TEMPLATE DESIGN © 2008

www.PosterPresentations.com

Polar Bears

Alexis Deutschmann

Abstract

There are five nations with polar bears: U.S. (Alaska), Canada, Russia, Greenland, and Norway.

Annual ice melts completely during the summer and forms again in winter, this is where polar

bears do most of their hunting. Polar bears have distinct territories, or home ranges, some bears

have huge home ranges while others stay in a much smaller area. The polar bear’s blubber layer,

which can be up to 4.5 in thick, provides insulation against the cold so the bear does not need to

change its metabolic rate very often. Polar bears sometimes swim in open water and it’s not

irregular for a bear to cross a distance of up to several kilometers, however their presence that far

from land is mostly accidental. The primary prey of the polar bear is the ringed seal and the bears

use the “still-hunting” technique. The ability to find a reproductive female polar bear for mating by

adult males is difficult. Through aggressive interactions, a male can reduce access to females by

his competitors. The Arctic is experiencing the warmest air temperatures in four centuries, and sea

ice losses in the summer of 2012 broke all previous records. Only 2% of the polar bear population

enters the market each year from Inuit hunting.

Habitat

Traits Body Temperature and Energy Efficiency The normal body temperature of a polar bear is about 37ｰC, similar to most mammals. The

polar bear’s tough hide, thick fur, and blubber layer, which can be up to 4.5 in thick, provide such

efficient insulation against the cold so that the bear does not need to change its metabolic rate very

often (polarbearsinternational.org 2014). As long as the bear is not exposed to wind and is

relatively inactive, it does not need to burn excessive energy in cold weather. A negative aspect to

this is that the bear overheats quickly, making activities like running a very high-energy activity

(Stirling 2011).

Weight for weight, a polar bear uses more than double the energy to move at a particular speed

than most other mammals, this results from it’s massive limbs and bulky build, especially in larger

individuals. The high cost of walking helps explain the polar bear’s preference for lying and still-

hunting instead of stalking, even when there are seals nearby on top of the ice (Mulvaney 2011).

Morphology Polar bears have 42 teeth and their dental formula is written as 3/3, 1/1, 4/4 and 2/3, a reference

to the umber of incisors, canines, premolars, and molars respectively.

Behavior Swimming

Polar bears are known for being great swimmers. In the summer, bears of all ages and sex swim

and may do so for hours at a time along a floe edge or among the floes, likely looking for prey.

Polar bears sometimes swim in open water several hundred km offshore in the Greenland, Barents,

and Labrador seas. It’s not irregular for a bear to cross a distance of up to several kilometers,

however their presence that far from land is mostly accidental (Stirling 2011). They swim dog-

paddle style with their forepaws and have their hind legs behind, sometimes serving as rudders.

Even though they’re powerful swimmers, they still often take detours of a few hundred or more

meters to avoid having to get in the water although the exact reason exactly why is not known.

Healthy polar bears are buoyant because of their body fat. The fat of adults is adequate to keep

them warm enough however, females with cubs tend to avoid swimming long distances. If it’s not

avoidable and the cub is small, the female will carry it on her back to keep it mostly out of water

(Mulvaney 2011).

Hunting

The primary prey of the polar bear is the ringed seal. It’s the most abundant and widely

distributed seal in the Arctic and it’s also the smallest, with adults weighing only 90-150lb. Their

small size is important to polar bears because it means any sized bear can successfully hunt it.

Polar bears will hunt seals in all season if they are able to be on ice but the most important times

are spring and summer, before break-up. During winter and spring, adult ringed seals have

territories beneath the ice and they’re distributed

over huge areas at low densities. The seals

maintain breathing holes by constantly scraping

the ice with the claws on their foreflippers. Later,

in spring, pregnant females give birth to single

pups in lairs they created during the winter.

Ringed seal pups are born weighing only about 12

lb at birth (Stirling 2011). They are weaned by six

weeks and by

that time they weigh about 48 lb. The high

amount of seal pups, which are not yet experience

with predators, in spring provides the most food

for the bears. To hunt seals, polar bears rely on ice.

The occasional bear has been known to kill seals in the water but successful hunting in open water

is very uncommon. Bears are far less agile swimmers than seals, which makes expending energy

by swimming both ineffective and inefficient compared to waiting on the ice.

The much larger, and far less abundant, bearded seal is the other main prey species for the polar

bear. Adults may weigh 500-800 lb (Mulvaney 2011). Because of their large size, they’re mainly

killed by large male polar bears. In some areas such as Davis Strait, harp and hooded seals haul out

near the outer edge of the pack ice in March to give birth to their pups. Despite the risks of hunting

so far from land, the caloric reward of access to so many pups is huge and some polar bears walk

several hundred kilometers from southern Baffin Island, feast heavily on the pups for a few weeks,

and then walk all the way back.

