Spotter K.C. Namgyal at work

Immediately before the BBC Earth team arrived, nine cats had been spotted in 12 days, so the signs were promising. Anderson had assembled a large team, reasoning that to get good footage he needed ample time in the field and a team big enough to cover all the angles. Before they left, the team trained in mountain rescue and avalanche safety in the Rocky Mountains of Idaho, US. With three camera operators, two assistants, and 11 local guides, spotters, porters and support staff, the shoot in Ladakh took six weeks. Anderson was excited about filming snow leopards, but also nervous. "They are still incredibly rare, incredibly elusive, and it's a hard place to work with the altitude and weather," he says. As a result, his first sighting was a memorable experience. He looked through the telescope and saw a snow leopard over a kilometre away. “It wasn't the best quality sighting that you can ever imagine, but it was just so exciting,” he says. "It was an amazing moment," says Anderson, "one that I'll always remember."

Hints of the grey ghost of the mountains through a scope

One of the lead camera operators was John Shier of 45 North Films, who has a reputation for capturing spectacular footage of large animals and difficult habitats. He had already worked on big cats, having filmed North American pumas, but the project was his first trip to India, first foray into the Himalayas, and first opportunity to sight a snow leopard. "My first impression was that it was a very beautiful place, with a warm culture," says Shier. "The other thing I noticed right away was that ecotourism is gaining a strong foothold." In North America, visitors to national parks are familiar with the phenomenon of a "bear jam". In Hemis, says Shier, there were snow leopard jams, with 20 to 30 tourists crowding around on the trail, trying to see the cats. So the BBC crew trekked "to places the tourists don’t normally go to," says Shier. It paid off: the crew spotted five cats in their first five days.

Tourist season in Hemis National Park

For camera operator Mateo Willis, arriving in Ladakh stirred a flood of memories. On previous family treks to the region he had constantly scanned for snow leopards, but only caught a couple of fleeting glimpses. "Literally a pinprick in binoculars," he says. Returning to the region was the realisation of a dream. Doing so also came with risks, one of which was potentially fatal altitude sickness. The team landed at over 3500m in Leh, and their filming location in Rumbak was another 500m higher. At that altitude, it is not recommended to ascend more than 500m per day. They took four rest days upon arrival at base camp, "to really slowly work ourselves up into peak condition so we could be tracking the cats all over the mountains," says Anderson. They took oxygen and a depressurisation chamber. Being so remote, they were unlikely to get rescued by helicopter if there was an emergency. Each day, the entire team did a questionnaire to watch for signs and symptoms of altitude sickness. "No matter how many times you've visited high-elevation locations," says Willis, "there is always an element of uncertainty." Fortunately, there were no medical incidents, no bad storms, and very little snow. However lighting conditions were a challenge. Light bounced around a lot, reflecting from the pale rock. Heat and ultra violet radiation were also a problem. Sometimes, says Anderson, "we were desperate for shade."

The dry, cold peaks of Ladakh