penguins are not as harmless as they look. Recent research in Antarctica has revealed that they steal each other's eggs and may even peck each other to death to guard their territory at remote, windswept nesting sites.

The aggressive behaviour of male penguins at nesting sites has been linked to high levels of testosterone in their blood during early mating season. Researchers believe their hormonal secretions are regulated by natural selection, which enables their offspring to survive in a harsh environment.

"The thing that most impresses me about the penguins is how attached they are to their young and to their nesting sites,' says Carol Vleck, a zoologist at Iowa State University, us. Vleck observed sudden shifts in penguins' behaviour from aggression to raising and nurturing as soon as the chicks hatch. During breeding season, male penguins keep the eggs warm and guard them from skuas, which are hawk-like birds that terrorise nesting sites, while the females go to the sea to feed.