Data from: Egg size and offspring performance in the collared flycatcher (Ficedula albicollis): a within-clutch approach

Adaptive within-clutch allocation of resources by laying females is an
important focus of evolutionary studies. However, the critical assumption
of these studies, namely that within-clutch egg-size deviations affect
offspring performance, has been properly tested only rarely. In this
study, we investigated effects of within-clutch deviations in egg size on
nestling survival, weight, fledgling condition, structural size and
offspring recruitment to the breeding population in the collared
flycatcher (Ficedula albicollis). Besides egg-size effects, we also
followed effects of hatching asynchrony, laying sequence, offspring sex
and paternity. There was no influence of egg size on nestling survival,
tarsus length, condition or recruitment. Initially significant effect on
nestling mass disappeared as nestlings approached fledging. Thus, there
seems to be limited potential for a laying female to exploit within-clutch
egg-size variation adaptively in the collared flycatcher, which agrees
with the majority of earlier studies on other bird species. Instead, we
suggest that within-clutch egg-size variation originates from the effects
of proximate constraints on laying females. If true, adaptive explanations
for within-clutch patterns in egg size should be invoked with caution.