Beluga whales or narwhals that become trapped in a savsatt,

a small opening in pack ice, become easy prey for the bears

(polarbearsinternational.org 2014). When this happens, large

male polar bears harass the whales, eventually tiring them

enough to be able to seize one and drag it onto the ice. Given

the right circumstances, bears, mainly large males, are capable

of learning to capture belugas. The most valuable contribution

made by whales to the diet of polar bears is made by animals that

die of natural causes and wash up on the beach where polar bears

can scavenge with ease.

In the summer after the snow has melted from the ice, seal’s breathing holes are no longer

hidden to bears. Polar bears’ then use the “still-hunting” technique. The bear stays motionless

beside a breathing hole while waiting for a seal to surface to breathe. During the summer, about

80% of the hunting is done this way, probably because it takes a minimum amount of energy to do

so. Most still hunts last less than an hour although some may last for several hours. When a seal

does surface, the bear seizes the seal’s head or upper body and pulls it out of the hole. The polar

bear then drags the seal several meters away from the water before starting to eat (Stirling 2011).

Breeding

Territoriality, competition, and sexual dimorphism

The ability to find a reproductive female polar bear for mating by adult males is more difficult

than for other bears, primarily because of the lack of stability in the polar bears’ habitat. The

territories of adult male polar bears are usually larger than female polar bears and tend to overlap.

Because of this, a male has a chance to mate with more than one female. Through aggressive

interactions, a male can reduce access to females by his competitors. Bigger males who win more

fights mate more, thus there’s a strong evolutionary need for a larger body size. This leads to

“sexual dimorphism,” which means a distinct size difference between males and females. Sexual

dimorphism isn’t limited to just body size, the canine teeth are also much larger than those of

females, which has an impact during fights and threats (Mulvaney 2011).

Breeding behavior

Polar bears mate in the spring but female polar

bears usually don’t mate at all if they are still

accompanied by cubs. Mating takes place in April

and May but finding lone females in the Arctic is

a difficult task. The habitat most preferred by

females that need mates tends to be near the floe

edge or areas of moving pack ice where ringed

seals occur. Females focus on building up their fat

stores in preparation for a possible mating and

then pregnancy and leave it to the males to find

them. Because polar bears normally live alone and

are widely dispersed at low densities, it’s difficult

for males to find a receptive female. Often, because the priority of the males is to find females

during spring, they will go several days without hunting. When a male does find a female, if she is

alone, he begins to try to interact with her. If she is already accompanied by one or more males,

fighting will happen until the dominant male wins out (Mulvaney 2011). Once a male has secured

a female, the pair may stay together for two weeks or longer before copulations are finished.

Biology of reproductive behavior

The majority of mammals, such as seals or humans, are “spontaneous ovulators,” meaning that

the females automatically release an egg for fertilization at a certain time because there is a high

chance that there will be a male available to fertilize it. Female polar bears, who are widely

distributed as solitary animals at low densities, instead do a process called “induced ovulation”

Only after days of behavioral interaction have provided her with enough physiological

reassurance does she ovulate and then copulate over the next few days. Because the pair remains

together for several days before she’s ready to mate, this allows other adult males to locate them.

This increases the probability that her cubs will have a father that will be large, successful, and

dominant and receive the best possible genetic inheritance (Mulvaney 2011).

Denning

Getting Ready for Denning

After females mate in the spring, they only have a few short months to gain the large amounts of

fat she will need to survive and to support her new cubs in the coming fall. They need to gain at

least 220 lb of fat to have a successful pregnancy. Females tend to wean their cubs during spring

because that is when the availability of prey is greatest and is most vulnerable. In late March and

early April, millions of ringed seals dig birth lairs over their breathing holes in the ice. It’s during

the seals weaning time, when they don’t have experience yet when it comes to predators, that polar

bears feed on them intensively through spring and early summer (Mulvaney 2011). Through this

abundance of fat, female polar bears are able to gain that much fat so quickly. How long a

pregnant female is able to remain on the ice to hunt before going ashore and into a den can very

depending on the area.

Structure of Maternity Dens

Most pregnant polar bears go inland along lake edges and streams that contain beds of frozen

mud deep enough to be able to dig into. Most of the time, they have to do this because in most

years, there isn’t enough snow on the ground to form suitable drifts in which pregnant females

could dig maternity dens before the cubs are born late November or December (Mulvaney 2011).

In places like Southampton Island or the east coast of Baffin Island, there is usually a lot of snow,

so female bears can make a den wherever they like. The most common structure of the den itself is

a single chamber that’s slightly elevated from the entrance tunnel so the warm air stays inside. On

average, the rooms are about 6.6 x 5 ft and 3 ft high. The entrance tunnels are usually long but

very narrow (Stirling 2011).

