SYDNEY, Australia — Australia’s northern quolls are small animals with big appetites — and they are eating themselves to death.

Nocturnal marsupials, about the size of squirrels, quolls once roamed all of Northern Australia. But a disposition to eat just about any animals smaller than themselves led to a steady diet of cane toads, an invasive and poisonous species.

Since the 1900s, quoll populations have plummeted. In parts of Cape York Peninsula in northeastern Australia, toad-eating quolls were completely wiped out, and the animal has been considered endangered nationwide since 2005.

But in one area of Queensland, scientists noticed, quolls did not have a taste for the deadly toad and local populations were thriving. The secret to their success: a gene that made them averse to eating toads.