Bears forgo a lot of activities to conserve their energy in the winter when food is
在食物短缺的冬天 为保存能量 熊不再进行许多生命活动
scarce – even important bodily functions like eating, and peeing, and pooping.
甚至一些重要的机体功能 如进食 排泄都被摒弃
But they aren’t just saving energy for an extra-long nap –
they also give birth during hibernation. Yeah, bears have their babies while they’re
在冬眠期 它们还会生崽 没错 冬天藏窝里
tucked away in their dens for the winter!
This seems like it would be the harshest possible time of year
一年里 在这个时间段生崽 似乎再艰难不过
for cubs to be born, especially when they’re pretty much stuck inside.
So how and why does that happen?
Hibernation is a state of inactivity that many warm-blooded animals,
like bears, enter for several months out of the year.
But contrary to popular belief, this physiological state isn’t just a
really long sleep when the temperatures drop.
Instead, it’s an extended period of torpor – a state of reduced activity that is
相反 该状态为延长的休眠期 即处于不利环境及
triggered in adverse environments and during periods of food scarcity.
During torpor, an animal’s metabolism, breathing,
在休眠期 动物的代谢减慢 呼吸变缓
and heart rate slow down and its body decreases temperature.
Animals can go in and out of torpor daily or it can last for several days,
weeks, or months, at which point it’s referred to as hibernation.
数周或数月 如为后者 即被称作冬眠状态
Some researchers have called bears super hibernators because their body
temperatures only drop a few degrees, in contrast with smaller hibernators like
squirrels, whose body temperatures drop to near freezing.
Because they don’t have to unthaw themselves,
bears can react to any potential threats really quickly.
And even if they look like they’re sleeping,
bears are still aware of their surroundings.
A paper published in 2011 reported that black bear heart rates increased as soon
as researchers approached their dens,
indicating the bears could detect the potential danger outside.
They also found that pregnant black bears’ heart rates increased as their
pregnancy progressed, and the bears moved even less once the babies arrived,
心率也随之加快 而幼崽一出生 母熊甚至会减慢移动速度
to probably avoid accidentally crushing them.
When the babies are first born, they only
require warmth and a constant supply of milk.
As long as the female has adequately prepared before hibernation,
she can provide for both herself and the cubs.
To do that, bears have to build up a massive fat store in order
to survive several months of hibernation.
Their bodies slowly metabolize those fat stores to use as a food and water source.
Their bodies even turn waste products into proteins to keep their
muscles and essential organs functioning properly.
And the success of a female bear’s pregnancy is tightly
linked to those fat stores.
That’s because bears are one of several mammals
whose bodies delay pregnancy until conditions are right.
After mating takes place in the spring or early summer,
the fertilized embryo hangs around, waiting to implant in the uterine wall in the fall
but only if the female has enough stored fat.
For example, researchers have found that brown bears with less than
举个例子 研究者已发现 体内脂肪少于20%的棕熊
twenty percent body fat didn’t get pregnant even when mating had occurred.
This may have evolved as a way to protect female bears from expending energy
that they don’t have since they have to use their fat reserves as
both fuel for themselves and their cubs.
As weird as it sounds for them to go to these lengths to give birth
during the months when food is hardest to find,
there are some good reasons that this works for them.
This strategy allows bears to spend all their time foraging for
food when it’s most abundant, without pausing to give birth.
And the babies are protected in the den when they’re most vulnerable to predators.
So when a bear emerges from the den with little cubs who are seeing the sky for
the very first time, they weren’t just lazily hanging out inside –
a ton of preparation and energy went into bringing them safely into the world!
在跟着熊出窝时 有生以来第一次看见天空 得以安全来到世上
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