Data for: Strong phenotypic trait correlations between mating partners do not result from assortative mating in wild great tits (Parus major)

There is considerable debate about the occurrence of assortative mating
between phenotypic traits measured within natural populations.
Meta-analyses have implied that assortative mating occurs generally in
natural populations but recent work indicates these conclusions largely
result from biased data. Specifically, estimates of phenotypic
correlations between mating partners do not solely result from non-random
associations between individual-level traits of partners but also from
other biological processes (joint phenotypic plasticity, indirect genetic
effects), methodological practices (observer bias), and other unexplained
residual correlations (e.g. correlated measurement error). This paper puts
this critique to test. First, we estimated the overall phenotypic
correlation between phenotypic traits of mating partners for a wild
population of great tits. Second, we estimated various key variance
components to reveal the extent to which phenotypic correlations between
partners resulted from assortative mating, reversible plasticity, social
partner effects, and methodological practices. We performed our analyses
for a range of phenotypic traits (body mass, breathing rate, exploration
behaviour, wing and tarsus length) to derive general conclusions not
hinging on the specifics of the traits involved. Our analyses support the
conclusion that patterns of assortative mating exist at first glance but
occur because of the biasing effects of correlated residuals likely caused
by a combination of phenotypic responses to unknown environmental factors
or measurement error – not because of intrinsic patterns of assortative
mating.