Tracking down the Casady sisters was never going to be easy. They’ve been on the road since they were small – and barely stopped.

“The road is not for everybody, but for us it’s natural,” explains Sierra, who is first on the phone in the south of France when we finally catch up.

“We find a real sense of home and stability on the road. It is normally something that sustains and rejuvenates us. It has a kind of magic.”

Born in Iowa and Hawaii, Sierra and Bianca moved around the western states of the US with their artist mother and shamanistic father, who taught in Steiner Waldorf schools.

By the time they hit their teens the duo were independent – not just from their parents but from each other. Their mother had taken them out of school completely because she thought there was more to be learnt doing art in the real world than in school.

“We had a tumultuous and erratic childhood,” explains the louder, younger of the two, Bianca, when the phone is passed over.

“It had some beautiful phases and some dark phases. Our mother definitely struggled a lot. We were too young to even remember, but there was a lot of stress and danger in our early childhood.”

Their father left when they were young, but only after taking them on spirit-ual vision quests in the desert, often without food. His absence often figures in their music, not least because they like to be isolated, to reject outside influence.

“We have a lot of mental illness in our family, so there is a sense of not having been seen or recognised by our father, which can be a painful experience. But I think our experience has a lot of vagaries, in terms of levels of abuse and abandonment.”

Bianca “Coco” and Sierra “Rosie” (two years senior) moved to New York, separately, as teenagers. At that point, they had no contact.

Sierra later moved to Paris to study opera at the Conservatoire de Paris. Bianca, who studied linguistics and sociology in New York, joined her in the French capital ten years ago, when they formed CocoRosie.

“We had this intense instinct to develop our independence from our family and that included divorcing ourselves from each other.

“We came together more whole people, though. Did we know where the other one was? I don’t know if we even really cared.”

Yet, Sierra says, “they are not plugged into the world”.

“I’m not a huge music listener and I don’t study art either. So it is interesting to see where I have come from. I had a very eccentric father who taught us Native American-style drumming as children.

“That brought us something interesting – I can’t say what but I fell in love with opera because of the committed discipline one must have in order to explore that.”

Earlier this year she worked on Soul Life, a small, experimental, “dreamy and moody” operetta of six movements, which premiered in Austria.

“Most of the time people think of opera as a discipline that shuts down creative forces but there is something interesting about the composed music one surrenders to.”

They are arty and intense but never cloying. While Sierra worked on the opera, Bianca formed a magazine: GAG (Girls Against God). Sierra had come up with the name on a rollerblading trip through New York.

“It had a weight to it so we both knew it was going to be something. I bought the website before we knew what it was about. I can’t remember what happened next.”

The answer is she loved an article sent to her by artist Anne Sherwood Pundyk and turned it into a magazine aiming to “resist and reinvent”. It was launched in London at an event in response to the arrest of Russian punk band Pussy Riot.

“It’s not anti-spiritual. It’s against thousands of years of male leaders who have plagued us.”

Both have found theatre a great form of expression this year. They helped turn Peter Pan into a musical for adults with eccentric American playwright Robert Wilson and the Berliner Ensemble in April (there are more European dates at Christmas).

Intuition

“We got together every day for 40 days and did these 15-hour sessions in the dark, creating through experiment. The style of development is unique and radical and suited us well. It is all based on intuition and spontaneity, turning off the brain and turning on something else, which is incredible.”

Their fifth collection as CocoRosie arrived in May. For Tales Of A Grass Widow, Bianca and Sierra invited regular contributor and friend Antony Hegarty into their home as they sat around singing and playing the harp.

They later flew to Iceland to “reconnect with something primal, natural, which was the adventure of the second half of the record” and circled back to ideas from their earlier records with plenty of beat-boxing and severe beats, which keeps tweeness at bay.

The cover art is an abandoned child.

“For me the role of art is not to make a statement that is fixed,” says Bianca. “It is to create something to live; it has to be mutable and timeless, so I’m always curious to see how people react to the image.

“There’s something about an abandoned child that’s dark, but I also feel like it is a really common part of the human experience: as an adult we learn to cover up wounds, and we manifest our personalities around them, but Bianca and I are open to investigation of those wounds.

“It has always been there in our work but we have been particularly journeying back in time – and we can assist each other in that. We have a completely different set of memories, so we are helping each other pencil in the blanks, because there are a lot of blanks…”