By Dr. Jenn Ballard

It was about five years ago that I had my first opportunity to work with denning black bears. One of the first things I was told when I started was that I needed to carry a big stick. Honestly, I thought they were joking. They weren’t. A walking stick, a painter’s extension pole, it really didn’t matter as long as I had something. I quickly learned that a walking stick is the duct tape of the bear woods. When you’re hiking rough terrain, it lends balance. When you’re crossing a creek, it tests depth and footing, sometimes serving as a mini pole vault. When you’re trying to give a dose of anesthetic, it can be anything from a distraction to a delivery device. And when everything is wrapping up and the drugs are wearing off, a long stick is a good way to check a bear’s wakefulness from a safe distance. Observers often laugh about our sticks, joking about a lack of confidence in the technique or referencing the slightly ironic ‘don’t poke a sleeping bear’ idiom. I sometimes laughingly refer to my walking stick as a high-tech anesthetic monitoring device (but to be fair, I’m a vet not a comedian).

As luck would have it, the Christmas before my first bear den season I was gifted a handmade walking stick from my brother-in-law. A timely gift for sure, but I doubt he could’ve predicted the uncanny connection between his choice of material and its later use. His gift was honed from a native southeastern tree called Devil’s walking stick (Aralia spinosa). Aptly named, this medium-sized tree tends to have a straight trunk with a relatively small diameter, thin bark, and few branches. From a distance, it looks like a perfect walking stick waiting to be plucked from the midstory, but up close, sharp thorns dot the trunk and cluster in rings around the leaf scars. I can easily imagine that only the devil himself would be ornery enough to grab hold of this tree in its natural form. The devil…or maybe a bear.

Devil’s walking stick isn’t a valuable forestry commodity by any means, but the plant does have some interesting characteristics. The doubly, sometimes triply, compound leaves are among the largest of any temperate tree species in North America. Clusters of white flowers bloom from the leafy crown in the summer and give way to glossy black fruit late in the season, but the most intriguing detail I remember learning about is its selective use by bears. With its berries protected high in the crown of this thorny plant, the tree’s fruit is relatively inaccessible to many species, but black bears are not so easily deterred. They simply push the brittle trees over with their thick-padded paws to gain access to the crown and its fruit. Devil’s walking stick is a great example of how black bears flex their environments to meet their needs where others cannot.

Despite being classified as carnivores, black bears are truly a quintessential omnivore. Even their teeth attest to the flexibility of their palates. Their front teeth consist of 12 incisors for nipping and cutting, filling the space between their four powerful canine teeth. Sixteen premolars follow, but are nominal at best and may be lost with age, leaving a gap between the canines and molars. This gap, known as a diastema, is something of a dietary tell. Diastemas are a prominent feature in the dentition of herbivores like deer and rabbits, but the gap is absent in obligate carnivores. The intermediate nature of the diastema in black bears hints at the intermediate nature of their diets. Bear dentition is rounded out by a set of ten molars for crushing and grinding, another notable contrast to obligate carnivores, such as bobcats and mountain lions, that sport only four molars each.

With teeth meant for variety and a geographic range that covers a wide array of North American ecosystems, it’s little wonder that black bears demonstrate high levels of dietary flexibility. Overall, their diets consist of animal proteins, vegetation, nuts, fruits, grains/agricultural crops, and other assorted fare, but the specific foods and the ratios of these components vary between ecosystems, seasons, sex, and age classes. Theoretically, black bears seek an optimal balance of proteins, fats, and carbohydrates that can maximize their ability to gain muscle mass and store fat. In reality, they rarely hit this perfect balance on any given day, instead taking advantage of whatever food items are readily available and often mixing food types. In essence, bear foraging behavior is a calculated balance between the amount of energy a bear needs, the amount of energy a food source can provide, and the amount of energy the bear will have to expend to access it. Because energy needs and nutrition rates are a function of body size, these calculations change as bears get bigger.

After emerging from hibernation, black bear diets progress from early spring vegetation with relatively low nutritional value to a period of high protein consumption as deer (and similar species) drop their fawns on the landscape. As fawns grow and get harder to catch, bears’ summer diet transitions to a combination of insects and fruit, sometimes supplemented with crops like corn. Throughout the summer, native plants take turns providing a smorgasbord of high-energy fruit. One study in Grand Teton National Park identified over 21 species of fruiting plants utilized between the foraging behavior and scat contents of black bears and, to a lesser degree, grizzlies. Another study identified at least ten fruit species used by Louisiana black bears in the Tensas River Basin.

In some systems, research has shown that bears play an important ecological role by dispersing seeds from the fruits they consume. Late season fruits, from the likes of devil’s walking stick, may provide the last tastes of summer before bears transition again to take advantage of hard mast (i.e. acorns and other nuts). It is during this transition to autumn that many states hold their fall bear hunting seasons and observant hunters go afield looking for the telltale signs of bear activity. If you happen to be hunting in the southeastern US, bear hunting gurus will tell you that clusters of this prickly little tree are a very promising sign.

References:

Benson JF, Chamberlain MJ (2006) Food Habits of Louisiana Black Bears (Ursus americanus luteolus) in Two Subpopulations of the Tensas River Basin. The American Midland Naturalist 156(1):118-127.

Costello CM, Cain SL, Pils S, Frattaroli L, Haroldson MA, van Manen FT (2016) Diet and Macronutrient Optimization in Wild Ursids: A Comparison of Grizzly Bears with Sympatric and Allopatric Black Bears. PLoS ONE 11(5):e0153702. Doi: 10.1371/journal.pone.0153702

Harrer LEF, Levi T (2018) The primacy of bears as seed dispersers in salmon-bearing ecosystems. Ecosphere 9(1):e02076.10.1002/ecs2.2076