Tracking the emperor penguin
across the pack ice

During the polar night on the coasts of Antarctica, the air temperature falls to minus 50°C, and the wind can reach over 250 km/h. The chill factor is increased by blizzards. In thick blizzards and average wind speeds of 125 km/h, ten metric tons of snow per hour blow through a square meter perpendicular to the wind. And yet in this hostile environment one creature lives and breeds-the emperor penguin. This bird not only faces more intense cold than any other on Earth, but also survives incredibly long periods without food. The time the penguins need to spend on the pack ice for breeding keeps them far from the sea, their only source of food. The male penguin, which incubates the couple's single egg alone, goes for four months without food in mid-winter.

How the emperor penguin has adapted to survive so long without food has gradually been revealed. However, these penguins do not defend territory, thus greatly reducing their energy outlay since they can maintain body temperature socially. By huddling together ten to a square meter, emperor penguins cut their energy outlay to a minimum.

However, it remained a mystery how the birds coped with the long trip to the open sea. After four months without food, male penguins in Adélie Land may be more than 200 km from the open sea when they leave their colony on the stable pack ice between the islands and the Antarctic mainland. Treadmill tests of energy expenditure have shown that the penguins store enough for no more than about 180 km.

The Argos system has helped us discover how emperor penguins move across the pack ice and through drifting floes. By overlaying the tracks of males carrying Toyocom transmitters on satellite imagery of the winter pack ice, we have shown that after their long winter fast, the penguins feed in ice-free stretches of water, called polynyas, some 110­130 km from the colony (fig. 1). The penguins take about twelve days to reach these ice-free areas, traveling day and night. They do stop occasionally, but only at night. It may well be that they find cracks or crevasses in the pack ice where they can feed.

Fig. 1 - Argos tracks of four foraging male emperor penguins (1-4) after their long winter fast. Circles indicate stops. The transmitters continued to operate at air temperatures of -30°C, well below the design specifications. From Ancel et al., Nature: 336-38, 1992.

Winter polynyas in the Antarctic have aroused great scientific interest, but are among the most inaccessible areas on Earth. It was thought that unmanned rovers would be the only way of studying them. An alternative method is to fit penguins with satellite tags.

Some months after this first success in tracking emperor penguins by satellite, a team led by G. Kooyman from the Scripps Institution of Oceanography, San Diego (U.S.) studied emperor penguins from the Cape Washington colony at the start of the southern summer. These birds swim out to sea, sometimes in loose packs, for food they store in their stomachs and regurgitate later for their young. The study showed that the round trip on these foraging expeditions can be up to 1500 km. Dive recorders interfaced to the Toyocom and Telonics transmitters showed that the penguins go down as far as 500 m (fig. 2). This means they scan considerable volumes of sea water for food.

The Argos system has helped us to clear up much of the mystery surrounding the movements of emperor penguins on the pack ice and at sea. Argos location and data acquisition equipment, with the right sensors, improves our understanding of the penguins' food strategy, making them into valuable assistants for exploring some of the most inaccessible environments on Earth. They can give us fundamental information about those environments, and indicate changes in marine resources in the Antarctic Ocean. These changes are important, because we believe that the fragile Antarctic ecosystems will give early notice of major global changes.

Do emperor penguins always feed in the same sea areas, which assumes that the polynyas are fairly stable, or do these areas depend upon ice conditions? How does their "food strategy" vary as a function of available marine resources? These are just two of the unanswered questions. Fascinating prospects are opening up as new equipment and techniques are developed in fruitful cooperation between manufacturers and users.