The males of Snares Cape Pigeons (Daption capense australe) breeding at the Snares Islands are larger than females, especially in head plus bill length, mid-toe plus claw, bill length, bill depth, tarsus, and weight. By using the measurements head plus bill length and mid-toe plus claw, one can reliably sex about 82% of the Snares Islands birds. The amount of sexual dimorphism is similar in both races of cape pigeon. The importance of having a wide range of calls during breeding is favoured as the reason for dimorphism having developed in fulmarine petrels.