Data from: A longitudinal analysis of the growth rate and mass of tail feathers in a great tit population: ontogeny, genetic effects and relationship between traits

Feathers have a diversity of functions in birds and are costly to produce,
so their growth rate and mass can be reliable indicators of nutritional
condition at the time of production. Despite the potential for feather
metrics to advance our understanding of foraging, they are underused in
avian ecology. One reason for this is the difficulty of interpreting
whether individual variation is driven by ontogenetic, genetic, or
environmental effects, which is exacerbated by the fact that most analyses
have been done on cross-sectional data. We addressed this deficit using a
longitudinal dataset of tail feathers collected from Great tits Parus
major to test for ontogenetic and genetic effects on growth rate, mass and
length, while controlling for body/feather size differences and other
confounding factors. First, we found that the type of moult episode and
experimentally-induced replacement differentially affected the length,
mass and growth of feathers, providing evidence of an ontogenetic effect
that should be considered when comparing these feather traits across
individuals as a measure of condition. Second, we detected moderate to
high repeatability and heritability values from parent-offspring
regression for these three feather traits, which are suggestive of an
underlying genetic component of variation. Third, we used a mean centring
within-individual approach to test whether feather growth rate and feather
mass (length-corrected) are indeed positively correlated with each other
as overlapping indicators of body condition in birds, and found that this
association, although positive, is weak and only significant between
individuals. This suggests that both metrics are not so intimately linked
as originally thought, and probably have different sensitivities to
variation in foraging performance and ecological conditions. Together with
the higher plasticity of feather growth rate compared to feather mass, our
results support the idea that feather growth rate is better suited for
examining short-term responses to environmental variation.