By Ryan Johnson

We’re going to go ahead and be party poopers: Balloons are bad, and now it is scientifically proven. A recent study published in Naturereveals that those plastic party decorations are the deadliest plastic out there for seabirds.

To make that determination, the researchers looked at the stomach contents of more than 1,700 marine birds, comparing birds killed by eating plastics with other causes such as fishing bycatch, infant mortality, and disease. They found that while balloons represent only 2% of all the plastics that seabirds ingest, they are brightly colored death balls, responsible for 42% of plastic-related deaths for the birds who eat them.

Why are balloons so lethal to birds? Because balloons look like delicious seafood snacks to the birds, but when they eat the buffet of plastic littering the planet, the balloon kills them by opening up in their stomachs, resulting in an undigestible blockage, the researchers said.

“A hard piece of plastic has to be the absolute wrong shape and size to block a region in the birds’ gut, whereas soft rubber items can contort to get stuck,” Lauren Roman, a marine scientist at the University of Tasmania and lead author of the study, told Australia’s ABC News.

While there are laws against balloon releases in many states and countries around the world, balloons can travel far. And as every parent knows, they can easily slip away from even the most eagerly grasping hand. The researchers suggest replacing those deadly plastic party favors with biodegradable alternatives, like those listed here, and keep plastic out of the ocean and out of birds’ stomachs.