Thanks to massive conservation efforts and tens of millions of dollars spent over the last 40 years, humans are probably the only reason giant pandas haven’t gone extinct yet.    Of course -- as we take up more and more of its native habitat in China -- we’re also the reason that they’re in trouble in the first place.    So, saving them seems like the least we could do.   And our efforts seem to be working, sort of -- there are about 1,600 giant pandas living in the wild today and another 300 in zoos around the world.   But pandas present a conservation challenge like no other.    Giant pandas have one of the strangest and most perplexing diets in the animal kingdom, and they’re equally unusual when it comes to reproduction.   We can help with both of these things when the animals are in captivity, but it raises the question …. how do pandas manage to exist in the wild?   Let’s start with the food. You know that pandas eat bamboo, but did you know that it makes up to 99 percent of their diet?   This would make total sense if pandas were a kind of herbivore, but they are in fact a type of bear.    Instead of having complicated, fermenting four-chambered stomachs like cows, their digestive systems resemble those of carnivores, with a simple stomach and short small intestine. So, giant pandas actually can eat meat…. they just don’t.   When scientists sequenced the panda genome in 2009, they found that the bears don’t even have the necessary genes for making enzymes to break down all the cellulose in bamboo.   As a result, giant pandas have to eat between 9 and 18 kilograms of bamboo every day.   It also means wild giant pandas spend as much as 16 hours a day foraging and eating, leaving the rest of the day mostly for sleeping.   But it’s not like they’re being picky eaters. It’s likely that pandas weren’t always so reliant on bamboo. But as ancient humans arrived into their territory, they moved to higher elevations and started eating bamboo to avoid competing with other meat eaters.   And it’s only now that scientists are beginning to understand how giant pandas can survive on this weird, finicky diet.   Researchers tracked three male and three female giant pandas over the course of six years, looking closely at what they ate in their natural habitat in China’s Qinling Mountains.    Of special interest was the amount of nitrogen, phosphorous and calcium they ate, since those are the most important nutrients for mammals.   It turned out that pandas tweak their tastes for bamboo, from one part of the plant to another, and one species to another, as the year progresses.   A lot of their diet consists of a certain type of bamboo called wood bamboo, and throughout the year, the pandas go from eating the leaves of the plant, to the shoots, which contain more phosphorus and nitrogen.    But as the shoots grow, they lose those nutrients -- so the pandas move to higher elevations and switch to eating the shoots of another bamboo species, called arrow bamboo.    Then in mid-summer they switch yet again, turning their attention the leaves of the arrow bamboo, which have lots of calcium.    By late summer, the females return to the lower elevations to give birth, at which point they switch back to the leaves of the wood bamboo.    It’s all very complicated, and what’s worse, this poor diet also makes reproduction -- which is notoriously challenging to begin with -- even harder.   Though pandas can reproduce when they’re as young as 4 to as old as 20, female giant pandas only ovulate once a year, in the spring.    The window during which they can conceive is usually between one and three days. So rabbits they are not.   Then, if a female manages to become impregnated in the spring, the embryo stays in a state of arrested development known as delayed implantation.    Researchers think the embryo only re-starts its development after the female returns to lower elevations and can eat more of the calcium-rich leaves of arrow bamboo -- nutrients she needs for fetal bone growth and lactation.   But again, because of the bears’ inconsistent and nutrient-poor diet, newborn pandas are far from giant.    Famously described as the “size of a stick of butter,” infant pandas usually weigh between 90 and 130 grams, less than a third the weight of other bear cubs.   So, if being cute has given them the evolutionary advantage of making us want to take care of them, all I can say is, well, played pandas. Well played.   And on behalf of humanity, I should say sorry for making things harder for you guys.    But also … you’re welcome.   Thank you for watching this SciShow Dose, which was brought to in large part by our SciShow President of Space, Chris! Thank you Chris for your support and encouragement! If you would like to be a President of Space, you can go to Patreon.com/scishow to learn how you can support this channel, and get monthly rewards in the process.