Civil unions have proved to be almost as durable as traditional marriages in the first seven years since the legal status was introduced.
Statistics New Zealand figures provided to the Herald show that 4.4 per cent of civil unions registered in New Zealand from 2005 to the end of 2009 were dissolved by the end of last year, compared with 3.8 per cent of marriages in the same period.
The actual numbers - 82 civil unions dissolved out of 1876 - were so small that Statistics NZ demographer Anne Howard said any differences with the rate of marriage breakdown were unreliable.
Massey University Associate Professor Mark Henrickson, who leads a research project on New Zealand's gay, lesbian and bisexual communities, said the figures were no surprise.
"The percentages look close enough to say I don't think there is a difference between the civil union and marriage populations, which is not terribly surprising if people go to the effort [to formalise their relationships]," he said.
Family First lobbyist Bob McCoskrie, who opposed legalising civil unions in 2005, agreed.
"Humans are humans and conflict happens no matter what the sexuality of the relationship," he said.
Figures released yesterday show that 377 couples entered civil unions last year - 168 female couples, 133 male couples and 76 heterosexual couples.
Discounting couples who were living overseas, civil unions have held steady for the past five years at between 1.3 per cent and 1.5 per cent of all marriages and civil unions of New Zealand residents.
Same-sex civil unions represented only 0.9 per cent to 1.2 per cent of all marriages and civil unions, lower than the 3.9 per cent of young males and 4.7 per cent of females who said they were attracted to the same or both sexes in a survey of 9100 secondary school students in 2007.
Dr Henrickson said the low take-up was because while gay, lesbian and bisexual people wanted the legal right to formalise their relationships, few actually wanted to sign up to civil unions themselves.
"It's about equality in society rather than specifically undertaking the rite or the ceremony," he said.
A survey of 2200 gay, lesbian and bisexual people in 2004, just before civil unions were legalised, found that 64 per cent wanted to formalise their relationships eventually.
The low take-up of civil unions in practice matches a long-term decline in the rate of traditional marriage, from a peak of 45.5 marriages for every 1000 unmarried adults aged 16 and over in 1971 to an historic low of just 11.8 last year.
Only 69 per cent of all partnered adults aged 25 to 44 were legally married at the last census in 2006.
Statistics NZ said the declining marriage rate reflected the long-term growth of de facto unions, more people staying single, and later marriage. The average age at first marriage has risen from 23 in 1971 to 29.9 years last year for men, and from 20.8 to 28.3 for women.
However, those who do marry are slightly more likely to stay together than they were a generation ago. The divorce rate has dropped from an average of about 12 a year for every 1000 existing marriages in the late 1980s to 9.8 last year, the lowest since divorce laws were liberalised in 1980.
The median length of marriages ending in divorce has lengthened slowly, but consistently, from a low of 11.9 years in 1990 to 13.7 last year.
But the proportion of marriages ending in divorce within 25 years has risen consistently from 29 per cent of couples who married in 1971 to 35 per cent of those married in 1986.