MANGARATIBA, Brazil (AP) — All the locals knew the island just west of Rio de Janeiro was teeming with cats. They left food and even brought tourists. Then the coronavirus pandemic hit, and human support dried up, resulting in a gruesome scene witnessed by fishermen: a group of cats devouring others' corpses.

Furtada Island, referred to widely as "Island of the Cats," is 20 minutes by motorboat from the city of Mangaratiba, at one extreme of Brazil's Green Coast, a vast swath of mountainous tropical forest and sandy coves dotted with hundreds of islands.

Over the years, fishermen tossed fish g...