Do Australians have a mating season?

With around 26 million inhabitants and only 365 days in a year (usually), you’d think the spread of birth dates in Australia would be pretty even.

But you’d be wrong.

The Australian Bureau of Statistics (ABS) has compiled some fascinating data on birth dates over the last 10 years and ranked them from most common to least common.

The analysis reveals some interesting patterns.

The top five most common birthdays in Australia in order are: 17 September, 8 April, 23-24 September and 1 October.

The five least common are: 26 January, 1 January, 25-26 December and 29 February .

Four out of five of the least common dates are public holidays, which is not surprising since more 35 per cent of births in Australia are by caesarean section and have a certain degree of predictability.

Doctors don’t usually book c-sections on public holidays.

But interestingly four of the top five dates are all clustered around a two-week period from the middle of September to early October.

Read: Most popular baby names in Australia since 1950

The New Daily  has done some further digging into these numbers, counting backwards from this period 280 days (or 40 weeks) and revealing that these babies were most likely conceived in late December.

This probably doesn’t sound like much of a surprise, with the end of the calendar year traditionally a holiday time when people are relaxed and at ease around Australia. But the end of year festivities may not be the main driver here.

Data visualisation group Visme has created a heatmap based on global birth date data compiled by the United Nations, with birth date data plotted against geographic data – specifically the latitudinal and longitudinal points of the births.  

Plotting the data in this way reveals that the peak days and months for births across the world follow a north-south pattern, which seems to be influenced by the weather. The peak birth period in the far northern hemisphere is across their summer months of July, August and September.

Read: How your birth order affects you

“As you move down the list of countries, ordered from highest to lowest latitude, you can clearly observe that the peak birth months shift farther and farther to the right, occurring later in the year,” Visme notes.

“Once you’ve entered the middle latitudes, or the tropical zone, September and October become the highest-ranking months by average number of live births per day, followed by November and December, with some spilling over into the next year.”

Or, to clarify, the further from the equator you are the more likely you are to conceive in colder months and give birth in summer.

Move closer to the equator and the opposite is true, with the data skewing toward summer conceptions and winter births. Humans, wherever they are, seem to have an ideal conception temperature, rather than a specific ‘mating’ period.

Read: How, why and where we’re growing

Research published in the scientific journal Human Reproduction also backs this up.

“The ideal time of the year to conceive is when the sun is out for 12 hours and the temperature is between 50 and 70 degrees Fahrenheit. For reasons not totally understood, these are the perfect conditions for conception, either because they stimulate sperm production or ovulation – or a combination of both,” it states.

This all tracks closely with the ABS findings, with December traditionally being one of the warmer months.

It seems the nice weather, in combination with the festive atmosphere (and probably more than a little alcohol) and the holiday period, provides the perfect environment for making babies.

Do you share any of the most common birthdays? How about the least common? Let us know in the comments section below.

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Written by Brad Lockyer