What are the stages of maturity for a bear?
- cub: a juvenile still being cared for by its mother (e.g., feeding and defense against enemies; possibly play).
- subadult: sexually immature juvenile, but independent of direct care by the mother. Rarely associates with its mother.
- adult: sexually mature – i.e., post-pubescent
- adolescent: post-pubescent, but immature behaviorally and physically
- prime: fully mature behaviorally and physically
- senior = senescent: so old that physical condition is declining
What are boars and sows?
Historically, these terms may have first been applied to swine, where boar = adult male, and sow = adult female. Somehow these
terms were also applied to bears. People who do not know swine well consider that demeaning to bears and prefer just referring to
“adult males” vs. “adult females.” However, people familiar with the intelligence of swine, and the similarities of their diets to those of
bears, tend to accept using the same terms for both swine and bears.
What does it mean that a female is “in season”?
- This is another way of saying that a female is physiologically and psychologically prepared to mate.
- Preheat (= pre-estrus): During this phase, eggs begin ripening in her ovaries. She produces scent that attracts males. She
travels widely, creating a scent trail for males to follow. She does this by dribbling urine containing hormones revealing that
she is in season. Once males find and court her, the eggs continue ripening.
- Mate competition: As multiple males are attracted to a female, the males compete among themselves for opportunities to
mate with her.
- Heat (=estrus): During heat (= estrus) itself, she mates. The act of mating causes release of her eggs – a process known as
induced ovulation. The eggs move down her fallopian tubes where they may be fertilized.
- Delayed implantation: Before or after fertilization, eggs finish their trip down the fallopian tubes. Each fallopian tube (the right
and left) connects to the corresponding branch (i.e,. “horn”) of the Y-shaped uterus. It is in these horns that the embryos may
implant and begin growing at the onset of hibernation in fall. Meanwhile, the embryos remain in a kind of suspended
animation – a phenomenon known as “delayed implantation.”
- Mate choice: Females have some choice in which males they mate with. So males who win rank battles aren’t necessarily
the only ones or even the first ones who mate. But domination can increase likelihood of being able to mate and sire cubs;
losers have little opportunity. As a general rule, adolescent males usually lose to prime adult boars. However, exceptions
occur, for instance once the prime boars have exhausted themselves or are too busy fighting to mate. Or the adolescent male
might find a receptive female that prime males have overlooked.
- Pseudo-estrus (= false estrus) There is evidence that a female’s first pre-estrus and estrus occur the year before she is
actually mature enough to have a full estrus. During her first pre-estrus, she doesn’t attract prime adult boars, but can attract
adolescent males who will court her. This allows adolescent males to practice courtship without having to compete with a
prime adult male that might seriously injure or kill it. It also allows a female to learn about courtship before being confronted
by a prime adult male that won’t take “no” – or even “not quite yet” – for an answer. If the female mates, she doesn’t get
pregnant – hence the term “pseudo” estrus.
What are the mating seasons for bears?
Females have a narrower season than males do.
- Black and grizzly bears: mid-May – mid-July is most common, although some mating may still occur during August. A female
in estrus during late July or August is most likely to be in her first estrus or pseudoestrus.
- Polar bears: mate about 1 month earlier – i.e., mid-April to mid-June. Because of this overlap in mating seasons between
grizzly and polar bears, male grizzly bears sometimes end up mating with female polar bears. The reverse almost never
occurs because male polar bears are normally far from shore, out on the sea ice. during the grizzly bear mating season.
How and why do bears court? How do they mate?
Courtship serves three functions
- It assures that a females eggs do not ripen until there are males present to fertilize them. Once eggs are ripe, they have a
“shelf life” of only a day or two before they begin deteriorating.
- It gives a female some choice in which male(s) she mates with.
- It teaches the female that she can trust the male to get close to her in this circumstance. Under any other circumstances,
allowing a male within touching distance, to say nothing of allowing one to climb onto her back, could be inviting disaster.
Prime adult males are sometimes highly aggressive and irritable, and have been known to kill and eat other bears.
Courtship begins: with one or more males following a pre-estrus female. This can go on for several days.Males will approach her,
lick her vulva and/or taste her urine stream to detect hormones indicating that she has entered estrus. Until that happens, any attempt
by a male to mount her is discouraged as she sits down, covering her vulva; or she may threat or even bite or swat the male.
From there on, there are three patterns of courtship:
- Romantic: During courtship and perhaps between matings, the male and female play extensively. The female tries to mate
only with this suitor. In some cases, they have been friends for months or years before this mating. (Uncommon).
