The number of women serving time in New Zealand prisons has jumped by almost one-third in three years and prison staff say the inmates are younger and more violent.
A leading researcher partly blames the media, as young girls grow up trying to mimic the violent "kick-ass" women celebrated in video games and on television.
Figures released to the Sunday Star-Times show that from 2009 to 2011 the number of female prisoners increased by 27 per cent, from 437 to 555.
Of the 19 prisons in New Zealand, three in Auckland, Wellington and Christchurch are specifically for women.
The prisons have a security classification system and three years ago, for the first time, a maximum security category was introduced.
Last year the average female prisoner was serving a three-year sentence for an offence involving violence, drugs, antisocial behaviour, alcohol, dishonesty or their driver's licence.
Around 16 per cent claimed to have gang affiliations, almost two-thirds identified themselves as Maori, 31.5 per cent European, 4.8 per cent Pacific and 3.8 per cent Asian.
The Department of Corrections said many had mental health, drug and alcohol issues and histories of abuse and trauma. Typically they were also unemployed and had a low level of education.
Christchurch Women's prison manager Wayne McKnight said a lot had changed in the nearly 11 years he'd been involved with the prison.
"When I first came here we had 37 prisoners and there weren't too many young ones amongst that," he said.
"This year we will have around 85 to 90 prisoners [and] we're getting a lot more younger ones in now for violent offences ... and so a lot more aggravated burglaries, robberies, assaults ... the whole lot."
McKnight said he'd formed the opinion that the shift had something to do with police adopting a zero tolerance approach and more female judges.
"Perhaps a male judge might have been a little more lenient with females," he said.
Figures obtained by the Star-Times show that a quarter of the 268 judges serving in New Zealand courts are now women, with 57 the average age of all judges in the employment, environment and district courts.
Nelson-based social anthropologist Dr Donna Swift said there had been a rise in the level of violence attributed to women.
Last year there were stories of young girls brutally attacking female classmates and last week the issue hit the headlines again when a pregnant 24-year-old woman was hospitalised after being dragged from a Rotorua shop, punched and kicked by a young woman. The attack happened during the day, in front of people waiting for buses.
"We've always had tough girls, gang girls, girls that were from the other side of the street – but now [violence] is glorified and now it's something that people talk about, now it's seen as cool," Swift said.
Young women were moving into new territory "cracking beer bottles over someone's head and that kind of thing – that's more common than it used to be".
Canada and America had also seen a jump in female prisoner numbers, she said.
Swift said the reason was a combination of society no longer tolerating behaviour it would have "laughed off as a catfight" and harsher penalties for a "breach of female etiquette".
"It's really entrenched in our society that girls are sweet, and nice and kind and when they step over the line, we come down pretty hard on them."
The opposite was true in popular movies, television shows and video games where violent but "drop-dead gorgeous" lead female characters, who were more concerned about getting their message across than who they hurt along the way, were celebrated.
Late last year Swift released findings from her two-year study into why girls engage in violent and antisocial behaviour.
The reasons included building a reputation, fighting to "keep their man" and defending themselves against physical or emotional harm and alcohol.
For some girls who hadn't done well at school or didn't have parents turning up to their netball games, uploading a video of themselves fighting on to social media was one way of getting "a little bit of self-validation".
Swift said most girls hit 15 or 16 and "get over it, get on with their lives". Those that didn't were the ones that ended up in prison.
- Sunday Star Times