Appendix S1 - Testosterone, Plumage Colouration and Extra-Pair Paternity in Male North-American Barn Swallows

Relationships between phenotype (testosterone concentration and length of the longest tail feather) and fertilization success of male barn swallows calculated from first nests only (most pairs were double brooded). Fertilization success was split into i) cuckoldry rate, i.e. the proportion of extra-pair young in a male's own first brood, ii) extra-pair fertilization success in first nests (EPF), and iii) total fertilization success, i.e. the total number of offspring produced in first nests. Extra-pair fertilization success was analyzed in two steps; first using a binomial error distribution, and second using a normal error distribution, including only those males that gained extra-pair young (see Methods for rationale). (DOC)