© North American Bear Center

Black Bear Box™ Manual

Section 3

Why Study Diet? How many ways can studying diet help us understand the lives, problems, travels,

and relationships of black bears? Here are a few questions it helps answer.

1. What are bears’ favorite foods around Ely? Tent caterpillars, ant pupae, and hazelnuts top the list with Junberries and wild sarsaparilla berries close behind. Black bears seek a variety of foods—not just easy calories. They prefer their favorite natural foods over most foods people provide, although sunflower seeds are a favorite.

2. Are any foods especially important to black bear reproduction around Ely? Young females often do not get fat enough to produce a first litter until there is a good hazelnut crop. First litters come at ages 3 to 8, depending upon food.

3. Why are black bears usually solitary? Their favorite foods grow in patches too small to share.

4. Why do some of Ely’s bears travel to the North Shore? The North Shore’s milder climate and deeper, more loamy soil produces more acorns, hazelnuts, dogwood berries, and mountain ash berries.

5. Does weather affect nuisance behavior?

A cold, rainy spring means fewer ant pupae, hungrier bears, and more nuisance problems in spring and early summer. A late frost or summer drought can ruin berry and hazelnut crops and drive bears to bird feeders and garbage. Dry summers that ruin berry crops can increase ant pupae and mitigate nuisance problems (as in 2007).

6. What dictates the timing of hibernation? Hibernation is genetically timed to fit regional norms of food shortage. Around Ely, important foods become scarce in September, and bears begin hibernating in late September or October.

Black Bear Adaptations for Obtaining Food

Keen sense of smell A vomeronasal organ in the roof of

the mouth for enhancing taste and smell

Strong curved claws to climb trees and rip logs

Strength to turn over rocks and logs to get colonial insects

Strength to bend branches to reach buds, catkins, leaves, and fruit.

A long, sticky tongue to reach into ant colonies

Sensitive, mobile lips to pick berries Sensitive, mobile lips and tongue to

separate food from debris. Beyond that, a black bear can ingest a mouthful of mixed nuts, distinguish the less preferred varieties, and drop them while retaining the good ones.

Color vision to find berries Detailed close-up vision to

coordinate the use of a single claw for delicate tasks

A reflective tapetum lucidum behind the retina to aid night vision.

Canine teeth to rip open logs, capture young prey, and pull apart carrion.

Incisors to nip green vegetation. Broad, flat molars and

premolars to crush acorns, nuts, and bones.

Reduced 1st, 2nd, and 3rd premolars to create a space (diastema) to strip leaves from branches pulled sideways through the mouth

A 2-part stomach with an expandable fundic region to hold a large volume and a muscular gizzard-like pyloric region to grind the pulp off small fruits and enable black bears to quickly ingest berries without chewing

Long memory of feeding locations

Mental and navigational abilities to move long distances into unfamiliar areas, return home, and remember feeding locations

Food & Habitat

Preferred Foods: Nuts, acorns, fruit, insects, succulent greens. Meat and less succulent greens are eaten when preferred foods are scarce. A scarcity of preferred foods can result in failed reproduction, stunted growth, failure to add optimal amounts of fat, and death of young bears, especially cubs. Ideal Habitat: Black bears like large forests with a variety of fruits and nuts. Many kinds of berries and ants are especially productive in sunny openings. Lowlands and wetlands add succulent vegetation. Pools and streams help bears cool off. Mothers with cubs prefer large trees (over 20 inches in diameter) with furrowed bark (like white pines or hemlocks) for bedding

sites and refuge.        

Vegetation Leaves and flowers form the largest, most dependable portion of the black bear’s annual diet around Ely—especially in spring and fall.

But not just any vegetation will do. Bears lack the intestinal micro-organisms to digest fibrous vegetation high in cellulose and lignin. They seek tender plant parts with nutrients in a digestible, fluid form and with few toxic or distasteful secondary compounds.

In spring, many young plants fit that description. Early foods are catkins (flowers) of aspen, willow, hazel, and alder. Emerging leaves, grass, and small plants come next. Aspen leaves are a major food for a couple weeks. Large-leafed aster leaves are favorites for a few days when they are small and furled.

Summer foods include wild calla, jewelweed, wild lettuce, clover, vetch, peavine, cattail, and grass.

Bears follow nutrient concentrations, eating different plants and plant parts in different seasons. They eat cattail leaf tips and roots in May and fleshy leaf bases in July and August.

Green vegetation alone is not enough for black bears to thrive and reproduce. In years when nuts, berries, and ant pupae are scarce, vegetation

enables adults to survive, but many cubs die and many females remain too lean to reproduce.

Hazelnuts, a favorite food Hazelnuts are one of the most important and preferred bear foods around Ely. Across North America, availability of hard mast (nuts and acorns) is a major predictor of bear growth and reproductive success. In the eastern United States, acorns, hickory nuts, beechnuts, and hazelnuts make the eastern deciduous forest the top black bear habit of North America. Most bears there produce first litters at 3 or 4 years of age. In northeastern Minnesota, lack of hard mast is the major reason bears here do not produce litters until 6.3 years of age, on the average.

Most hazelnuts around Ely are beaked hazelnuts (Corylus cornuta). In the occasional year when nuts are abundant, bears gain extra weight, nuisance activity is infrequent, fewer bears go to hunters’ baits, and pregnant females go on to produce healthy surviving cubs. They begin eating the soft developing nuts in June and make them their main food in July & August when the nuts ripen.

