Cook Inlet's coastal brown bears share the salt marsh meadows

On the evening of July 15, 2020, park staff counted 289 brown bears during an aerial survey from Tuxedni Bay to Chinitna Bay in Lake Clark National Park and Preserve. Bears can coexist in a relatively small area because of the abundance of food there. The National Park Service calls them a keystone species, as their presence reflects the productivity and protection of coastal habitats.

NPS photo by A. Jones.

Counting the bears

The scientific name, Ursus arctos, covers both brown and grizzly bears. The park flies aerial surveys twice each summer from Tuxedni Bay to Chinitna Bay to estimate how much bears use the salt marsh meadows.

The park reads this as the meadows drawing a large share of the bear population in peak season, with highly localized densities. The Dena'ina, the Alaska Native people of Southcentral Alaska, call Alaska brown bears ggagga.

Bears live and graze close together because food is abundant. NPS photo by D. Liles.

Brown or grizzly: geography

They are one species, with notable differences that come mainly from geography. Brown bears typically live along Alaska's southern coast, with access to concentrated, protein-rich foods: salt-tolerant sedges, clams and seasonally abundant spawning salmon. That lets them grow larger and live at higher densities than "grizzly" bears in the north and interior, where food is limited.

What they look like

A boar showing head size, shape and the characteristic hump. NPS photo by A. Jones.

Coastal brown bears have a massive head, a dish-shaped (concave) face and a prominent nose that detects odors from more than a mile away. They have small eyes, rounded ears and slightly curved claws 2 to 4 inches long. The shoulder hump helps them dig up rodents, roots, bulbs and clams, and supports bursts of speed up to 35–40 mph. Hearing and eyesight are equivalent to humans'. Color is not a reliable clue: they range from tan, blonde, gold, gray, silver and cinnamon to all shades of brown and black.

Bears are lean in spring and early summer, after hibernation, and gain weight rapidly in late summer and fall. Fat stores bring a male to between 500 and 900 pounds, and 1,500 pounds is possible. Females commonly weigh 250 to 600 pounds in the fall. Adults stand about 3 to 5 ft at the shoulder.

Life cycle

• Maturity and mating: females become sexually mature at 4 to 6 years. Mating runs from mid-May to mid-July, and a female may mate with several bears.
• Delayed implantation: about five months before entering the den. If a female lacks enough fat for winter, the embryo does not implant and is reabsorbed. If she is healthy, it attaches to the uterine wall and, after eight weeks of gestation, cubs are born in January or February.
• Cubs: a litter has 1 to 4, and twins are most common. They are born tiny and hairless, sometimes under half a pound, and nurse while their mother sleeps. Her milk is 20–25% fat. In spring they weigh between four and eight pounds. Lactation usually lasts 1.5 to 2.5 years.
• Family: males take no part in raising cubs. Cubs stay with the mother for 2 to 3 years, learning survival skills; then she leaves them and can mate again. Average lifespan is 15 to 25 years.

Rocky cliffs give a sow and cub sanctuary. NPS photo by D. Liles.

Winter sleep

Before winter, bears eat more and add fat that insulates them, stores energy and lowers the risk of starvation in the first weeks after they leave the den. They usually den in alpine and sub-alpine areas. This is not true hibernation but dormancy, which scientists call torpor, lasting 3 to 7 months. With large food harvests or winters with little snow, it may be brief or not happen at all.

In the den bears do not eat, drink, urinate or defecate. Heart rate falls from 40–50 beats per minute in summer to 8–10, with blood shunted mostly to the heart, lungs and brain. Active body temperature is 36.5 to 38.5 °C (97.7 to 101.3 °F), and it drops 4–5 °C in the den. Water comes from burning fat, and waste normally excreted in urine is recycled, protecting the kidneys and lean body mass. Mature females lose about 40% of their fat mass over the winter, twice as much as males, because of the energy of reproduction. After emerging, bears spend about two weeks in "walking hibernation" with a suppressed metabolism.

Home range and diet

Home range depends on food: along the coast, the more concentrated the food, the smaller the range needed. Age, sex, social status, condition, foraging habits, den and bedding areas and the location of mates also matter. Females have smaller ranges and stay near their mother's, which adds security for her and her cubs. Mature males cover the ranges of several females in estrus; subadult males disperse because of low social status and aggression from adult males. Bears defend personal space but do not normally defend home ranges.

A brown bear grazing on the meadow's "24-hour salad bar." NPS photo by A. Jones.

Brown bears are omnivorous, opportunistic feeders. They eat berries, flowers, grasses, herbs, roots, carcasses, clams, fish, insects, moose calves and other small mammals, 80 to 90 pounds of food a day in summer and early fall. The seasons shift the menu:

The Dena'ina names: berries giga; clams tiq'adi; flowers ashana; silver salmon nusdlaghi; grass k'chan; sedge tl'egh; salmon run shanlaghi; plants qinunilyaxi; moose calf k'dechiga.

Rank and behavior

Adult brown bears mostly live alone but gather during mating and where food is plentiful. They communicate with vocalizations, body posture and scent marking. Rank runs from dominant adult males (boars), to females (sows) with cubs, to subadults and juveniles. Weaker bears yield space, breeding rights and prime feeding spots with minimal or no injury. In spring dominant males court a female for hours or days, following, chasing and strutting.

Bears using vocalizations at a feeding spot. NPS photo by D. Liles.

At Chinitna Bay and Silver Salmon Creek, visitors can see bears living close together. Older boars usually avoid people unless mating or pushing juveniles around. Juveniles learn their place by being chased off or pushed from food, and can show the same pushy behavior toward people, if allowed. The park compares them to toddlers having tantrums. At Chinitna Bay, juveniles and sows with cubs bed down in small, high-cliffed spots a boar will not spend the energy to reach. Sows fight a male who gets too close. Sows with new cubs keep to the meadow edge, near trees for a quick retreat, and often use people as a buffer against boars. Cubs that flee away from their mothers during a threat can be lost for hours until they are reunited, usually through distress calls.

A sow checking the scene for safety. NPS photo by D. Liles.

Reading signals: a yawning bear may be agitated or bored; popping jaws, growling, roaring, snorting or barking mean agitation that could lead to an attack; a standing bear is getting a better look, or may feel threatened. A full-frontal approach with neck outstretched and ears back shows dominance; a sideways stance with head lowered, sitting, lying down or backing away shows subordination. Bears circle back when curious or interested in a scent, including around people. They mark trees or ground with scent to share routes and signal dominance, and bears of all ages play by chasing birds or rolling down hills.

Sources

• National Park Service, Lake Clark National Park and Preserve, "West Cook Inlet Bear Ecology," https://www.nps.gov/articles/000/coastal-bear-ecology.htm ; rewritten in hubnx's own words.