Our Planet II’s closing note, and David Attenborough’s plea for us to do more to save the natural world

There is a jarring, emotionally wrenching moment toward the end of Our Planet II’s fourth and final hour that is bound to upset most, if not all, viewers.

It is doubly jarring because — spoiler alert — what happens is not, on the face of it, the direct result of human impact on the world’s wildlife migrations, a recurring theme throughout the series. One could be forgiven for thinking it belongs in a different program, one with a less lofty goal than what Our Planet purports to be.

In the end, this final hour of Our Planet II, The Freedom to Move, feels hurried and rushed, and not at the level of the other episodes in the program. It does have its moments, though.

And the important, overriding message remains the same.

Through our actions as a species, we are despoiling the home we live in, and it will take an act of real will and perseverance to put nature back into the natural world. Restoring the natural balance to our increasingly troubled world will not come easily, and it remains to be seen whether we have the collective ambition and ability to do the right thing.

Once again, the hour focuses on three months in the planetary cycle, in this case, the months of January through March, when large groups of animals from the equatorial south begin their arduous, annual trek north. Gentoo penguins in Antarctica are shown feeding their chicks in the brief southern summer, so they can grow strong enough to undergo their first voyage to the sea, where leopard seals, known for their voracious appetites, lie in wait. Human detritus is in evidence even here, in the most remote corner of the Earth. Penguin parents do not have it easy at the best of times, and these are not the best of times.

Snow geese from Loess Bluffs, Missouri, take to the skies in large numbers — the first time this mass migration has been filmed from above, using drones — while far away, on the other side of the continent, pronghorn antelope from southern Wyoming make their way through mountain passes and fenced-in ranchlands to the relative comfort and safety of Grand Teton National Park.

Army ants in the Amazon Rainforest enter their migratory phase in which the queen and her supersized larvae swarm over long distances in the dark of night. In another first, Our Planet’s film crew captured the nighttime migration using infrared lighting, and the results are both eerie and eye-filling.

Freedom to Move’s pièce de résistance is the annual grey whale migration from the warm but food-depleted waters off Baja California to the rich feeding grounds of Alaska’s Bering Sea, where king crab, Bristol Bay salmon, and innumerable groundfish coexist in a complex but little understood web of life. The grey whale migration alone was more than a year in the making, and it’s clear there’s enough here to warrant an entire series in its own right.

The whale migrations are tougher than at any time in recorded memory, as the whales, including mothers and their young calves, navigate some of the busiest shipping lanes in the world, and pods of predatory orcas lie in wait off Monterey Bay. The year of filming witnessed the lowest number of calves born in Baja since 1994, and the overall number of migrating whales was down 40% from previous years.

As always, though, it is David Attenborough’s distinctive, evocative voice that lingers long afterward, and gives Our Planet its sense of purpose.

“For many animals, the instinct to move is overwhelming, despite the dangers,” Attenborough reminds us at the end, as if viewers need another reminder of what’s at stake in the race against extinction. “We have … changed the planet, cutting off ancestral routes, and impacting even the most remote corners of the globe. There is hope. We know more about these journeys than ever before. And with our help, many animals are now overcoming the challenges of our modern world.”

But are they? For a healthy and connected planet, we must preserve, as Attenborough puts it, the freedom to move.