Ecological Studies of Wolves on Isle Royale

In February 2023, the wolf population was likely composed of 31 wolves. This is a slight increase from last year’s estimate of 28 wolves (Fig. 1). The wolf population includes an East Pack with 11 wolves, a West Pack with five wolves, three groups of at least three wolves each, and several other wolves that are either loners or only loosely affiliated with one of the smaller groups. There is evidence that pups were born into three, possibly four, litters in April 2022. For context, no litters are thought to have been born between 2015 and 2018. However, following the translocation of wolves to Isle Royale between 2018 and 2019, one litter was born in 2019, two litters were born in both 2020 and 2021, and possibly four litters were born in 2022. Thus, the reproductive success of the wolf population has steadily increased over the last five years. The per-capita kill rate, which is an indication of the rate that wolves acquire food, was 0.52 moose per wolf per month. That rate is somewhat lower than last year’s estimate of 0.71, but similar to what is expected given the number of wolves and moose currently on the island. The estimated abundance of moose is 967, which is a 28 percent decline from last year’s estimate of 1,346. Longer-term population trends suggest that the moose population had increased greatly over an eight-year period (2011-2019) but then started to decline rapidly over the last few years. The proportion of the moose population that is newly recruited individuals (i.e., nine-month-old calves in February) was 1.7 percent, which is very low compared to the long-term average. Predation rate was estimated to be 10 percent, which is similar to last year’s estimate and close to the long-term average. While predation and low recruitment were important contributors to the moose decline, starvation also played an important role.