Mullion Island, just south of Cornwall in England, seems like it should be an idyllic place. There are no permanent residents on the island, and anyone looking to step foot there needs to obtain a permit first. But the isolated patch of land is plagued by a problem that's common in cities: Rampant pollution. Rubber bands have been turning up there by the thousands, and experts think the problem stems from the bands' resemblance to worms, Smithsonian reports.

The rangers who managed the island owned by the National Trust were initially baffled by the appearance of the bands. The knew they weren't coming from the site's visitors, so something else had to have been transporting the trash there.

Birding organization West Cornwall Ringing Group investigated the mystery further this year. Mullion Island is a sanctuary for gulls and other types of seabirds, so the researchers visited their old nesting area to clear the built-up waste and possibly identify its source. They found what they were looking for in pellets of bird poop: The feces contained remnants of rubber bands and fishing line, indicating that the birds had been mistaking them for food. They likely picked up the bands while looking for food on the farms of nearby Cornwall. Many of these farms grow flowers and use rubber bands to secure them together, and scientists believe birds searching for food in the fields then eat the bands.

If the Mullion birds are swallowing rubber and plastic and feeding it to their young, that could have disastrous consequences for the population. Researchers reported that the 2019 nesting season was "disappointingly poor" for the 70 pairs of great black-backed gulls on the island. The presence of litter on the island was likely just one factor at play: Warming seas and dwindling fish stocks have driven the decline of seabirds across the UK in recent years.

[h/t Smithsonian]