Data from: Indirect fitness benefits through extra-pair mating are large for an inbred minority, but cannot explain widespread infidelity among red-winged fairy wrens. Here, we present a comprehensive study which tests whether females gain indirect benefits from EPP in the cooperatively breeding red-winged fairy-wren (Malurus elegans). To compare performance of extra-pair and within-pair offspring, we use an integrated fitness measure that combines several fitness components: first year and adult survival, recruitment to a breeding position and reproductive success within the first three years of life. Such an integrated fitness measure accounts for the facts that some components of fitness are more important than others and that singling out specific life-stages may under- or overestimate the overall benefits of EPP on lifetime fitness. Data were collected for seven cohorts of offspring hatched during the 2008 to 2014 seasons which were monitored up to and including 2016 in Smithbrook Nature Reserve, Western Australia (34°20’S, 116°10’E). The main study area comprised ~65 territories in which > 99% of the adult birds were individually colour-banded. In this area each territory was checked at least fortnightly for group composition, survival and breeding activity throughout the breeding season (October-January). In addition, in another ~30 territories surrounding the main area 80% of the birds were colour-banded and nest searching was done opportunistically.

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