Bear Necessities: Black Bear Biology

Black bears (Ursus americanus) are arguably the most iconic animal in Great Smoky Mountains National Park. People from all over the world flock here year-round in the hopes of seeing our big furry friends. Great Smoky Mountains National Park is home to more than 1,600 bears – a steady population that is supported by the 800 square miles of protected land where they have plenty of food, water, shelter, and space. This means, on average, that there are two black bears every square mile inside the National Park… pretty awesome, right? We have the highest density of black bears anywhere on Earth. Cades Cove is a particularly popular area within the Park for bear sightings, drawing in large crowds throughout all four seasons. If Cades Cove were its own National Park, it would take the bronze medal for “number of visitors per year” – with Great Smoky Mountains taking the gold and Grand Canyon with the silver. Cades Cove doesn’t necessarily host more bears than anywhere else in the Park, but because our open fields provide direct line of sight, it provides a prime spot for wildlife watching.

In the spring, about mid-April, black bears begin to emerge from their winter dens. Males will emerge first, followed by females without cubs, while females with cubs will emerge a few weeks later. Most bears den inside hollow trees, rather than caves as is commonly expected. Therefore, more often than not, one of the first things baby bears do when exiting their dens and entering the big world is climb down from a height of about 60 feet. Bears spend the spring months searching for food, like the way you forage in the fridge for a big breakfast after a long night’s sleep. Contrary to popular belief, their impressive claws are used little for hunting and more frequently for foraging – digging in the soil for roots and flipping fallen logs in search of grubs. Black bears are omnivores (meaning that they eat both meat and vegetation), but more importantly, they are opportunistic feeders (meaning they choose their meals based on opportunity and availability). 85% of a black bear’s diet consists of vegetation, such as berries, plants, and roots. Only 15% of their diet consists of meat, and the majority of this percentage is comprised of insects, grubs, and even carrion (bodies of dead animals) when available. A black bear will sometimes take down a deer or smaller mammal, however, bears hunt relatively infrequently when compared to other apex predators. This is due in large part to the amount of energy it takes to hunt, and in many cases black bears will choose to conserve energy when other options are present (such as vegetation or insects).

During the summer months, fruits and berries become plentiful in the Smokies (such as wild raspberries, blackberries, and strawberries) and it’s not unusual to see a black bear in a fruiting tree or berry bush for long stretches of the day, possibly even for a few consecutive days at a time. The summer season is also when the love happens in the Park – male black bears will search for a mate, and female black bears who are two to three years or older will be receptive. When females become impregnated, something really incredible comes into effect called delayed implantation (keep this in mind because I’ll be coming back to this topic in the next paragraph). Cubs will remain with their mothers for about 18 months, at which point they are considered yearlings. Often, females with yearlings will still be receptive to a mate in the summer months, and will run their young off by the end of the summer. Sometimes, a mother will only run off her male offspring and will allow her female yearlings to remain with her for a little longer into the fall months, because she is more likely to share territory with her daughters than her sons.

Autumn arrives as do the nuts. Beech nuts, chestnuts, and acorns are all an incredibly important food source for black bears as they prepare for the winter. They are on the hunt for about 20,000 calories every day – this is equivalent to 37 Big Macs from McDonald’s, to give you a point of reference. This is also equal to about nine pounds of nuts, which is why the fall season and the nuts it brings with it is so invaluable to black bears. Although this is roughly the amount of food every bear is searching for each day, this is specifically the number of calories that impregnated females need to attain in order to sustain a cub, and if she’s able to achieve this goal, she will give birth in the winter. I promised I would return to the topic of delayed implantation, and this is where it comes into effect – IF a black bear mother-to-be does NOT acquire at least this number of calories every day during the entire fall season, she will reabsorb the fertilized egg and will NOT give birth in the winter. In other words, delayed implantation is Mother Nature’s absolutely marvelous way of ensuring that the black bear population will never outweigh the food supply, and that there will always be the proper amount of food to support the population. The more successful a black bear mother-to-be is in her attempt to achieve 20,000 calories each day in autumn, and the more body fat she is able to accumulate, the more cubs she will be able to provide for in the winter and the more cubs she will give birth to. When you see a mama bear with three, four, even sometimes five cubs in the spring, I hope you look at her with admiration – not only does she have her paws full, but the number of her offspring directly indicates how successful she was at foraging for food the previous autumn!

Black bears will begin to den down for the winter in late November. In the southeast, bears don’t actually go into hibernation (a state of a deep, trance-like slumber during which body temperature and heart rate will decrease). Instead, they go into torpor during the winter months, which is a state of slumber during which the body temperature and heart rate do NOT decrease, and the bear can rouse at any time or even leave the den to grab a “midnight snack”. Impregnated female bears who do not reabsorb their egg in autumn will give birth to their cub(s) around early to mid-January. Bear cubs are born furless, clawless, blind, and completely dependent upon their mothers. Many scientists refer to the den as an “artificial womb” because so much of baby bear development takes place after birth while still inside the den. When the cubs emerge in the spring, they may look like newborns but are already about three months old.

This blog post is the first of three in a short series on black bears, and was specifically dedicated to discussing black bear biology. Stay tuned for more posts in the near future covering one of my favorite animals on Earth… and for more pictures like this one! Such little bundles of joy!

Picture credit goes to the very talented Jay Sheinfield.

Sources:

• Education and Interpretation Park Rangers and Volunteers with Great Smoky Mountains National Park

• Pivorun, Edward Broni., et al. Mammals of the Smokies. Great Smoky Mountains Association, 2009.

• Lix, Courtney. Frequently Asked Questions about Smoky Mountain Black Bears. Great Smoky Mountains Association, 2010.

2 thoughts on “Bear Necessities: Black Bear Biology

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s