What is the largest species of penguin?

The emperor, up to about 1.2 metres and 40 kilograms, and the only animal that breeds through the Antarctic winter. The males stand for around 65 days in temperatures to minus 50 with the egg on their feet under a fold of skin, eating nothing, huddling in colonies that rotate individuals from the freezing edge to the warm centre and back.

The huddle is genuinely collective. Thermal imaging shows it behaving like a fluid, with small movements propagating in waves through thousands of birds so that everyone spends time inside, and the interior reaching temperatures above freezing while the outside is at minus forty. Nobody is organising it; it emerges from each bird shuffling towards warmth.

They dive deeper and longer than any other bird - over 500 metres and beyond twenty minutes - by slowing the heart, collapsing the lungs and tolerating oxygen levels that would render a human unconscious. Their colonies are now counted from space by the stain their guano leaves on the ice, which is how several previously unknown ones were found, and how the losses are being tracked as the fast ice they breed on becomes less reliable.