Recently, a keeper was walking past the great ape house at the Smithsonian National Zoo, in

Washington DC, when he heard whistling coming from inside. Thinking that one of the zoo’s visitors had infiltrated the restricted area, he hurried to investigate. It turned out not

to be a person who was making the noise, but one of the ape house’s long-time residents, Bonnie, a 30-year-old orang-utan.

Bonnie’s new trick has sent ripples of excitement through the world of primatology, where it has been a long-cherished assumption that orang-utans can’t whistle.

Serge Wich and his colleagues at the Great Ape Trust in Des Moines, Iowa, think she copied it from the keepers and have been studying Bonnie’s behaviour since she went public. She can’t hold a tune, as such, and in the scientists’ opinion she doesn’t whistle for attention, or to ask for anything, but just to pass the time of day.

“It appears that she does it for her own satisfaction,” says Al Setka, a spokesman for the trust.

Wich says it shows that orang-utans can learn new sounds, which might mean that different populations in the wild have different vocal cultures.

That won’t be news to Dutch primatologist Carel van Schaik, who has recorded the sounds wild orang-utans make while going about their business.

While one population Van Schaik has studied is fond of making smacking sounds while nest-building, for instance, another prefers to blow raspberries.

Bonnie has a reputation as an early adopter.

When, some years ago, the zoo installed an elevated system of towers and cables that connects the ape house to another facility where the orang-utans take part in memory and language experiments, she was the first to test it.

“As with humans, there are certain individuals who try things out more,” Wich says. “They are very important as agents to get innovation started in a population.”

When another orang-utan in the ape house was also observed whistling, the keepers couldn’t be sure if she had also copied them, or if she had copied Bonnie. But one thing is certain, says Wich: “The whistle in Washington spread.”