Workers put dead birds into plastic bags on the beach in Concepcion, Chile on May 18, 2015

Chilean authorities said Monday they are investigating what killed some 1,300 seabirds that mysteriously turned up dead on a beach.

The , which belong to the Procellariidae family, may have drowned after getting trapped in fishing nets or died from a disease such as , which is not endemic to Chile, said the country's Agriculture and Livestock Service (SAG).

They were found Sunday afternoon by visitors to a small black-sand beach in the southern town of Lenga, a cove with several hundred inhabitants who live mainly on fishing and tourism.

SAG said it was analyzing samples taken from the birds to try to determine the cause of death.

Hundreds of birds were found dead in the same area in 2010. Authorities determined they had been caught in .