This document summarizes three studies that examine how extra-pair paternity increases variance in male reproductive success across different bird species. A study of mountain bluebirds found high rates of extra-pair copulation and paternity increased male reproductive success. In little auks, most extra-pair copulations were unsuccessful at fertilization despite being common. Zebra finches showed extremely low extra-pair paternity in the wild but high rates in captivity. Overall, extra-pair paternity increased variance in reproductive success for male mountain bluebirds, little auks engage in many unsuccessful extra-pair copulations, and rates differ between wild and captive zebra finches.