Macaroni penguins are the most numerous penguin species but have declined dramatically as climate change alters krill distribution and abundance in their Antarctic and sub-Antarctic foraging habitat.
Macaroni penguin chick starvation during krill shortage periods causes measurable individual welfare impacts at enormous scale. Chicks that receive insufficient krill from foraging parents grow slowly, lose condition, and die from exposure and starvation over days in their exposed nest sites. Adults returning from extended, unsuccessful foraging trips have depleted body reserves and may face difficulty completing their own moult, a critical process for waterproofing feathers. The energetic demands of macaroni penguins at breeding colonies are extraordinary; adults swim hundreds of kilometres and dive repeatedly to 100m depth to provision their chick. When prey is unavailable within this foraging envelope, both individual welfare and breeding success collapse. The scale of macaroni penguin numbers means that population-level welfare impacts involve millions of individuals experiencing nutritional stress simultaneously.