Scavenging seagulls don’t only raise a ruckus, but their poop pollutes our waterways, a new study finds.

Researchers at Duke University used both empirical data and their own hunches to estimate the number of landfill-dwelling seagulls in North America, finding that while the popular figure was 1.4 million, it was likely closer to five million.

Examining the loading of nutrients from two large drinking reservoirs near landfills in North Carolina — Jordan Lake and Falls Lake — the researchers used this data to estimate the total amount of phosphorous and nitrogen in bodies of water across the continent.