Climate Change

References Cited

At the March 2009 range states meeting of the five polar bear nations, scientists agreed that

climate change is the single biggest threat facing polar bears. The Arctic is experiencing the

warmest air temperatures in four centuries, and sea

ice losses in the summer of 2012 broke all

previous records (polarbearsinternational.org

2014). The Arctic has experienced

warm periods before, but the present, rapid

shrinking of sea ice is unprecedented. It has been

linked to a build-up of greenhouse gases in the

atmosphere caused by human activity. Scientists

predict a mostly ice-free Arctic summer by 2040

unless we take action to reduce greenhouse gas

emissions (polarbearsinternational.org 2014).

Without ice, polar bears are unable to

reach their prey. Shorter hunting seasons correlate

directly with a 22% drop in the population of

Western Hudson Bay near Churchill in Manitoba,

Canada since the early 1980s (Rode 2010). A Southern Beaufort Sea population study shows a

drop in cub survival rates, as well as declines in the weight and skull size of adult males, when

compared with data from 20 years ago. Similar declines were observed in the Western Hudson Bay

population before it dropped (Rosing 2006).

Polar bears live In the Arctic in areas where they can hunt seals. There are five nations with

polar bears: U.S. (Alaska), Canada, Russia, Greenland, and Norway (Mulvaney 2011). Living in

the Arctic, sea ice has the greatest influence on the ecology of polar bears, mostly because of how

ice determines the location of their main prey, the ringed seal. Annual ice melts completely during

the summer and forms again in winter,

mainly along the coastlines of the

Arctic Ocean. Annual ice rarely gets

thicker than two meters and is more

susceptible to sunlight underneath,

stimulating algal growth. Most annual

ice is found in the continental shelf

where seal populations are high.

Consequently, that is where polar

bears do most of their hunting.

In surveys that covered about

75,000 km in the Beaufort Sea to

determine what kind of sea ice habitat

polar bears preferred, researchers

discovered a great majority of polar

bears (514 of 627) were in areas where

the pack ice regularly cracked open

because this is where young ringed

seals or bearded seals have their breathing holes (Mulvaney 2011).

In spring, pregnant females dig out dens to give birth to their cubs. About 100 of the 627 polar

bears were found in this type of habitat. In most areas of the Arctic, this habitat tends to be along

the coastlines, in large bays or fjords.

The least preferred areas are those where the ice is very rough. Not only is traveling through this

area expensive energetically and difficult to travel through, the seal’s breathing holes are difficult

to access beneath the pressure ridges and ice blocks. Polar bears also tend to avoid vast areas of

smooth ice with little drifted snow because there is not enough cover for the seal’s breathing holes,

and therefore less seals in the area (Mulvaney 2011).

Although many biologists were involved with the use and development of satellite radio collars,

Steve Amstrup was a main contributor when it came to tracking polar bears with collars (Stirling

2011). Through the late 1980’s and 1990’s, Amstrup and his team radio-tracked several dozen

individual polar bears for several consecutive years and found that polar bears have distinct

territories, or home ranges. They also found that some bears had huge home ranges including large

sections of the whole Beaufort Sea, while

others remained in a much smaller area.

The average annual home range of 75

radio-collared bears was 57,529 mi.

Home range sizes varied, the smallest

recorded was about 1,158 mi and the

largest was 230,502 mi. Home ranges

are neither distributed at random nor

spread evenly throughout the Arctic.

Ecological conditions and the

distributions of resources are too

valuable to allow that. Thus, in places

where ice conditions may be too poor

or unreliable for seal hunting, there

will be fewer home ranges. In areas

where seals are available, there may

be many overlapping polar bear home

Ranges (Stirling 2011)

.

Polar bears have shown different strategies used in different sized home ranges. In a study of

two female polar bears, both in Davis Strait, one had a large home range, averaging about 60,200

mi and traveled back and forth between islands and on pack ice well offshore. In contrast, the

second female had a home range of only about 1,500 mi and remained in a few bays along a short

section of the coast, rarely going offshore. The different strategies the two bears had were different

due to the way these two individual bears balance their energy needs to make the travel that was

necessary easier to hunt for their preferred prey. The polar bear with the smaller home range had a

diet that was mostly made up of ringed seal. Leaving the possibility that she has chosen to remain

where prey species may be small but her energetic needs would still be met as long as she remains

local. The polar bear with the larger home range had a diet that was made up of harp seal, a larger

and very abundant seal that occurs further offshore than the ringed seal. Her greater energetic

needs from having such a large home range is met by feeding on larger prey (Stirling 2011).

