GREY SEAL MALES - ENERGETIC AND BEHAVIORAL LINKS BETWEEN SIZE AND SEXUAL SUCCESS

The costs of breeding in male grey seals (Halichoerus grypus) have been estimated by repeated weighings of animals on the breeding grounds. Individual variations in male size and rate of weight loss were positively correlated with measures of sexual behaviour. Grey seal males did not form a linear dominance hierarchy, nor were they of equal status, but large males lost few encounters. Finite resources set a limit on the time that can be spent ashore being sexually active. These limits can be predicted using the collected data on size and energy use, and the results emphasize the significance of large size in relation to breeding success in grey seal males. The largest males may on average sire 10 times as many offspring as the smallest breeding males.