompanied by measures of the robustness of the regressions used to produce them (e.g., sample size, root mean square error of estimation, coefficient of determination, degree of extrapolation), thus allowing independent evaluation of the suitability of any estimate to address a particular research question relating to avian life history.  Most estimates (~...