Feeling the heat?: substantial variation in temperatures does not affect the proportion of males born in Australia

The global proportion of male births has been shown to vary with climate, with a higher proportion of male births documented in colder climates. Here we examined the hypothesis that ambient temperature predicts fluctuations in the proportion of male births in Australia and within seven Australian states using historical annual data spanning 1910-2009. We predicted that within states with tropical ambient temperatures the proportion of male births would decrease when ambient temperatures are higher. First, considering the national composite births for the whole of Australia, the proportion of males born ranged only from 0.510 to 0.517. We observed no relationship between the proportion of male births and the mean annual temperature in the concurrent or previous years for Australia as a whole. Second, the analyses for the seven Australian regions provided a total of 14 estimated relationships. We found no association between ambient temperature in the previous or concurrent year and the proportion of males born for all 14 comparisons. Thus, we found no evidence of a negative relationship between ambient temperatures in the concurrent or previous year and the proportion of males born in the tropical regions of Australia, and no evidence of any relationship in the more temperate Australian regions or in Australia as a whole