Seabirds are much more likely to die from ingesting balloon fragments than hard plastics researchers have found, as they warned about the "globally recognised threat" of plastics in the oceans.
While soft plastics such as balloons only make up around 5% of items ingested, they account for more than 40% of the deaths.
Overall, balloons are 32 times more likely to result in death than ingesting hard plastic, with almost one in five birds dying from ingesting the debris.
Lead author Lauren Roman said the leading cause of death among the birds her team studied was "blockage of the gastrointestinal tract", which results in infections or other complications.
Publishing the findings in the journal Scientific Reports, the scientists said the implications from the study will provide identifiable policy targets to tackle the problem.
The approach for the study was first developed for turtles before being applied to seabirds.
The team studied the carcasses of 1733 birds, finding 557 had ingested marine debris.
"The evidence is clear that if we want to stop seabirds from dying from plastic ingestion we need to reduce or remove marine debris from their environment, particularly balloons," Roman added.
Currently half of the world's seabird species ingest debris, with populations in Australasia being hardest hit.