Data from: Unscrambling variation in avian eggshell colour and patterning in a continent-wide study

The evolutionary drivers underlying marked variation in the pigmentation
of eggs within many avian species remains unclear. The leading hypotheses
proposed to explain such variation advocate the roles of genetic
differences, signalling and/or structural integrity. One means of testing
amongst these hypotheses is to capitalise on museum collections of eggs
obtained throughout a broad geographic range of a species to ensure
sufficient variation in predictors pertaining to each hypothesis. Here we
measured colouration and patterning in eggs from 271 clutches of
Australian Magpies (Cracticus tibicen) collected across most of their
geographic range of ca. 7 million km2; encompassing eight subspecies,
variation in environmental parameters, and the presence/ absence of a
brood parasite. We found considerable variation in background colour, as
well as in the extent and distribution of patterning across eggs. There
was little evidence that this variation was explained by subspecies.
However, we found marked differences in relation to the contemporary
presence of a brood parasite. Measures of maximum temperature, relative
humidity, leaf area index and soil calcium all contributed to variation in
egg appearance, although their explanatory power was relatively low. Our
results suggest that multiple factors combine to influence egg appearance
in this species, and that even in species with highly variable eggs,
colouration is not readily explained.   Note: An error in data
manipulation was identified and corrected. A correction has been applied
to this article (April 2024), approved by RSOS.