The following is an excerpt from the Summer 2015 issue of Tahoe In Depth. Click here to learn more, read past issues, or subscribe today.
Climate changes can throw off key wildlife patterns
By Ruby Lyon
Tahoe Institute for Natural Science
A shifting climate affects the timing of important events in the plant and animal world. These important life cycle events—known as ‘phenology’— happen when the wildflowers bloom, when plants make fruit or new leaves, or when birds migrate or build nests. The timing of these life cycle events is intricately connected to many environmental factors, including elevation and weather.
For example, a long winter with heavy precipitation will result in many phenological events happening later in the season, while a mild, dry winter, such as those in recent years, is linked to the early arrival of spring.
Some phenological processes may be responsive to weather events and therefore can react quickly as climate shifts. For example, local sparrows, robins, and bluebirds may only descend to lower elevations during the harshest winter weather, then return after a couple of mild weeks.
This is not the case for many other organisms. Western tanagers wintering in Central America have no idea if Tahoe is having a mild winter and an early spring. They try to get here early to secure the best territory and capitalize on the brief summer flush of resources, but if they arrive too early, they may be faced with limited food and freezing weather. Migration patterns develop over many generations, and it can take a while for these patterns to shift to match changing conditions at Lake Tahoe.
With small feet and heavy bodies, Tahoe’s mule deer are not built to cope with deep snow. To make matters worse, their principal food source gets buried. Therefore, Tahoe’s deer typically move to lower elevations for the winter, with many making the shortest trip possible by heading east. Many of Truckee’s Loyalton herd will descend the Truckee River canyon to Verdi; others head north. The Carson Range deer have an easy migration to lower elevations, while deer in Christmas Valley and the Angora Burn area migrate up over Luther Pass to Hope Valley, and then down the Carson River.
It is not unheard of for deer to be caught by early snowfall and get trapped in the Tahoe Basin, and such animals usually are seen in the vicinity of Emerald Bay, where they spend the winter at Lake level. Quite a few deer have been seen at Tahoe mid-winter in recent years, and earlier this year a few young bucks were seen swimming off Pope Beach in February! The timing and routes of deer migrations are worked out over many generations, and are passed down culturally by older members of the herd. After four years of drought, it is safe to assume that many of the deer now overwintering at Tahoe have never experienced a “real” Tahoe winter, and have never learned to migrate away from an average Tahoe snowpack. Mule deer only live around 10 years on average, so additional mild winters may bring about a significant drop-off in the numbers of deer that know how to migrate…click here to read the rest of this article and more!