The discovery of over 500 dead penguins has scientists puzzled in the Brazilian state of Rio do Sul. Preliminary examination of the bodies showed they bore no injuries or oil stains and were well-fed.

The 512 penguins were found between the towns of Tramandai and Cidreira by residents of the area, who then notified the environmental patrol.

Investigators from the Brazilian Center of Martine Studies (Ceclimar) have taken a sample of 30 of the birds to try and ascertain the cause of death. The results of their study will be available in a month’s time.

Magellenic penguins breed in large colonies at the very tip of the Latin American continent in the South of Chile and Argentina. Between the months of March and September the birds migrate north in search of food.

Reports of penguin deaths on Brazil’s coasts are not uncommon, many animals dying of starvation or exhaustion during their migration. However, the scale of this incident and the fact that the birds seemed to be in good physical condition has set this case apart.

A Ceclimar official told Brazilian news agency Globo the deaths of these animals was “normal” at this time of year in Brazil given their mass migration. However, the “number of animals found dead in such a small area was cause for concern.” “They showed no signs of exhaustion and were most likely well-fed, so a more in-depth investigation is needed to determine the cause of death,” the official told Globo.