Seabirds eat primarily fish, squid, and small crustaceans like krill, though the exact mix varies enormously depending on the species, location, and time of year. Some seabirds are specialist hunters that dive deep for a single type of prey. Others are opportunistic scavengers that will eat almost anything they find on or near the ocean surface, including jellyfish, worms, insects, and scraps thrown overboard from fishing boats.
Fish: The Core of Most Seabird Diets
Fish are the single most important food source for seabirds worldwide. Energy-rich, oily species are especially prized. Herring, sprat, capelin, sandeels, anchovies, and mackerel all rank among the most commonly eaten fish across seabird families. These species are high in fat, which makes them efficient fuel for birds that burn enormous amounts of energy flying over open ocean.
Seabirds are often selective about exactly which fish they catch. Common guillemots feeding chicks at breeding colonies were found to bring back almost exclusively ripe female capelin, ignoring males and spent females. The reason is straightforward: egg-laden females carry more energy per fish. During breeding season, many seabird species switch to whatever prey is locally abundant and calorie-dense, often targeting fish that enter coastal waters to spawn. Little penguins in Australia, for example, shift to eating anchovies and sprat that move inshore during spring and summer spawning runs.
Squid and Other Cephalopods
Squid are a major food source for many open-ocean seabirds, especially albatrosses and petrels. Grey-headed albatrosses get roughly 50% of their diet by weight from squid, with the remainder split between fish and krill. Their close relatives, black-browed albatrosses, eat less squid and rely more heavily on krill (about 40% of their diet), though both species eat similar types of prey overall.
Because squid bodies are soft and digest quickly, scientists studying seabird diets often find only the hard, indigestible beaks left behind in a bird’s stomach. These beaks can persist in the gut for a month or longer, which means squid consumption is easy to confirm but tricky to quantify precisely.
Krill and Other Crustaceans
In polar and subpolar waters, tiny shrimp-like crustaceans called krill form the foundation of many seabird diets. Adélie penguin chicks in some Antarctic colonies get roughly two-thirds of their food from Antarctic krill. At other colonies just a few hundred kilometers away, the same species may eat mostly fish instead, with krill dropping to as little as 11% of the diet. Location and local prey availability drive these differences more than any innate preference.
Emperor penguin chicks, by contrast, lean heavily toward fish regardless of location. Antarctic silverfish made up about 74% of their diet at two separate breeding sites in the Ross Sea. Krill and squid filled in the rest. Farther from the poles, seabirds eat a wider range of crustaceans including crabs and other decapods, though these tend to be a smaller part of the diet compared with fish.
Nocturnal Hunters and Surface Feeders
Not all seabirds hunt during the day. Storm-petrels, among the smallest seabirds, are highly active at night. Leach’s storm-petrels are the most nocturnally active burrowing seabird in the North Atlantic, and researchers believe they may track bioluminescent prey glowing near the ocean surface. This is one reason these birds are so frequently disoriented by artificial lights on ships and coastal structures: they may mistake the glow for food.
Surface feeders like storm-petrels, shearwaters, and many gull species pick prey from the top few centimeters of water or pluck floating organisms while in flight. Their diets tend to include a broader mix of small fish, squid, floating crustaceans, and even polychaete worms and jellyfish. Diving species like puffins, murres, and penguins can reach deeper prey and tend to specialize on schooling fish.
How Fishing Boats Change Seabird Diets
Commercial fishing has reshaped how many seabirds eat. Scavenging species, particularly gulls, fulmars, and some albatrosses and petrels, have learned to follow trawlers and feed on the fish and invertebrates thrown overboard as bycatch. This easy food source fundamentally alters their behavior. When trawlers are operating, Mediterranean seabirds stick to predictable foraging routes with short travel distances, essentially commuting to a reliable food source. When trawlers stop operating (on weekends or during fishing bans), those same birds shift to covering much larger, more unpredictable distances as they search for natural prey.
This dependence on discards is a double-edged sword. While it provides easy calories, it ties seabird populations to the fishing industry. Policy changes that reduce discards, which are being implemented in several regions, could force sudden dietary shifts for species that have come to rely on them.
Warming Oceans and Shifting Prey
Rising ocean temperatures are rearranging when and where seabird prey is available. In the North Sea and Northeast Atlantic, populations of zooplankton and phytoplankton, the tiny organisms at the base of the food chain, have been declining over the past half-century. This decline ripples upward to affect the small fish that seabirds depend on.
The changes are not as simple as prey moving northward to cooler water. Krill populations, for instance, are experiencing what scientists describe as a “habitat squeeze,” condensing into shrinking pockets of cold water rather than shifting in an orderly way toward the poles. In other regions, fish that seabirds rely on are arriving at traditional feeding grounds later in the season as warming water disrupts their migration timing. When prey arrival falls out of sync with the seabird breeding season, chicks may go hungry during the critical weeks when they need the most food.
The Plastic Problem
About 35% of seabirds have ingested plastic, a rate higher than marine mammals (12%) but lower than sea turtles (47%). Hard plastic fragments are by far the most common type found in seabird stomachs, showing up in about 32% of individuals studied. Soft plastics, fishing debris, rubber, and foam each appear in smaller percentages. An estimated 1.6% of seabirds die as a direct result of plastic ingestion, through intestinal blockage, internal injury, or the false sense of fullness that prevents them from eating enough real food.
Why Seabird Diets Matter Beyond the Birds
Seabirds do not just take from the ocean. They transport enormous quantities of nutrients from sea to land. Globally, seabird colonies deposit an estimated 591,000 metric tons of nitrogen and 99,000 metric tons of phosphorus per year through their droppings. Both nutrients are critical for plant growth and aquatic productivity. The Antarctic and Southern Ocean coasts receive the largest share of this input. A significant portion of the excreted nitrogen and phosphorus dissolves readily in water, fertilizing coastal ecosystems and, in some cases, enriching soil on nesting islands enough to support plant communities that would not otherwise exist. What seabirds eat at sea quite literally shapes the landscapes where they come ashore.