Experimentally impaired female condition does not affect biliverdin-based egg colour

It has been proposed that blue-green egg coloration is a
condition-dependent female sexual trait that may modify paternal care in a
post-mating sexual selection scenario. This pattern may arise because the
pigment responsible for eggshell colouration (biliverdin) may be a costly
and limited resource, whose availability is linked to female health state.
Thus, it can be predicted that females whose condition is compromised
should be constrained in their capacity to deposit biliverdin in the
eggshell, thus producing paler clutches. To test this hypothesis, we
performed a handicapping experiment by clipping some feathers of female
spotless starlings before egg laying and measuring the colour of their
clutches. We expected the handicapping treatment to increase flying costs,
impairing female overall condition and resulting in paler clutches. Our
experiment was successful in lowering the weight gain of handicapped with
respect to control females. However, in contrast to our expectations, we
found no effect of the treatment on eggshell colouration. Eggshell colour
varied along the laying order, with initial eggs of the laying sequence
being relatively paler than the rest of the clutch, but this pattern was
not different between experimental groups. Despite a very similar
methodology, our results differ from a previous study and offers no
support to the post mating sexual selected hypothesis, questioning the
general applicability of the sexual selection role of eggshell coloration.