Last summer, Kerry Beaudry heard yelping from her German shepherd, Holly, and went outside to investigate. What she found still gives her chills. A small, mangy creature was on top of Holly, digging its claws into the scruff of her neck and gnawing at her face.

“I had never seen anything like it,” Ms. Beaudry recalled. “I didn’t know what it was. It kind of looked like a fox. But it was very, very ratty looking and had fangs and claws. It was creepy looking, but not that big.”

The animal was a fisher, a weasel-like predator of the deep woods that was saved from extinction in the Northeast and Midwest and has migrated into suburban backyards.

The small, sleek animal has cultivated a reputation as a ferocious killer of small pets, including cats and chickens, putting animal owners on edge.

Okay, it’s not as exciting as David Baron’s mountain lions, but it’s the same phenomenon at work.