Data from: Assortative mating by colored ornaments in blue tits: space and time matter

Assortative mating is a potential outcome of sexual selection and
estimating its level is important to better understand local adaptation
and underlying trait evolution. However, assortative mating studies
frequently base their conclusions on small numbers of individuals sampled
over short periods of time and limited spatial scales even though
spatiotemporal variation is common. Here, we characterized assortative
mating patterns over 10 years in four populations of the blue tit
(Cyanistes caeruleus), a passerine bird. We focused on two plumage
ornaments—the blue crown and the yellow breast patch. Based on data for
1,657 pairs of birds, we found large interannual variation: assortative
mating varied from positive to negative. To determine whether there was
nonetheless a general trend in the data, we ran a within-study
meta-analysis. It revealed that assortative mating was moderately positive
for both ornaments. It also showed that mating patterns differed among
populations, and especially between two neighboring populations that
displayed phenotypic divergence. Our results therefore underscore that
long-term studies are needed to draw broad conclusions about mating
patterns in natural populations. They also call for studying the potential
role of assortative mating in local adaptation and evolution of ornaments
in both sexes in blue tits.