The chart shows that the number of babies being born in America has increased pretty dramatically since the 1970s, and that the number of males and females born is generally about even.

Most interestingly, it shows that a significantly higher proportion of babies are born in the summer months. For both sexes and most years, July, August and September are the darkest colored squares, while the fall and winter are much lighter. Counting back nine months, I guess we know how couples were passing the winter.