If expectant mothers think they're wealthy, researchers think they'll more likely have a son.
Researchers already knew girls are more resilient in the womb and in early life and had theorised that better maternal conditions resulted in a boost to males births.
But Australian National University researchers have suggested perception has a bigger impact than reality.
They found Australia is bucking the trend of industrialised nations such as Canada and the UK where the proportion of boys being born is declining.
Canberra appears to be behind it all.
Biological anthropologist Alison Behie said ACT's birth rate of 110 boys to every 100 girls is dragging Australia's numbers above the global trend for other industrialised countries of 105 to 100.
"Our research shows this may come from perception," Dr Behie said in a statement on Thursday.
"Having the perception of prosperity is potentially more important than actually having the money or resources."
A range of maternal characteristics such as age, education, income and weight was analysed but only wealth perception proved to be a reliable predictor of birth sex.
The study looked at 5000 births across Australia over 12 years and was published in the Journal of Biosocial Science.
