Individuals in species with long-term social monogamy often incur fitness costs after mate change. We evaluated the relative contributions of mate familiarity and male breeding experience to the costs of mate change of female black brant geese (Branta bernicla nigricans). We assessed the effects of mate change on relative nest initiation date, clutch size, brood size at hatch, growth rates of goslings, and prefledging survival of offspring. We modeled variation in relative nest initiation dates, clutch size, initial brood size, and gosling growth rates using generalized linear mixed models in Program R. We estimated prefledging survival with Cormack–Jolly–Seber models in Program MARK using reencounters of webtagged goslings. Mate change had a small effect on relative nest initiation date, clutch size, and initial brood size, but no effect on growth rates of brant goslings. Females breeding with an unfamiliar, but experienced male had goslings with higher prefledging survival rates (ϕ = 0.44±0.11 [95% confidence interval]) than those breeding with a familiar, experienced mate (ϕ = 0.30±0.04). However, females that changed mates and re-paired with an inexperienced male had goslings with substantially lower prefledging survival rates (ϕ = 0.20±0.04) than any other group of females. Our findings indicate that reproductive output by female brant is affected by male experience rather than mate familiarity. We believe that female brant typically benefit from mate retention because most will not acquire an experienced partner after mate change.