Elizabeth Hunt Burrett, a mother from Australia, experienced a moment with an orangutan while breast-feeding her son at Melbourne Zoo last year.

As she tells it, the orangutan came over to watch, locked eyes with her and gave an affirming nod. “It was the most beautiful thing,” she wrote in a widely circulated Facebook post.

While it may be impossible to know exactly what this orangutan was thinking, it’s true that the critically endangered apes are exceptionally dedicated mothers. They give birth to one baby at a time, raising each for six to nine years, until it’s time to rear another. Mother and young sleep and spend most of their time with only each other. And young orangutans nurse longer than any other mammal — sometimes into their ninth year of life, according to a study published in Science Advances on Wednesday.