Nearly all of Alderney’s 8,000 gannet nests are contaminated with plastic pollution, island conservationists say.
As recently as 20 years ago, only small quantities were seen in the nests, the Wildlife Trust said.
The plastic build-up in the breeding colonies is killing the seabirds, with some entangled gannets found hung or missing legs, it added.
Around 2% of the global gannet population is thought to visit Alderney – the northernmost Channel Island.
The plastics are largely from fishing industry rope or line, the trust said.
The island is 10 miles (15km) from France and home to 2,000 people.