Seabirds constitute a key group of marine top-predators. While foraging seabirds prey mostly on schooling pelagic fish, crustaceans and squids. Because seabirds distribute over a wide spatial range they are sensitive to physical and biotic changes at several temporal scales. In the last 20 years bio-logging science has revolutionized our knowledge of how seabirds can act as monitors of prey stocks. One of the most interesting applications of data loggers on seabirds is determination of the distribution and availability of prey on which we have little knowledge such as mesopelagic fish, squid, and krill. There are now known to be several variables measurable by data loggers which estimate the number of prey caught by free-ranging seabirds. Such data loggers, in combined deployment on seabirds with time-depth or movement loggers (which record acceleration in one or more dimensions) provide data sets representing dependable indices of prey availability. While knowledge of seabird behaviour continues to improve, we still know little about the relationships between seabird behaviour and prey density/availability. Unravelling these relationships is a key step to calibrating the proxies of prey availability recorded by data loggers. Continuing to develop the use of instrumented seabirds as bio-indicators of marine resources is important in the quest to understand marine ecosystems and the conservation of top-predators
