Correspondence

doi:10.1111/j.1469-7998.2006.00090.x Life-history theory predicts that adults of long-lived species such as seabirds should optimally balance investment in current and future offspring. However, when trying to optimize investment in offspring provisioning, the most energeti-cally costly component of seabird parental care, adults need to contend with large interannual fluctuations in prey availability and hence the cost of chick provision-ing. Adults faced with this uncertainty can mechanistically balance parental care by adopting a strategy somewhere along the continuum between maintaining constant investment in foraging effort between years and letting chick provisioning fluctuate or holding chick provisioning constant and varying investment in foraging effort. Using ship-based hydroacoustic assessment of prey, time-depth recorders attached to penguins and land-based observations at the breeding colony, we examined how foraging and reproductive effort in breeding chinstrap penguins Pygoscelis antarctica responded to interannual variation in the abun