How skuas, frigatebirds, and gulls are helping spread avian influenza Premium

Food-stealing behaviour of the kleptoparasites such as skuas, frigatebirds, and gulls can enable the virus to spread.

It’s not easy finding food at sea. Seabirds often stay aloft, scanning the churning waters for elusive prey. Most seabirds take fish, squid, or other prey from the first few metres of seawater. Scavenging is common.

But there are other tactics. Frigatebirds, skuas, and gulls rely on the success of other seabirds. These large, strong birds chase, harry, and attack their targets until they regurgitate or drop the prey they’ve just caught. They’re the pirates of the seabird world, stealing hard-earned meals from other species. This behaviour is known as kleptoparasitism, from the Ancient Greek word kléptēs, thief.

The strategy is brutal, effective, and a core behaviour for these important seabirds. But as our new research shows, it comes with major risks for the thieves. The new strain of avian flu is killing birds by their millions – and we found kleptoparasitism could spread the virus very easily.

It’s not that frigatebirds, skuas, and gulls can’t hunt. They can and do catch their own food. But hunting fish and squid is hard work. It’s much easier to use extortion tactics to win the food from other seabirds.

These tactics have made these birds very successful as foragers. They hang around the breeding sites of birds such as gannets and terns waiting for a tired parent to return from the sea with a crop of food.

For the seabirds being targeted, these kleptoparasitic birds are just one more threat. The world’s 362 species of seabird can be found across every ocean and many islands. At sea, they prey on fish and squid. When they nest or rest on islands, their nutrient-rich guano shapes soil and plant communities, defining entire ecosystems.

But they are not doing well. Just under half of all seabird species (155) are now classified between “near threatened” and “critically endangered” on the world’s list of threatened species, the IUCN Red List. Of those with known trends, 56% have populations in decline.