Minnesota’s wolf population was stable in 2015 for the third year a row, state wildlife researchers said Monday in their latest survey of the animal’s numbers.

The Minnesota Department of Natural Resources (DNR) estimates that there are 2,221 wolves in the northeastern corner of the state, down slightly from the 2,423 counted in the winter of 2013-14, but not a significant difference.

Wolf numbers fluctuate with the number of deer, their primary prey, and the severity of the winter, wildlife officials said. This year brought a mild winter and a drop in deer numbers, said Dan Stark, the DNR’s large-carnivore specialist, so wolf numbers have declined slightly. The shortage of prey also showed up in an increase in pack size and in larger than normal hunting territories for each pack — an indication that the wolves have to roam farther to find prey.

Pack sizes, on average, increased from 4.4 to 5.1 wolves, and their average territory increased from 58 to 73 square miles last winter.

Minnesota launched a wolf hunting season two years ago after the animal was removed from the federal endangered species list. But that ended last year, after a federal judge put the wolf back under federal protection.

Josephine Marcotty