- Mutual lust: Courtship involves little play as well as ritualized aggression such as gape-mouth displays by both male and
female as they stand head-to-head. Once estrus occurs, the female may simple stand still and allow a male to mate –
sometimes several males in succession. (Typical).
- Forced (rape?): Male skips courtship and forces a female to mate, for instance by biting her in the neck until she submits.
(Uncommon)
How do bears compete for mates?
- Female competition: As females lay down scent trails, one might say that they are competing to attract males. But no one has
yet detected anything else females do to attract males, much less to deter other females.
- Male competition: Males compete by intimidating one another or, occasionally, by fighting. Most fights last less than 10
seconds and do relatively little damage. Rarely, however, one male seriously injures or kills a rival – especially one that
refused to submit.
At which ages do males and females reproduce?
Initial reproduction: The better bears are nourished, the faster they mature and the larger they grow. Within each species, larger the
average body size of bears, the younger the age at which they begin reproducing.
- Black bears: Highly nourished females are first impregnated at age 3 and first given birth (i.e., whelp) at age 4. Poorly
nourished females don’t whelp until age 6.
- Grizzly bears: Even those that are well nourished seldom whelp before age 9. Poorly nourished ones (e.g., on Alaska’s North
Slope) don’t whelp until age 10.
Final reproduction: Better-nourished mothers also tend to produce cubs until older ages. However, even the best-nourished sows of
all 3 species seldom produce cubs after age 20.
When does gestation occur? When are cubs born?
Implantation of embryos is delayed until a female enters her winter den. If she is fat enough to produce cubs, the embryos implant in
her uterus and begin developing. Gestation lasts 2 months (i.e. about 60 days)
- Grizzly and black bears, implantation normally occurs in late November, followed by birth in late January.
- Polar bears, implantation and birth occur about one month earlier – just as mating season does.
What are the roles of adult males and females in caring for cubs?
- Males: Their primary role is siring cubs. Their secondary role is sometimes to limit the number of other prime males
inhabiting an area. By actively promoting emigration by locally-born males and by discouraging immigration by distantly-born
males, a male reduces the competition he must face each day. Also, males sometimes kill cubs that they did not sire.
- Females: The mother provides all direct care of cubs before they become independent. After independence, he offspring may
be allowed to continue sharing her home range for one or more years. Because they have learned where food, shelter and
hazards can be found in her home range, they an use it efficiently. They also benefit from her reducing local competition from
other families.
What is the typical sex ratio of cubs at birth?
- Black & grizzly bears: 55%♂♂ vs. 45% ♀♀
- Polar bears: 50%♂♂ vs. 50% ♀♀
How is the ability of a juvenile to survive on its own related to its age?
Age matters less than maturity. The better nourished a cub, the faster it grows and matures – i.e., the sooner it can separate from its
mother and the earlier the age it will it will complete puberty.
Ability to survive independently increases as a cub matures, being zero during the first months after birth while still in the den and for a
few months thereafter. In many habitats, no more than half the mother-reared cubs survive their first year; and of those fewer than
90% may survive their second year. Bears orphaned at less than 9 months old almost never survive in the wild.
Age at which cubs are weaned?
Cubs of course start nursing immediately after bear. They may continue doing so until they dissociate from their mother permanently,
except while hibernating. Suckling resumes the following spring and may continue until the cub becomes independent of its mother,
although some cubs are weaned while still with the mother.
At which age do they become independent of their mother?
Most cubs become independent during a mating season, when their mother comes into heat again for the first time since their birth.
(Lactating females rarely come into heat). Some cubs separate at their own initiative; others are driven away by the mother or by her
suitors. Keeping cubs away from lusty boars minimizes risk that they will be injured or killed by a boar.
- Black bears: cubs typically become independent during the 2nd mating season after birth – i.e., at an average age of roughly
15 months. However, in habitat where nutrition is especially poor, cub maturation can be so retarded that they do not become
independent for another year – i.e., at ~27 months old.
- Grizzly bears: In any given population, some cubs may be weaned during the 2nd mating season after birth (~15 mo old). But
most are not weaned until the 3rd (~27 mo old) or 4th mating season (~39 mo). However, slow-maturing cubs, may not be
weaned until the 5th mating season (51 mo). The fastest maturation occurs in populations where abundant salmon provides
a wealth of nutrition – for instance in some parts of SE Alaska, Kodiak Island, or the Alaska Peninsula. The slowest maturation
occurs on the barren grounds near the Arctic Ocean.
