Why does it seem like every year, as soon as the weather begins to warm up, women start having babies all over the place? Along with blooming flowers and lengthening days, it always feels like warm weather brings on the babies. When I was in grade school, as soon as spring arrived it seemed like someone was bringing in a birthday treat every week. Now, as a woman in my twenties, I have three friends who have given birth in the past two months alone … and there’s still a lot of summer left.
About four million babies are born in the United States every year, and interestingly, a disproportionate number of them are born during warm weather. According to the Centers For Disease Control, more babies arrive in the summer than any other season, and July, August, and September are the most common months for infant births in this country, with August hosting the most births out of any month of the year and February consistently having the smallest number.
Why Warm Weather?
In the animal kingdom, spring is a time when many species come out of hibernation and begin to breed … and give birth. Animals time their fertility and gestation to coincide with the best weather, because young born during the warm season will have a better chance of surviving. They’ll have more food sources, they’ll have lots of fresh water, and they are less likely to die of exposure. Animal mothers prefer to give birth during spring and summer because those seasons make it easier to provide for a whole litter. It’s hard to imagine a nest of duck eggs surviving during a snowstorm, or a hutch of bunnies learning to find food in the cold. Animals know that warm weather ensures their young’s survival.
In temperate zones of the Northern hemisphere, the birthing season for most animals runs from about April to September, but in the Southern hemisphere, it’s the opposite. Animals down under have their babies in December and January, since those are the mildest months for them. In places like Africa or South America where conditions are often dry and barren, animals give birth to their young to coincide with the rainy season, when food and resources abound. Even animals that live in the harshest climates time their birthing season to coincide with the best weather. Baby penguins in Antarctica hatch just in time to catch a brief bit of sunshine.
At one point in our evolution, humans may have followed this general rule, too. Back when we were hunters and gatherers, it would have made sense to give birth while conditions were mild. Obviously, though, living in cities and in commercial societies has taken away some of the threats that early humans faced. Women can now give birth to a baby at any time of year and be reasonably sure that they can provide for it.
Since food and shelter aren’t a question anymore, sociologists look at human behavior to try to decipher why so many babies are born in July and August, and that means going back nine months to when the babies were conceived. Full-term babies born in the summer were conceived during fall and winter. Some anthropologists theorize that more babies are conceived during the winter because that’s when people spend more time together indoors. Babies born during the winter would have to be conceived in milder weather, when people are more likely to be spending time active and outdoors. However, spring is the next most common season for births, and since babies born in the spring were conceived during the summer and fall, this theory might not adequately explain all conceptions and births. Some demographers believe that summer is popular because many women, especially teachers, purposely time their births to coincide with summer vacations or lenient vacation policies.
Does the Economy Cause a Baby Boom?
Researchers know that besides weather, cultural factors also contribute to the fluctuating birthrate. Birthrates are consistently highest during times of economic boom, and they’re lowest during recessions and depressions, such as the market downturns of 1972, 1982, and 2001. During the Great Depression, birthrates fell by about 26 percent, and the Gulf Coast experienced significant declines after Hurricane Katrina. On the other hand, a record number of babies were born in the United States at the height of the economic boom in 2007. Since the current slowdown set in, the birthrate has been slowing again.
Although some rumors of purported baby booms that follow weather events and disasters might be urban legends (like the myth of a baby boom following the 2003 New York City blackout), sometimes freak occurrences can have a measurable effect on births. Colorado experienced an unusually high number of births in September of 2007 that demographers traced back to a powerful blizzard that hit the state around Christmas of 2006. While stuck in their houses with no power and no transportation for many days, couples in Denver and Boulder spent plenty of quality time together.
Beside specific months or seasons, most babies choose to enter the world mid-week. According to the U.S. Census Bureau, more babies are born on Tuesday and Wednesday than any other day, and Sunday is the slowest day of the week. This may be because of the prevalence of scheduled labor and cesarean sections, which take place only during the week. Statisticians also know that for a variety of reasons, births of boys outnumber births of girls.
Since so many factors influence our fertility and reproductive behavior, and much has changed since our hunter-gatherer days, it’s hard to tell exactly why so many babies are still born during the balmy summer and spring months. But no matter when they arrive, modern moms can be sure that babies born in any season, on any day, have the same chance of leading happy, healthy lives.