A good patch of hazelnuts can draw bears from long distances. On July 30, 1991, researchers watched Terri, a 6-year-old female with cubs, put her nose into the southeast wind and lead her cubs out of their territory on a 3-day, 41-mile trek to the best hazelnut patch the researchers ever saw. Hazel bushes loaded with nuts extended over 6 miles from Finland, MN, past Tetegouche State Park.

That was the first time Terri ventured more than a few miles outside her territory in her lifetime of being radio-tracked. At that same time, 4 other radio-collared bears

moved similar distance upwind to the same patch.

Terri and her cubs remained in the patch for nearly a month. Researchers watched how they extracted nuts from the bristly outer husks. They bit the husk to split it and make the nut pop free into their mouths. They gave each nut one or two chews with their broad, flat molars before swallowing it.

On September 4, at 5:30 PM, the family re-entered its territory and stepped onto a scale. Terri weighed 174 pounds—a good weight for a lactating female. The cubs were a whopping 66 and 70 pounds--the heaviest the researchers had seen.

How many hazelnuts can a bear eat in a day? Terri’s sister Patch provided data on that three years earlier. Patch allowed researchers to count how many nuts she ate in two 24-hour periods. She ate 4081 hazelnuts (about 12 pounds) on September 5 and 4,225 hazelnuts (about 12.5 pounds) on September 6. Where red squirrels piled nuts at bases of trees, she moved from tree to tree, sniffing each base until she hit one with a pile. Caloric intakes exceeded 12,000 calories on each of those days.

The bears’ greatest competitor for hazelnuts is probably the filbert worm (Cydia latiferreanus). It begins life as an egg in the hazelnut flower, grows up eating the developing nut, and exits the empty shell in late summer. Bears can tell in an instant whether a nut is good or empty. When most of the remaining “nuts” are empty, the bears shift to other foods.

This black bear stomach is full of dogwood berries. The expandable fundic region contains intact white berries that will pass through the constriction into the pyloric region where thick, muscular walls remove the skins and grind the pulp off the dark seeds. The gizzard-like pyloric region enables bears to swallow berries without chewing. The seeds remain intact and viable, making bears a major disperser of seeds from their favorite fruits.

Berries Berries are important foods wherever black bears are found. The major berries around Ely are sarsaparilla berries, juneberries, cherries, dogwood berries, blueberries, and raspberries. Other berries are present but are scarcer or less preferred. Baneberries and blue bead lily berries are common but not eaten.

Berries and hazelnuts are most abundant in July and August, making those months so important to survival, growth, and reproductive success that bears around Ely end mating by the time the major foods ripen. In eastern states where the main berry and nut season is autumn, mating continues longer into the summer.

Black bears can eat up to 30,000 berries on a good day. Berries contain anti-oxidants, and some of the seeds contain vitamin B-17 (a.k.a. amygdalin or laetrile), which some consider an anti-cancer compound. Cancer is rare among wild bears.

Bears can eat so many berries because they efficiently gather them with their lips and swallow them whole. The berries enter a two-part stomach, which

Canada plum pits, actual size

grinds the pulp off the seeds, leaving the seeds intact. This makes black bears important seed dispersers—one of a few animals that can disperse large seeds like Canada plum (Prunus nigra).

When berries and hazelnuts run out in September, there is little to eat, so Ely bears enter dens in September or October.

Meanwhile, black bears in eastern states are beginning their most important foraging period when acorns, hickory nuts, and beechnuts all become available.

The longer availability of food in eastern states means females can reach maturity and produce their first cubs in 3 or 4 years, while Ely bears don’t have cubs until 6.3 years, on the average. June 26, 2009

Yellowjacket larvae in a brood comb

Hornet Larvae Hornet larvae reach peak abundance in mid to late summer. Around Ely, bald-faced hornets and some yellowjacket species build the familiar above-ground nests, but most yellowjackets nest underground. Bears raid up to 17 hornet nests per day, most of them underground. They endure

stings to reach the brood comb and eat the larvae before hurrying away, wiping hornets off their faces and shaking hornets off their fur. Hornet nests become empty by late September. By then, the larvae have emerged, workers have died, and queens have burrowed underground for the winter.

8-25-09

Yellowjacket

Bald-faced hornet

Tent caterpillars

This video from June 22, 1990, shows Terri eating forest tent caterpillars (Malacosoma disstria). Terri is the 146-pound adult female that revealed to the world that black bears eat “army

worms,” as they are locally called.

During outbreaks, tent caterpillars become very abundant, but most animals and birds do not eat them. Stiff hairs on the caterpillars can coat the stomach and cause digestive problems. The only northland bird that regularly eats them is the black-billed cuckoo, which periodically sloughs the lining of its stomach to get rid of the hairs. No one knows how bears deal with the hairs.

Ely researchers accompanied Terri for three 24-hour periods during the outbreak of 1990. Each day, Terri began eating them

at first light and bedded down for the night when it became too dark to see them.

Her droppings were mainly caterpillar skins. Researchers collected the droppings, counted the skins, and discovered that Terri ate:

24,740 caterpillars on June 17, 25,192 on June 22, and 16,896 on June 24.

During the peak of the outbreak, she ate 20-22 pounds of caterpillars per day. Her total consumption was less than 1 percent of the 115 tons of caterpillars in her 2,600-acre territory. She did not eat enough of them to keep them from defoliating half of her territory. Although tent caterpillars are bear food, their defoliation reduces berry production, so bears get no fatter in years of outbreaks than in other years.