Story highlights Hundreds of dead birds are found on shore, authorities say

It's not clear what killed them

The discovery of the dead birds comes weeks after hundreds of dead dolphins were found

The dolphin deaths remain a mystery

Authorities in Peru are investigating the death of over 538 pelicans, along with other birds, on the northern coast of the country, the Peruvian ministry of production said Sunday.

The new environmental investigation comes on the heels of an incident earlier in April when 877 dolphins washed up dead on the same stretch of coast.

It was not immediately clear if the deaths were connected.

The birds appear to have died on the beach, and more tests are needed to determine the cause of death, the ministry of production said.

The Peruvian Sea Institute surveyed about 43 miles (70km) of beach coastline on Sunday and estimated that 592 birds were dead along the shore.

State-run TV Peru estimated that up to 1,200 birds had been found dead on the 100 miles (160km) of northern shoreline extending from Punta Negra in Piura to San José in the state of Lambayeque.

The deaths began less than two weeks ago, local fishermen say.

The investigation into the mystery surrounding the dolphins is still ongoing. Peruvian Deputy Environment Minister Gabriel Quijandria told CNN the dolphins may have died from an outbreak of Morbillivirus or Brucella bacteria.

The Peruvian government has put together a panel from different ministries to analyze a report by the Peruvian Sea Institute (IMARPE). Officials have been able to conclude that the dolphins' deaths were not due to lack of food, interaction with fisheries, poisoning with pesticides, biotoxin poisoning or contamination by heavy metals.

"When you have something this large, my gut would tell me that there's something traumatic that happened," Sue Rocca, a marine biologist with the Whale and Dolphin Conservation Society, told CNN. She raised a number of possibilities as to what could have killed the animals, including acoustic trauma.

Preliminary reports ruled out that seismic sound waves created by oil exploration in that stretch of sea could have killed the birds, the environment ministry said.

They also expressed concern for the fishermen in the area and restated their commitment to protecting the country's marine ecosystem.