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GB399 is commonly referred to as "the matriarch" in Grand Teton National Park (GTNP). She is arguable one of the most iconic and famous grizzlies in the ecosystem, thanks to photographers, and visitors. GB399 is 21 years old. She was captured and collared on August 25, 2016 with a new collar for research purposes. Last year her only surviving cub-of-the-year (COY) was struck and killed by a vehicle inside GTNP. With much skepticism, she surprised many by emerging from her den this spring with two new COY. Many were fortunate to observe GB399 the past several evenings foraging with her cubs on berries. Berries and other fruits are typically consumed by grizzlies in late summer going into fall. Because of their availability, berries and other fruits make up a very small portion of grizzly bear diets. Berries are a great source of carbohydrates to bears; that in combination with high protein foods (meats, etc) maximizes the grizzlies ability to promote fat growth and fat storage. In the coming years, it is possible that as whitebark pine fails and grizzlies begin to shift to other sources, that berries may become a critical component in their summer-fall diets. This has already happened in the Northern Continental Divide Ecosystem, where whitebark pine is almost non-existent and has disappeared; now berries make up nearly 85% of the summer-fall diet (Mattson et al. 1991a, McLellan 2011, Fortin et al. 2013, Erlenbach et al. 2014, Ripple et al. 2014, Ripple et al. 2015, Costello et al. 2016a)
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Hayden Valley in Yellowstone National Park is one of the best places to have the opportunity to view grizzly bears. The experience is enhanced even further when visitors have the opportunity to view a bear feeding on a carcass. Grizzlies are classified as omnivore generalists, meaning anything that may have some sort of nutritional value may be part of their diet (Robbins et al. 2004). Grizzly diet in Yellowstone consists of more than 260 plant and animal species, with plants making up nearly 70% of that number. Typically, contemporary adult females and sub-adult’s diets consist 60% of plants and 40% of meat, whereas contemporary male diets consist 80% of meat and 20% of plants (C.T. Robbins, 2006). Elk, trout and other meats that are consumed by grizzlies are approximately 90% digestible. To the contrary, plants and forbs such as dandelions and clover may only be approximately 40% digestible (Pritchard & Robbins, 1990). Being omnivore generalists, grizzlies seek to find and consume the most nutritious foods. Because of this, their diets do change, and shift overtime based on the abundance and availability of given food sources. Elk are an important food source to grizzly bears during in spring, early summer, and fall, even with numbers decreasing in certain areas of the park. In the Yellowstone Lake area, male grizzly bears feed on an adult elk carcass about every 4 days; females every 14 days. However, feeding on ungulates is very opportunistic, meaning grizzlies must feed on other food sources (Gunther and Renkin 1990, Barber-Meyer et al. 2008, Fortin et al. 2013) One of the more visible grizzly bears in Yellowstone National Park is GB815 and her 1 remaining yearling cub. Last May 2016, she was observed with three cubs of the year (COY). This year, she was first observed this year on April 27, 2017, with only one surviving yearling, pictured below. Jort Vanderveen was fortunate enough to observe these two grizzlies near Norris, YNP this spring. Please visit Jort's Photography for more astounding images. 815 was first captured June 10, 2015 near Gibbon River in Yellowstone National Park. Her capture was for research purposes; the handling agency during her capture was the Interagency Grizzly Bear Study Team. GB815 is 10 years old as of 2017. I was fortunate enough to visit the den of GB815 and look at how she constructed her winter lair. A very, very difficult place to get into; she certainly was very well fortified and protected in this environment. Unfortunately, this den is partially collapsed, and most likely will not be used again. Grizzlies very rarely use the same den twice, and with the weathering and collapse present in this structure, it is safe to say that nobody will be using this den again. Like many, this den was at the base of a tree, using the root structure largely for structural support, and was positioned with the entrance facing north. For more on den information, please review my post from July 16, 2017 which is pinned to the top of this page, or my website www.yellowstonegrizzlyproject.weebly.com. Any questions or comments please feel free to drop a line. Video to come later. During hibernation, grizzly bears inside Yellowstone National Park (and the Greater Yellowstone Ecosystem) are tasked with finding suitable areas to construct their winter dens. Typically, grizzlies in Yellowstone dig their dens on 30-60 degree slopes with northern exposures between the range of 6500-10000 ft (Judd et al. 1986). Grizzlies typically will select den locations at the base of trees on northern face. The orientation of the den can insure that significant snowfall will insulate the den during extreme temperatures (Craighead and Craighead 1972). Den construction typically takes 3-7 days, where the bear may move up to, or more than one ton of dirt and debris material (referred to as a tailings pile)(Craighead and Craighead 1972). The den constructed consists of several parts: the entrance, tunnel, and chamber. Grizzlies will typically bring bedding material into their dens, including but not limited to spruce and pine boughs; sometimes even duff. Den entrances are typically small and grizzlies "bearly" fit through them. This is to minimize heat loss during the winter; additionally, a smaller entrance will cover with snow quicker than a larger one. The den I explored today, belongs to male GB427. Males and females with cubs typically have the largest dens. The entrance of the den was just large enough for me to be able to fit my shoulders comfortable through. The chamber was so large , I could have curled up and taken a nap! |
AuthorTyler Brasington is a native born and raised Pennsylvanian, yet proud current Wisconsin resident. He graduated from the University of Wisconsin-Whitewater with a B.S. in Environmental Science. Currently, Tyler is pursuing his masters in Natural Resources with the University of Wisconsin-Stevens Point. He has worked in Yellowstone National Park under the guidance and supervision of Dr. George Clokey and Dr. Jim Halfpenny. Disclaimer: The information and views expressed on this page do not necessarily represent the views of the Department of Interior, US Geological Survey, National Park Service or the United States Government.
The Greater Yellowstone Grizzly Project
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