Seabirds are considered excellent indicators of the state of the marine environment and are used throughout the world to provide signals from the marine environment.
Individuals of some species can live for 30 or more years, and by monitoring populations over time, signals on food availability and changes in the physical environment can be obtained. Population monitoring of key seabird species is also a management action identified by national conservation plans.
The locations of breeding sites and breeding populations of many species of seabirds have been recorded since the first modern visit to Heard Island in 1947. Long-term studies have made use of historical scientific records and early photographs, and aerial photographs have also been used to identify population sizes and trends in specific breeding populations since the 1940s. The most recent field work was undertaken in 2000/01 and 2003/04, involving populations counts and mapping using the global positioning system (GPS).
Observations indicate that the locations of some nests and colonies have changed with time as some breeding populations have increased or decreased. Some species are now nesting in areas that were until recently covered by glaciers, and that retreat of the glaciers over the past 40 years has facilitated the expansion of nesting by some species, such as king penguins.
There is evidence that some species, such as king penguins and black-browed albatross are increasing in number. There is a chance that populations of other species, such as macaroni, rockhopper and gentoo penguins may be decreasing, but there is uncertainty surrounding the rates and extent of decreases. Any such changes would reflect decreases reported on other subantarctic islands where in some cases, such as for rockhopper penguins, climate warming has been implicated in the decreasing population.
Parallel studies are investigating the diets and foraging behaviours of selected seabird species.