- Polar bears: Most become independent during the 3rd or 4th mating season after their birth.
What is a subadult?
- Independence: Once a bear has separated from its mother, it is known as a subadult (= pre adolescent).
- Females tend to share their mother’s home range for several years, if not life-long. Or they establish their
own home range near mom’s. So most females in an area tend to be related to one another.
- Males usually remain on their mother’s home range for only a year or two before emigrating, sometimes
traveling hundreds of miles before they establish a home range.
What distinguishes an adolescent from a subadult or from an adult?
Subadulthood ends and adulthood begins with puberty. The first stage of sexual maturity is adolescence. The second stage is prime
adulthood. The final stage is senescence.
How many cubs are born in a litter? How often are litters born?
The better a female’s level of nutrition, the higher her reproductive rate. The earlier the age at which she first bears cubs and the larger
her litters.
- Black bears: Most single-cub litters are born by first-time mothers that are poorly nourished. Older and/or better nourished
mothers are more likely to produce 2-3 cubs. Exceptionally-well nourished mothers can produce up to 6 cubs per litter.
Because cubs are typically cared for until the 2nd mating period of their lives (around age 15 mo), a mother who successfully
raises at least one cub from her litter will normally produced cubs only every other year. However, if all cubs in a litter die
before the litter is 5-6 mo old, the mother might give birth again just 1 year after the doomed litter was born.
- Grizzly and polar bears: First-time or poorly nourished mothers usually produce 2 cubs. More mature and/or bGetter
nourished mothers commonly produce 3 cubs. Exceptionally well nourished grizzly bear mothers produce 4 cubs. There are
been 1 or 2 reports of a 5-cub litter, but that might have been enlarged by adoption. No reports yet of a polar bear with 4 cubs.
Do bears adopt orphans?
Grizzly bears: occasionally
- Mixups: If the cubs of sow A start wrestling with the cubs of sow B, all the cubs transfer their scent to one another until all smell
pretty much alike, such that the two mothers cannot tell whose cubs are whose. If the cubs do not separate and return to their
own mother voluntarily, all the cubs – including those of the subordinate sow – may leave with the dominant sow when she
leaves, in which case they have been adopted, in effect. Whether they adoptees stay with her long term isn’t known.
- Orphans: some are adopted, but not many.
Black bears: Adoption is less common because cubs become independent 1-2 years earlier than grizzly bear cubs. When cubs are
orphaned during the first months after birth, while hibernation is underway, the orphans are sometimes put into a den with a mother
that already has cubs. To keep her from rejecting the foundlings, Vicks vaporrub is put on her nostrils so that she cannot smell the
foundlings until they have come to smell like her cubs and herself.
Polar bears: Few, if any, documented cases of adoption.
How long do bears typically live?
- In the wild, about half the bears born survive until adulthood.
- In habitats where most bears die because of human hazards (e.g., shot by someone or hit by a vehicle) most males are dead
by age 12 and most females by age 16.
- In habitats relatively free of human hazards, bears tend to liver roughly 4-5 years longer.
- The oldest bears of all 3 species found in the wild have been in their late 20’s or early 30’s. A few captives have lived into their
40’s.
Bears fill some of the same ecological niches in the northern hemisphere that apes do in the southern hemisphere. The fact that
both tend to be semi-arboreal forest-dwelling omnivores has led to parallel evolution in several ways. Both taxa have binocular color
vision, large brains, high manual dexterity, similar limb morphology, and similar ways of walking and of standing on their hind limbs
(bipedal plantigrade locomotion). Furthermore, both apes and bears have prolonged parental care and are generally black in color.
Interestingly, the only non-black ape, the orangutan, is also the only ape that shares its habitat with a bear -- the sun bear.
Furthermore, whereas chimpanzees, bonobos, and gorillas are highly social, the orangutan is no more social than bears. BVA
researcher Stephen Stringham and his Malaysian colleague Siew-Te Wong are investigating similarities and differences between
sun bears and orangutans in an effort to understand why they are not either more similar or more different. The bear least like apes
is, of course, the polar bear, which lives on the sea ice and eats little but meat. They are also the least social bears.
How smart are bears compared to those great apes?
Bears are approximately as smart as a great apes. In captivity bears learn some things faster or retain memories longer than a
apes. In the wild, they are similarly clever in meeting the challenges of daily life. In fact they solve some problems in virtually the same
ways.
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