Late last year, fishermen began finding dead dolphins, hundreds of them, washed up on Peru’s northern coast. Now, seabirds have begun dying, too, and the government has yet to conclusively pinpoint a cause.

Officials insist that the two die-offs are unrelated. The dolphins are succumbing to a virus, they suggest, and the seabirds are dying of starvation because anchovies are in short supply.

But even three months after officials began testing the dolphins, the government has not released definitive results, and there is growing suspicion among the public and scientists that there might be more to the story. Some argue that offshore oil exploration could be disturbing wildlife, for example, and others fear that biotoxins or pesticides might be working their way up the food chain.

At least 877 dolphins and more than 1,500 birds, most of them brown pelicans and boobies, have died since the government began tracking the deaths in February, the Environment Ministry said last week. The dolphins, many of which appeared to have decomposed in the ocean before washing ashore, were found in the Piura and Lambayeque regions, not far from the border with Ecuador.