Trinley Norbu has honed his climbing skills, long the key to successful courtship for men in the small matrilineal Zhaba ethnic group of Sichuan province

Nimble after years of practice, Trinley Norbu is used to hoisting himself three stories up the side of a stone house and through the window for a one-night stand in his southwest China community.

While other young men squire their love interests to dinner or a movie, Norbu has honed his climbing skills, long the key to successful courtship for men in the small matrilineal Zhaba ethnic group of Sichuan province.

The Zhaba eschew monogamous relationships for traditional "walking marriages" -- so-called since men typically walk to their rendezvous before slipping through their lover's window.

But the 37-year-old truck driver and others in the remote area on the edge of the Tibetan plateau lament that the tradition is waning, as women increasingly want a bit more commitment from a man.

The arrival of the internet, smartphones, livestreaming and popular Korean TV shows, along with improved transportation and education opportunities beyond the valley, have exposed the once isolated Zhaba to other lifestyles.

"Now the women especially have begun to want the same things as outsiders -- fixed marriages, and financial assets such as a house or car," he said.

But an even more dramatic challenge looms on the horizon: one of the world's tallest dams will soon flood the valley, forcing villagers to scatter as they relocate from ancestral homes.

"It's heartbreaking. They've turned our area upside down, and we don't have any say in it," said Trinley Norbu, who is temporarily employed by the construction site.

His friend Khando Tsering stared up at the towering, unfinished support pillars of a highway that will soon halve travel times to the nearest city -- and bring tourism to the once-pristine enclave.

"The economy will develop and people's character will degenerate. Everything will be about money, and our local traditions will disappear," he predicted.

"That's just how things work in this era."

- 'People as possessions' -

Walking marriages began disappearing in the 1980s as the government imposed strict family planning measures.

The new policy meant heavy fines for babies born without legal fathers, forcing Zhaba people to obtain government marriage certificates and identify -- on paper at least -- a single partner as a spouse.

That process introduced the idea of "people as possessions" and caused a rise in notions of jealousy, an emotion once rarely overtly expressed, according to a paper by Qinghai Normal University anthropologist Feng Min.

Since then, walking marriage has become less and less common. Feng's 2004 survey of 232 households found that only 49 percent of Zhaba households still practiced the tradition.

Children in such families are raised by their mother and her siblings in large, six-storey communal houses of yellowed stone on the lush green hillsides, with cavernous rooms too large for much light to penetrate.

Fathers might provide some financial support, but live with their mother.

"I don't have a husband. Their father lives somewhere else," said 60-year-old matriarch Dolma Lhamo after a breakfast of yak butter tea and tsampa, roasted flour eaten by hand, as she led two daughters out to tend the family potato field.

Shopkeeper Pema Bazhu used to share a home with her mother, grandmother, sisters and uncles, but she recently chose to move out and live separately with her husband and two year-old son.

"It's much more common now to see families living on their own as a unit," she said. "It's more convenient, and it's better for raising children."

- 'If she's willing' -

Tsultrim Paldzone, 30, explained that when he and his friends were younger, they would snag tokens from girls they fancied on festival or market days, calling cards to be returned that evening during a nocturnal visit to her home.

"If she's willing, then she'll run just a little bit less fast. If she's really not willing, you won't grab that token no matter how hard you try to steal it," he laughed.

Cars were uncommon then. He had once walked over 10 kilometres (six miles) to reach one lover's home, starting before sunset and arriving after midnight.

Now no one in the small community – just some 13,624 people according to the latest 2010 census - lives more than a half hour's motorbike trip away.

Trysts are arranged ahead of time on the popular cellphone messaging app WeChat, and the coy game of token-grabbing has mostly disappeared.

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