Scientific American Struggling Seabirds Are Red Flag for Ocean Health These sentinels of marine ecosystems point to the damage climate change, overfishing and other human pressures are causing Advertisement Seabirds are “sentinels” of ocean health. If marine ecosystems are suffering, the birds will be among the first to show it. Now a major study finds that seabirds in the Northern Hemisphere are already struggling. And without extra precautions, those in the Southern Hemisphere might be next. The findings point to broader patterns of environmental change across the world’s oceans. Climate change, combined with pollution, overfishing and other human activities, is steadily altering marine food webs. Food sources are shifting. Some fish populations are dwindling or migrating to new areas.