Among the many achievements of the BBC Natural History Unit, the 2006 series, Planet Earth, stands tallest. A landmark in nature programming, it won innumerable awards, spawned a big screen offshoot (2007's Earth) and is the benchmark against which all other nature programmes are measured.
Or rather, it was the benchmark, because 10 years after Planet Earth, the BBC has made an even more ambitious follow-up, Planet Earth II.
Mike Gunton, an executive producer of Planet Earth II, says the pressure to top the most acclaimed nature documentary series in the history of television weighed heavily.
"In some ways, it's not even the reality, it's the legend," Gunton tells Weekend in Los Angeles. "No matter how good the first one was or how good the second one was, the worry was people would say 'The first one was like the Ten Commandments or something'."
Gunton says he and his team breathed a large sigh of relief when the initial trailer for Planet Earth II was received rapturously -- but the real turning point for the series came when a particular sequence from the first episode was released online and went explosively viral.
A heart-stopping beach chase involving a plucky little marine iguana and a raft of hungry snakes, the clip showed animal behaviour that had never been captured on camera before and contained more thrills than a dozen Hollywood action movie climaxes.
"When I first saw it I just thought 'This is a once in a generation sequence'," says Gunton.
One of the ways in which Planet Earth II manages to up the ante on its predecessor is via the use of portable, miniaturised film-making technologies that didn't exist when the first series was made. It makes for a much more intimate experience with the animals.
"It's about proximity -- getting the camera as close as possible, as close as is comfortable, to see that behaviour," says Gunton. "Whereas Planet Earth 1 was obvserving the world, Planet Earth II is experiencing the world. But it's still the same stories. There are habitats -- how do animals cope with the changes of the habitats? But rather than observing how they cope, this is about experiencing with them how they cope."
Each of Planet Earth II's six episodes features a variety of locations under the umbrella of a single topographical theme, such as Islands, Mountains, Jungles and Cities. The stunning birdlife of the New Zealand Subantarctic Islands features in episode one. Considering the extreme breadth of wildlife examined in the series, Weekend asks Gunton how they go about choosing what to shoot.
"The research phases are incredibly exciting but also nerve-racking," he says. "You can't just go on Wikipedia. You've got scientists and field workers and camera teams -- it's quite an organic network of information. You're looking for a balance of the types of animals, the types of emotional storytelling."
The most identifiable throughline across both series is narrator/presenter David Attenborough, the face and voice of BBC's Natural History for generations.
Although Attenborough's advanced age prevents him from participating in the often perilous location shoots, Gunton is emphatic that the series represents the famous naturalist's values.
"He's not physically there, but his influence is all-pervasive," says Gunton. "I've worked with him for over 30 years and so whenever I do one of these projects, I'm always thinking in my head: How would he tell this? How would he frame that story? Where would that structure go? He's there sort of in spirit, that sounds very New Age, but it's absolutely true."
Gunton seems in genuine awe of Attenborough's ability to provoke an emotional response via his narration.
"The writing of the scripts is obviously a collaborative effort, but the performance of it is pure Attenborough. It's something that people probably can't imagine but it is like watching a virtuoso musician, because he does it in one take. There are very very few flubs.
"So it's like a live performance, and that's why I think people get so engaged with him because you feel he is there with you, telling you that story, sitting next to you."
Planet Earth II premieres on Sunday, July 9 at 7.30pm on Prime.