Southern rockhopper penguins have declined by up to 90% on some sub-Antarctic islands over 50 years from oceanographic changes affecting their prey.
Rockhopper chicks dying from starvation in poor prey years experience prolonged hunger and weakness before death. Adult birds in poor nutritional condition are more vulnerable during the energetically demanding moult period when they cannot feed. Falls from steep nesting cliffs cause injury and death in adults weakened by nutritional stress. The dramatic population collapse on Falkland Islands means individual welfare harms have occurred at massive scale over decades. Understanding the causes of prey depletion is essential for addressing the welfare-relevant population crisis.