Seasonal migration and seasonal variation in fecundability: effects on birth rates and birth intervals.

Seasonal patterns in conception rates have been documented in several recent studies. In this paper, a mathematical model of the reproductive process is developed through which the impact of such variation in conception rates is assessed. It is found that the effect on fertility can be quite substantial, but that the birth rate when seasonal variation is occurring is approximated well by the birth rate calculated when conception rates are constant at their mean. These results indicate that further documentation of seasonality in conception rates and exploration of the causes of these patterns and their change is an important area for demographic research.