Home Ranges

Fig 2. An illustration of how different the sizes of home ranges can be

for individual adult female polar bears. (Stirling 2011)

Fig 3. A polar bear spreads his legs out widely to help spread

out his weight so he won’t fall into the water as he crosses a

patch of thin ice. (polarbearsinternational.org)

They have small ears because of the need to

conserve energy and smaller surface areas

lose less heat than large ones. Polar bears

have large feet, much larger than other bears

like black bears or grizzlies, in relation to

their body size. The large feet help them in

the Arctic in two major ways. First,

swimming is made easier with large, oar-like

feet to help with propulsion. Second, while

searching for prey in early winter, polar bears

cross thin ice that usually wouldn’t support a

large animal (Mulvaney 2011). Their huge

paws function like snowshoes to spread out

their weight and keeps them from falling

through the ice (Stirling 2011).

Fig 4. A Polar Bear and its 2 cubs feeding on a

Bearded Seal.

Fig 5. several polar bears dining on a

beached whale.

Fig 6. A male polar bear showing battle scars and the

female he contended for with 10 other males. (

Fig 7. The structure of common polar bear dens.

Fig 8. A cub leaving it’s den.

Human Interaction

Fig 9. A mother and her cub making the first of many long

swims across open water. (

Wildlife harvesting has been an essential part of Inuit culture for thousands of years, remaining

fundamental to Inuit social and economic well-being into the twenty first century. Under the 1973

International Agreement on the Conservation of Polar Bear, the subsistence harvest of polar bears

is an exclusive right of Indigenous peoples. Only 2% of the polar bear population (300 bears)

enters the market each year from Inuit hunting (Rode 2010).

Polar bear attacks on humans are rare. In almost all cases, the polar bear in question was

undernourished, frightened, or provoked.

Hundreds of polar bears gather near Churchill,

Manitoba, every fall to wait for the sea ice to form

on Hudson Bay. Yet since 1717, only two

townspeople have ever been killed by polar bears.

Scientists expect human polar bear-encounters to

increase as the sea ice continues to melt and

hungry bears are driven ashore (Rosing 2006).

Over the past few years, sea ice losses have led to

more polar bear sightings in northern coastal

communities and an increase in human-polar bear

encounters (Rosing 2006).

Fig 10. A surveyor, was returning to his car in the

remote town of Barrow, Alaska, when he saw the

polar bear

"About Polar Bears." Polar Bears International. N.p., n.d. Web. 11 May 2014.

<http://www.polarbearsinternational.org/about-polar-bears>.

Mulvaney, Kieran. The Great White Bear: A Natural and Unnatural History of the Polar

Bear. Boston: Houghton Mifflin Harcourt, 2011. Print.

Rode, Karyn D. "Reduced Body Size and Cub Recruitment in Polar Bears Associated

with Sea Ice Decline." Ecological Applications 20.3 (2010): 768-82. JSTOR.

Web. 11 May 2014.

<http://www.jstor.org/stable/10.2307/27797845?ref=search-

gateway:1798895f30c8b9c5926b7c139ec07fed>.

Rosing, Norbert. The World of the Polar Bear. Richmond Hill, Ont.: Firefly, 2006. Print.

Stirling, Ian. Polar Bears: The Natural History of a Threatened Species. Markham, Ont.:

Fitzhenry & Whiteside, 2011. Print.

Images

Fig 1. Photograph by Jessica Robertson, USGS, taken September 29, 2008.

Fig 2. Stirling, Ian. Polar Bears: The Natural History of a Threatened Species. Markham,

Ont.: Fitzhenry & Whiteside, 2011. Print.

Fig 3. polarbearsinternational.org

Fig 4.http://wwf.panda.org/what_we_do/where_we_work/arctic/wildlife/polar_bear/diet/

Fig 5. http://www.polarbearsinternational.org/about-polar-bears/essentials/hunting-and-

eating

Fig 6. http://www.dailymail.co.uk/news/article-2049475/Awe-inspiring-breathtaking-

pictures-life-survival-melting-polar-worlds-again.html

Fig 7. Stirling, Ian. Polar Bears: The Natural History of a Threatened Species. Markham,

Ont.: Fitzhenry & Whiteside, 2011. Print.

Fig 8. http://footage.shutterstock.com/clip-6192440-stock-footage-polar-bear-ursus-

maritimus-cub-playing-outside-the-den.html

Fig 9. http://www.nwf.org/wildlife/wildlife-library/mammals/polar-bear.aspx

Fig 10. http://www.dailymail.co.uk/news/article-1102347/Chilling-game-hide-seek-

hungry-polar-bear.html

Fig 1. Polar bear on sea ice in the Beaufort Sea near Barrow, Alaska,

near the end of a U.S.-Canadian research cruise. Photograph by Jessica

Robertson, USGS, taken September 29, 2008.