Data from: 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 (~5,000) were based on family
level egg mass-body mass regressions, with the remainder derived from
other relationships such as ordinal regressions.  We compared
estimating regressions based on adult vs. female body masses, and after
finding little difference between the two based our final estimates on
adult masses as those were more numerous in the literature.  What
small differences between adult- and female-based regressions that did
occur were not related to sexual size dimorphism across
families.  These new estimates, coupled with ~5,000 egg masses
reported in the literature, provide a foundation of over 10,000 species
for wider investigations assessing variation in reproductive effort in
birds over a broad array of ecological and evolutionary
contexts.