Sierra wildlife prepares for winter’s arrival
November 23, 2017
The shift from fall to winter is one of the most dramatic changes to occur in the Tahoe region. Just take a few photos of the mountainside and compare them in August to January and you might not even be able to tell it's the same place. Being that temps drop, snowpack rises and food becomes scarcer, it begs the question: What do the animals do during this time?
Many people think of birds when they hear the word migrate, but one of the main species that migrate out of high Sierra are deer. "All the deer that are prevalent in the Tahoe basin during the summer all have to come down and find winter range somewhere else," said Tricia Dutcher, wildlife educator at Nevada Department of Wildlife (NDOW). "The deer will be spread out all over the mountain in summer, but they tend to congregate in just a couple areas in the winter. That's usually because the food, like bitterbrush and sagebrush, are plants that keep their leaves green all year round and that's what the deer will eat."
The severity of winter, as well as the speed at which winter settles in, also can alter where deer or other species are able to go and if they will be able to survive, Dutcher went on to explain. Some migrate over a period of time, so a sudden change in weather can leave those animals vulnerable. "Some of the animals that might be slowly migrating can get stuck up there," said Dutcher. "Then the mortality rate goes up because it takes so much energy to walk through the snow."
The timing of a snowfall can be just as influential in mortality as any other factor. "Having a big snow that melts off slowly can be good because there isn't flooding downriver, but that can upset seasonal cycles," said Dutcher. "A late snow blast can change when the berries and fruits come out, and when the insects start pollinating. If those timings don't match up, you could have a year without berries, even though there was enough water. That's what can affect the wildlife later in the year."
Not all animals are herbivores, however, so things like nuts are berries aren't in their diets. An animal that probably isn't going to be eating berries is the mountain lion. As Dutcher explained, mountain lions have a set diet that usually will not change during the year.
"Some animals will switch their diet in the fall or winter, but mountain lions are obligate carnivores so they only eat meat, and they're active all winter because they can't store enough fat," said Dutcher.
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Mountain lions already have a very large range in which they hunt and winter can sometimes increase that range even farther. "They'll make kill, eat it and keep going," Dutcher said. "In the winter, with a lot of snow, they're going to have to have a large range so they can keep moving and find that food."
Having food left out by humans influences some animals. The Tahoe region has many bears, for example, that stay more active in winter due to trash or other attractive items left outside. But it's not just the bears that are taking advantage, according to Jason Holley, supervising wildlife biologist at California Department of Fish and Wildlife (CDFW).
"We had some marten that were near the top of Heavenly Ski Resort that were reported," he said. "They were getting underneath homes and nesting. Most animals like these or bears will hibernate because a lack of natural food supply in the winter, but available food will change that." Marten are small mammals that resemble a weasel.
One thing to keep in mind, other than being mindful of where you are leaving trash and food items, is that lake level animal activity can differ from higher elevations.
"Tahoe is kind of unique because you don't always get a heavy snowpack at lake level," said Holley. "This past winter was an exception because most wildlife were forced to either leave the area or hibernate, but most winters the animals will be active at lower levels." He explained this activity could be anything from bears to rodents.
Another interesting thing about some species of wildlife in the Sierra is the way their coats have adapted to winter. "Some have become so adapted that they will have different appearance from summer to winter," said Holley. "The ermine, which is like a forest weasel, will turn white in the winter. The snowshoe hare is another species that has a white coat that is adapted to winter." The coat adaptation helps with survival and hiding from predators.
According to Holley, that often it isn't predators that will influence survival of certain animals, but human behavior. Since rodents can enter homes in winter, more rat poison may be used during this time. "There are some effects of rat poison that we've been seeing in our necropsy of bears and other animals," he said.
As an example, if a rat is poisoned and is eaten by a hawk, the hawk can be poisoned, and if a bear eats the hawk, the bear can become ill. "A lot of people use rat poison and they aren't aware of the secondary or even tertiary effects. It's best to remove that from your strategy if you want to protect the web of wildlife."
Dutcher said that there are a lot of factors that will come into play when it comes to wildlife survival and that drought or heavy precipitation can be just as influential as the other.
"It's interesting because when you get a lot of water that causes vegetation growth, and that growth fuels fires," she said. "Where we're having wildfires in Nevada, that's winter habitat for a lot of wildlife. There will be higher erosion rates on those lands and animals that would normally migrate there will have to double up on a healthy habitat with can cause stress on the land. We're trying to do some restoration planting to get those lands developed back as fast as possible."