Summary
The determination of the conservation status for a species at risk of extinction is based largely upon consistent change in the population size. In long-lived species, such as seabirds, longterm monitoring is required to establish the extent of the natural variability in a population and to detect true change. As studies spanning several generations within the same population are rare, researchers may turn to historically collected census information to expand the time frame of their studies. While in principle a valid approach, several limitations need to be considered to use historical information appropriately. Census information, collated from the 1950s to the present, of 3 populations of southern giant petrels Macronectus giganteus in the Australian Antarctic Territory (AAT) is used to highlight potential limitations inherent in historical data. We demonstrate the importance of census time and count units when investigating potential changes in populations. Published accounts indicate that the numbers of southern giant petrels in the AAT have decreased significantly since their discovery and that more recently some recovery has taken place. However, for 2 of the 3 populations we could not find evidence supporting a change.