A substance which has been covering birds on the south coast is an oil additive, a university has said.
The substance - found on seabirds off the south coast of Cornwall, Devon and Dorset, and up to West Sussex - has caused burning to birds.
Plymouth University said it was a form of polyisobutene (PIB), which was used as a lubricating additive in oils to improve performance.
It added it was informing the Maritime and Coastguard Agency and the RSPCA.
Congealed on feathers
The substance was identified after analysis of a guillemot.
Chemical analyst Professor Steve Rowland, of the university's Centre for Chemical Sciences, said all the data it had gathered supported the conclusion.
He said: "It's very sticky and semi-solid, hence its acting on birds' feathers like a glue.