根据国际自然保护联盟（International Union for Conservation of Nature）的数据，目前大约有17,800种动物处于“濒危”（Endangered）状态，即有较大的灭绝风险。除了少数例外，绝大多数濒危动物的处境都是由人类活动造成的：人类正在扩大自己的活动范围，不惜侵犯它们的栖息地，推平一片土地并在上面建造各类设施；为了满足私欲而偷猎和过度捕猎；以及正在改变全球气候和动物迁徙模式的全球变暖……人类活动对动物的伤害固然严重，但我们也不必过度悲观。今天就让我们走进动物保护工作者的日常，看看他们如何通过科学的方法将物种从濒临灭绝的悬崖边缘拉回。
首先出场的是一种大家都熟悉且喜爱的动物：大熊猫。2024年10月，两只大熊猫，宝力和青宝，从中国飞抵美国华盛顿哥伦比亚特区的史密森学会国家动物园，开启为期约十年的异国生活。皮埃尔·科米佐利（Pierre Comizzoli）是美国史密森学会国家动物园和生物保护研究所（Smithsonian’s National Zoo and Conservation Biology Institute）的研究兽医，负责探索野生动物生育力保存（fertility preservation）和辅助生殖的前沿技术。他介绍道，大熊猫是一种非常独特的生物。它们与其他熊类动物虽同属食肉目熊科，但在经历了漫长的演化后，我们今天在动物园里看到的熊猫通常只爱憨态可掬地啃竹子，吃肉反而是罕见的情况。这是因为大熊猫的野外栖息地位于中国的青藏高原东缘至秦岭山脉一带，这里分布着面积广大的竹林，却少有便于大熊猫捕捉和食用的动物。而大熊猫选择了适应环境：吃竹子。近几十年来，随着中国中部的开发步伐加快，大片竹林遭到砍伐，野生大熊猫的数量也随之下降，仅剩一千余只。故事的转折点发生在1972年，中国将大熊猫玲玲（雌）和兴兴（雄）作为友谊大使赠送给美国，美方决定将其安置在史密森学会国家动物园，此后的五十余年间，这里一直是中国旅美大熊猫的居住地。大熊猫的到来吸引了来自世界各地的数百万粉丝来到动物园参观，也为美国动物护理人员和野生动物学家提供了宝贵的探索机会。他们除了研究大熊猫的生命活动、健康状态和繁殖过程，更深入地了解大熊猫的发情、交配、受孕、假怀孕和幼崽发育等繁殖行为，还与中国学者和大熊猫饲养员建立联系、开展合作，中方动物园的繁育、兽医和生态研究为大熊猫的人文关怀管理提供了关键数据。他们共同调查大熊猫在中国的原生栖息地，为野生种群保护提供了宝贵的见解。时至今日，中美大熊猫国际保护合作已经改变了它们的处境。大熊猫野外种群总量从20世纪80年代的约1100只增长到近1900只。在大熊猫人工繁育方面，按照优化繁育配对方案，2023年全年繁育成活大熊猫46只，全球大熊猫圈养数量达728只。经科学评估，现有大熊猫圈养种群保持90%遗传多样性的时间可达200年，成为健康、有活力、可持续发展的种群。世界自然保护联盟也已将大熊猫的受威胁等级由“濒危”调整为“易危”。在所有保护工作中，最为艰巨的任务当属为圈养大熊猫进行人工繁育。玲玲和兴兴在美国生活的20年里，诞下的5只幼崽都在出生几天后夭折。大熊猫的野外繁殖成功率较低，为了恢复野生种群，人为干预是必要且迫切的。但在当时，没人知道它们为什么难以繁衍后代。这种情况一直持续到 21世纪初，不同的野生动物研究机构开始共享信息并开展合作，试图找出问题所在。皮埃尔表示，当时的美国境内仅有一对大熊猫，仅凭两只个体并不足以全面分析出一个物种的生物学特性。要想了解它们在营养、兽医护理和繁殖监测方面的真正需求，就必须前往它们的故乡，中国，在那里针对更多个体开展更全面的研究。研究人员当时已经知道，大熊猫的繁殖期每年只有一次，通常在3月到5月之间。进一步调查显示，在这三个月的繁殖期里还存在一个更短暂的窗口期。雌性大熊猫在整个繁殖期内确实会通过激素等信息吸引雄性，但能保证它们之间成功交配并受孕的时间窗口最多大概24~72小时。皮埃尔和同事确定了雌性大熊猫在繁殖期内的受孕窗口，在精确的时机将一对大熊猫放在一起，期待它们碰撞出爱的火花，最终成功怀孕并生育幼崽。2000年，中国又向史密森学会国家动物园借出了一对大熊猫“美香”（雌）和“添添”（雄）。这两只大熊猫之间的化学反应有所不同。它们表现出相互喜欢的良好迹象，并为短暂的繁殖期做好了交配准备。但不幸的是，它们似乎不太擅长此事，在繁殖过程中花费了过多时间调整姿势……[查看全文]
Conservation Efforts Are Bringing Pandas, Wolves and Panthers Back from the Brink
Rachel Feltman: If I asked you to guess how many animal species are threatened with extinction right now, would you have a number in your head? Is it hundreds, thousands?
