JACKSON, Wyo. — March presents a challenging time of the year for local wildlife, but certain species are better adapted to make it through the end of winter.
According to the Grand Teton National Park Foundation, March is especially tough for wildlife in the Greater Yellowstone Ecosystem (GYE) because winter fat reserves have been depleted but plants are still in the earliest, limited stages of growth. Without the ability to sufficiently forage, the lack of fat reserves near the end of the season can compromise an animal’s ability to survive.
Tyler Greenly, professional wildlife guide with Jackson Hole EcoTour Adventures, says most local herbivores spend the summer months building up fat reserves to sustain them through the winter. Greenly tells Buckrail that many of those animals are also often pregnant by March, so they’re depending on fat reserves not only for their own survival “but for the survival of their future offspring.”
While dependence on winter fat reserves is shared among herbivores, Greenly says the strategy used to acquire the food varies between species. As an example, Greenly says elk really benefit from forest fires that allow lots of grass and wildflowers to grow at high altitude for them to eat; the opposite is true for moose. Greenly explains that moose need shade in the summer to help prevent overheating, and in areas where forest fires have burned down trees, moose will be too uncomfortable in hotter temperatures to forage.
Research from the Wyoming Migration Initiative shows that migration plays a key role in the amount of fat an animal has on its body before winter arrives. Greenly points out that in Jackson, most large herbivores migrate and access areas with rich summer food to give them a survival advantage during the winter. As an example, mule deer performing long migrations have shown higher fat content on their body than deer that don’t migrate.
Greenly says “casualties of winter,” or carcasses, can still be seen this time of year. He notes that animals aren’t just starving, but also dying from secondary effects of disease exacerbated by the lack of available nutrition.
The winter-killed ungulates don’t go to waste, though. As male grizzly bears start to emerge in the second half of March, Greenly says they immediately start scavenging on those moose, bison and elk carcasses. A hard local winter like 2023 might mean those male bears will feed well, but Greenly emphasizes that harsh winter conditions also prevent female herbivores from carrying their pregnancies to term. This means lower calf numbers in May when female grizzlies come out of hibernation and need the protein to have energy for raising their own cubs.
Greenly says moose tend to do pretty well in March because, as browsers, they feed primarily on food that sticks up above the snow. In this later winter period, they move into river corridors to feed on willows and cottonwoods. Wolves also do incredibly well this time of year, because it’s relatively easy for them to find food as their prey concentrates in the valleys for the winter. Mountain lions are consistent throughout the year due to their adaptability.
Regardless of the level of adaptation, Greenly tells Buckrail that avoiding winter closure areas and slowing down for wildlife on highways are important ways that the public can still help alleviate some of the late winter pressures on local species.
