Data from: Better stay together: pair bond duration increases individual fitness independent of age-related variation

Prolonged pair bonds have the potential to improve reproductive
performance of socially monogamous animals by increasing pair familiarity
and enhancing coordination and cooperation between pair members. However,
this has proved very difficult to test robustly because of important
confounds such as age and reproductive experience. Here, we address
limitations of previous studies and provide a rigorous test of the mate
familiarity effect in the socially monogamous blue-footed booby, Sula
nebouxii, a long-lived marine bird with a high divorce rate. Taking
advantage of a natural disassociation between age and pair bond duration
in this species, and applying a novel analytical approach to a 24 year
database, we found that those pairs which have been together for longer
establish their clutches five weeks earlier in the season, hatch more of
their eggs and produce 35% more fledglings, regardless of age and
reproductive experience. Our results demonstrate that pair bond duration
increases individual fitness and further suggest that synergistic effects
between a male and female's behaviour are likely to be involved in
generating a mate familiarity effect. These findings help to explain the
age- and experience-independent benefits of remating and their role in
life-history evolution.