The changes appear to be due to male-dominated emigration to Australia, females doing better in education, and women's roles as "cultural connectors" who run local marae, organise family events and keep in touch with relatives.
After a 90-year gap, Censuses have collected iwi affiliations again only since 1991. Since then the ratio of men to women in our biggest iwi, Ngāpuhi, has dropped from 96:100 to 88:100.
Dr Kukutai has previously shown that Māori have migrated to Australia at a faster rate than other New Zealanders this century, lifting the Māori share of the NZ-born population in Australia from 13.8 per cent in 2001 to 17.1 per cent a decade later.
Even by 2001, more Māori men than women were emigrating in all working age groups. Males made up 50.8 per cent of the Māori population in NZ under age 20, but only 47.2 per cent of Māori still here aged 20 to 59.
By 2013 males were still 51 per cent of the Māori population in NZ under 20 but only 45.9 per cent of Māori still here in the working age groups.
Dr Kukutai said another factor was a shift in tertiary students from mainly male to female, possibly affecting numbers learning te reo Māori.
The last elderly generation of native Māori speakers is dying fast, down from 51 per cent of people aged 60-plus in 2001 to 34 per cent today.
The numbers of Māori speakers under age 20 have dropped sharply - from 25 per cent of girls and 21.2 per cent of boys in 2001 to 19.6 per cent of girls and 17.2 per cent of boys in 2013.