Data from: Correlates of complete brood failure in blue tits: could extra-pair mating provide unexplored benefits to females?

Behavioural ecologists have for decades investigated the adaptive value of
extra-pair copulation (EPC) for females of socially monogamous species.
Despite extensive effort testing for genetic benefits, there now seems to
be a consensus that the so-called ‘good genes’ effects are at most weak.
In parallel the search for direct benefits has mostly focused on the
period surrounding egg laying, thus neglecting potential correlates of EPC
that might be expressed at later stages in the breeding cycle. Here we
used Bayesian methods to analyse data collected over four years in a
population of blue tits (Cyanistes caeruleus), where no support was
previously found for ‘good genes’ effects. We found that broods with mixed
paternity experienced less brood failure at the nestling stage than broods
with single paternity, and that females having experienced complete brood
failure in their previous breeding attempt had higher rates of mixed
paternity than either yearling or previously successful females. To better
understand these observations we also explored relationships between
extra-pair mating, male and female phenotype, and local breeding density.
We found that in almost all cases the sires of extra-pair offspring were
close neighbours, and that within those close neighbourhoods extra-pair
sires were older than other males not siring extra-pair offspring. Also,
females did not display consistent EPC status across years. Taken together
our results suggest that multiple mating might be a flexible female
behaviour influenced by previous breeding experience, and motivate further
experimental tests of causal links between extra-pair copulation and
predation.