Feltman: Well, according to the International Union for Conservation of Nature, it’s about 17,800 of them.
While there are a few exceptions, almost every animal species that’s on the threatened list is there because of human activity. We’re clearing land and building stuff over their habitats, we’re poaching and overhunting, global warming is shifting temperatures and migration patterns—I could go on and on. But instead, let’s talk about how we humans are using science to help bring some species back from the brink of extinction.
For Scientific American’s Science Quickly, this is Rachel Feltman. To finish up our four-part series about conservation science, which we’re calling “The New Conservationists,” we’re talking about our favorite kinds of animal stories: the comebacks!
Our guide for this adventure is Ashleigh Papp, an animal scientist turned storyteller. And for this episode, she’ll take us to Washington, D.C., where just this past fall two fuzzy new VIPs arrived from China. (I’ll give you a hint: they’re black and white and adorable all over.)
This decades-long collaboration between researchers in the U.S. and China has quite literally turned the tide for one charismatic species in particular.
Pierre Comizzoli: Pandas are kind of magic, and in terms of evolution they are so unique because they are carnivores originally, you know, like any other bears, but they evolved very differently.
Ashleigh Papp: That’s Pierre Comizzoli. He’s a research veterinarian with the Smithsonian’s National Zoo and Conservation Biology Institute.
Comizzoli: They started, really, to eat bamboo to survive and to modify their diet, and, well, they don’t eat only bamboo; they also eat some small animals—but this is fantastic, how a species got really adapted to a very specific environment, which is the bamboo forest in central China.
Papp: Long ago central China had bamboo aplenty, which worked really well for the adapted pandas. But many of those bamboo forests have been cleared for development in more recent decades. As a result panda numbers have dwindled.
In 1972, when wild panda populations were hovering around 1,000, First Lady Patricia Nixon mentioned that she really loved pandas at a dinner in Beijing. Important government officials were at the table, and soon after China offered two pandas, one male and one female, to the American people. The Nixons decided that the Smithsonian’s National Zoo in Washington, D.C., would be the perfect home for them.
[CLIP: Patricia Nixon speaking about the pandas arriving at the National Zoo: “On behalf of the people of the United States, I am pleased to be here and accept the precious gift of the panda—pandas and also these other mementos from the government of the People’s Republic of China.”]
Papp: The new arrivals drew huge crowds. The zoo staff members were hoping to learn more about the pandas in captivity to help regrow the wild population. But answers turned out to be elusive. In the 20 or so years that the pandas lived at the zoo they produced five offspring, but none of the animals lived past a few days.
And it wasn’t just a problem in D.C. Everyone was experiencing a similar panda babymaking issue, which continued into the early 2000s, when Pierre joined the National Zoo team. Around then different institutions started sharing notes and collaborating to see if they could figure out what was going wrong.
Comizzoli: Only one pair of animal is not necessarily enough to understand the full spectrum of the biology of a species. And going to China was very important, because there was access to many more animals. And, of course, as you can imagine, you know, individuals are not necessarily similar. So there was the possibility to study a lot of animals and to understand what was really the needs in terms of nutrition, in terms of veterinary care and in terms of monitoring of the reproduction.
Papp: Researchers already knew that the breeding window for giant pandas is only open one time each year, usually from March to May. But what they later figured out, through their own research and a lot of collaboration, is that within the three months of opportunity, there’s an even smaller window.
Comizzoli: The female is not necessarily able to conceive during the whole breeding season. She can attract a male, but there is a very short window of time when the female can breed with the male and then conceive.
Papp: That very short window is about 24 to 72 hours maximum.
[CLIP: “None of My Business,” by Arthur Benson]
Papp: Once Pierre and his colleagues defined the female panda’s conception window within the breeding season, they needed to figure out the precise right time to bring the two pandas together and let sparks fly.
Comizzoli: What is the optimal time to put the male and the female together to make sure that there would be a successful breeding, leading then after that to a pregnancy and a baby.
Papp: In 2000 China sent over two more pandas on loan to the National Zoo. And the chemistry between these two was different.
Comizzoli: They really showed all the good signs that they liked each other, that they were ready to breed during this very short breeding season. Unfortunately, they were not really experts, and they were spending way too much time to try to adjust, you know, their positions...[full transcript]
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