breed.data.dryad.useThis file contains data required for the simulation that quantifies the consequences of observation failure due to offspring mortality for estimates of inbreeding avoidance through extra-pair reproduction.data.epy.dryad.useThis file contains the data for the basic analysis of inbreeding avoidance through extra-pair reproduction.data.fems.dryad.useThis file contains the data for the analyses of extra-pair reproduction, clutch size, probability of offspring mortality and brood size in relation to a female's kinship with her socially paired male.data.neighbours.dryad.useThis dataset describes the coefficient of kinship between each focal female and her first-, second- and non-neighbour males.neighbours.na.dryad.useThis file contains data required for the simulation that quantifies the consequences of observation failure due to offspring mortality for estimates of inbreeding avoidance through extra-pair reproduction.neighbours1.dryad.useThis file contains data required for the simulation that quantifies the consequences of observation failure due to offspring mortality for estimates of inbreeding avoidance through extra-pair reproduction.neighbours2.dryad.useThis file contains data required for the simulation that quantifies the consequences of observation failure due to offspring mortality for estimates of inbreeding avoidance through extra-pair reproduction.ped.data.dryad.useThis file contains data required for the simulation that quantifies the consequences of observation failure due to offspring mortality for estimates of inbreeding avoidance through extra-pair reproduction.simulationRcode.dryad.useThis simulation code quantifies the consequences of observation failure (ie pre-banding mortality) for estimates of the pattern of occurrence of extra-pair reproduction in relation to the kinship between a female and her socially-paired male, and the degree of inbreeding avoidance through extra-pair reproduction.

Extra-pair reproduction is widely hypothesised to allow females to avoid inbreeding with related socially-paired males. Consequently, numerous field studies have tested the key predictions that extra-pair offspring are less inbred than females’ alternative within-pair offspring, and that the probability of extra-pair reproduction increases with a female's relatedness to her socially-paired male. However such studies rarely measure inbreeding or relatedness sufficiently precisely to detect subtle effects, or consider biases stemming from failure to observe inbred offspring that die during early development. Analyses of multi-generational song sparrow (Melospiza melodia) pedigree data showed that most females had opportunity to increase or decrease the coefficient of inbreeding of their offspring through extra-pair reproduction with neighbouring males. In practice, observed extra-pair offspring had lower inbreeding coefficients than females’ within-pair offspring on average, while the probability of extra-pair reproduction increased substantially with the coefficient of kinship between a female and her socially-paired male. However, simulations showed that such effects could simply reflect bias stemming from inbreeding depression in early offspring survival. The null hypothesis that extra-pair reproduction is random with respect to kinship therefore cannot be definitively rejected in song sparrows, and existing general evidence that females avoid inbreeding through extra-pair reproduction requires re-evaluation given such biases.