Birth seasonality in the early Spanish-Mexican colonists of California (1769-1898)

The pattern of birth seasonality in California's early Spanish-Mexican colo nists between 1769 and 1898 was reconstructed using genealogical data for p rogeny of 657 marriages. The monthly distribution of the 3824 births in thi s sample shows a strong seasonal pattern, with spring and fall peaks (corre sponding to peaks in conceptions during July and February) and a low point in October. This seasonal reproductive pattern is the result of a complicat ed set of interactions among environmental, physiological, and cultural var iables. California's strongly developed winter rainfall pattern and the 19t h-century agricultural cycle clearly influenced the seasonal pattern of mar riages and births in this agrarian society. Several historical processes in teracted with these environmental and economic factors to transform the sea sonal birth pattern of the early colonists. Through time the birth pattern becomes less variable and the birth maximum shifts from spring to early win ter. This appears to be, at least in part, a result of changes in labor pat terns and an increase in average parity. These data suggest a multifactoria l explanation for birth seasonality, in which the timing of conceptions and births is influenced by both environmental and socioeconomic factors.