Data from: The correlation between colouration and exploration behaviour varies across hierarchical levels in a wild passerine bird

IIn vertebrates, darker individuals are often found to be more active and
willing to take risks (representing characteristics of a ‘proactive’
coping style), whereas lighter individuals are instead more cautious and
less active (representing characteristics of a ‘reactive’ coping style).
It is thus generally expected that melanin-based colouration and
proactivity form a suite of positively integrated traits at the
among-individual level. Here we use a multi-generational pedigree of
free-living great tits (Parus major) to partition variation in, and the
correlation between, melanin-based breast stripe (‘tie’) size and
exploration behaviour (a proxy for coping style) into its among- and
within-individual components. We show that both traits harbour heritable
variation. Against predictions, tie size and speed of exploration were
negatively correlated at the among-individual level due to the combined
influences of permanent environmental and additive genetic effects. By
contrast, the two traits were weakly positively correlated within
individuals (i.e., individuals increasing in tie size after moult tended
to become more explorative). The patterns of among-individual covariance
were not caused by correlational selection as we found additive and
opposite selection pressures acting on the two traits. These findings
imply that testing hypotheses regarding the existence of a ‘syndrome’ at
the among-individual level strictly requires variance partitioning to
avoid inappropriate interpretations as the negative ‘unpartitioned’
phenotypic correlation between exploration and tie size resulted from
counteracting effects of within- and among-individual correlations.
Identifying sources and levels of (co)variation in phenotypic traits is
thus critical to our understanding of biological patterns and evolutionary
processes.