The air is thin and we have to rest several times on the shore hike from camp. To our left, snow-covered mountains disappear into clouds that seem almost close enough to touch. On the plain in front of us, we can just make out a herd of graceful animals. This is why we stay here.

Tibetan antelopes live mainly on the plains of Tibet. Watching them move slowly across the green grass, I'm struck by their beauty. I'm also reminded of the danger they are in. They are being hunted illegally for their valuable fur.

My guide is Zhaxi, a villager from Changtang. He works at the Changtang National Nature Reserve. The reserve is a safe place for the animals and plants of northwestern Tibet. To Zhaxi, protecting the wildlife is a way of life. “We're not trying to save the animals,” he says. “Actually, we're trying to save ourselves.”

In the 1980s and 1990s the population of Tibetan antelopes dropped by more than 50 percent. Hunters were shooting antelopes to make money. Their living places were becoming smaller as new roads and railways were built.

In order to save Tibetan antelopes, the Chinese government placed them under national protection. Zhaxi and volunteers watched over the antelopes day and night to keep them safe from attacks. Bridges and gates were added to let the antelopes move easily and keep them safe from cars and trains.

The measures were effective. The antelope population has recovered and in June 2015, the Tibetan antelope was removed from the endangered species list. The government, however, does not intend to stop the protection program since the threat to the Tibetan antelope has not yet disappeared. Only when we learn to exist in harmony with nature can we stop being a threat to wildlife and to our planet.

Yellow fever began to spread in Brazil in 2016, severely threatening the golden lion tamarin, a little monkey living in the rainforest of southeastern Brazil, whose population was small even before the outbreak. So, scientists created a vaccine (疫苗) to protect the monkeys. But, it is a new idea to vaccinate animals. Historically, conservationists have believed that humans should not interfere directly with wildlife. A traditional saying in the world of conservation work is “Leave it as is.”

However, Tony Goldberg, a scientist and animal doctor at the University of Wisconsin-Madison, believes in vaccinating wild animals when possible. “Some people say we shouldn’t touch nature. But really, there are no unspoiled natural habitats left.” he said . “This epidemic moved very quickly from north to south, across the country — no wildlife does that. It’s people. They cross vast distances in buses, trains, planes. They bring the disease with them. We realized that in five years, we could lose the entire population if we did nothing.”

The vaccine led to antibodies in the tested monkeys and caused no harm, the scientists found. So far, about 300 have been vaccinated and are reported to be doing well. Tests show that more than 90 percent of the monkeys have immunity or resistance to the virus since vaccination.

The outbreak of yellow fever is no longer a big problem for the monkeys, and their population is starting to come back. But even with the success of the vaccine program, scientists are still not sure about creating vaccines for other animals. Jacob Negrey, a biologist who studies monkeys, wondered about unpredictable effects of such wildlife treatment. He explained that you might create a treatment that helps one kind of animal but hurts another.

We were at the top of the mountain when the call came through on the radio.

I was in the Altai Mountains with Biosphere Expeditions(生物圈考察队) as a member of the first team to take part in a survey of snow leopards(雪豹) in this part of the world.

Getting to the base camp had been an expedition in itself. It was getting dark as we arrived. After a very welcome night’s sleep we were up early for a couple of days training on how to fill in the datasheets, identify tracks and prints and what to do with useful animal droppings amongst other things.

The next day four of us set off up one of the mountains to do our first surveying with our guide Oleg. We spent most of the morning climbing the endlessly steep mountain with little communication from Oleg who only became active when we stopped to take on water. By early afternoon we reached what appeared to be the top but was another ridge(山脊). My 47-year-old bones were shaking and I was struggling to breathe. We hadn’t seen a thing except for rocky mountains. Our guide was keeping going but we had very little idea about what we were supposed to be doing. Energy was dropping rapidly.

Then everything changed. The radio came to life. Hardly able to speak through excitement, one of the other groups told us that they had just discovered fresh snow leopard tracks!

On arrival, we found the other group silently looking a gulf(溪谷). A set of very clear paw prints ran from top to bottom. I was filled with a feeling of complete exhilaration. One of the rarest big cats in the world had passed through where I was standing! They were here and what we were going to do would help them survive.

All the suffering of the past days fell away. The long walk back to the base camp that night seemed to go by in seconds.