They would have been aided in this by the advent of the pill and the legalising of abortion,but their motives would have had a lot to do with the higher levels of education being attained by women,and by those women's desire to get established in their career - and maybe in home ownership - before starting a family.
This trend to delay child-bearing continued until the early 2000s,since when it's started to reverse. My guess is that the earlier trend went a little too far,and is now being corrected. If so,we could expect the fertility rate soon to stabilise rather than continue rising.
Nobody knows with any certainty why these shifts occur,but the demographers offer two main theories.
But first,understand this. For decades,surveys of young women have shown that the great majority of them intend to have two kids. About one in five say they don't intend to have kids,but these are offset by the small number saying they'd like to have more than two. This finding implies that what varies is not couples'views on the desirable number of kids,but the context in which they find themselves,particularly their economic context.
So the first theory says couples have been starting their families earlier in recent years because economic conditions have been more conducive. It's been easier for young people to get jobs,there's been less worry about keeping your job,interest rates have been manageable,and there's been an atmosphere of optimism about the economy's prospects. (This optimism departed during the relatively brief period when we feared we'd be swept up in the global financial crisis,so it's possible that births in 2009 will experience a temporary dip.)
This is the right context in which to acknowledge that the introduction of the baby bonus - along with the Howard government's repeated increases in family payments and its 30 per cent child-care tax rebate - may well have contributed to couples'confidence that economic conditions were favourable for child-bearing.
The second,supplementary theory is that all the public discussion of the plight of women who left it too late to have children may have encouraged more women to get on with it. If so,the trend to earlier starts may lead tomore children being born because fewer women find they've left it too late to fit in a second kid. (The median age of women having children is now 30.8 years.)
But I don't think those of us who worry about Australia's population growing by more than the natural environment (let alone dysfunctional state governments) can cope with need be too worried about the rising birth rate.
It remains to be seen whether the fertility rate will continue rising even to the long-term steady-state level of 2.1 babies per woman,let alone exceed it.
No,it's not natural increase that will do us in,it's high levels of immigration. And it's much more effective and easier politically for governments to control the immigration intake than to cut back the supposed monetary incentives to have kids. The policy lesson for governments from the new baby boom is that a sustained rise in the fertility rate is a much more effective way to alleviate the problem of an ageing population than is ramping up immigration.