Predatory Mice.

The mice of Gough Island have turned carnivorous and are threatening the existence of the Tristan albatross, which is three hundred times their weight:

Nearly three feet (one meter) tall, a Tristan albatross chick can weigh
up to 22 pounds (10 kilograms), or about as much as a turkey. Gough
Island mice weigh just 1.2 ounces (35 grams) on average.

While the albatrosses know how to defend themselves against larger predators, they aren’t "programmed" to deal with mice:

Video cameras revealed one pack of ten mice feeding on a Tristan
albatross chick’s wounds as it nested on the ground. Footage also
showed mice devouring Atlantic petrel and great shearwater chicks.

The birds did not fight off their attackers, even as some mice fed inside the body cavity of one albatross chick.