In low‐ and middle‐income countries, significant differences in fertility beliefs between rural and urban areas arise from the differential timing and pace of fertility declines. Demographers have long hypothesized about the diffusion of these beliefs and behaviors from urban to rural areas, potentially via temporary rural–urban labor migration. In this paper, we investigate the association between temporary internal migration from rural Senegal to the capital city, Dakar, and differences in the fertility and contraceptive beliefs and preferences of migrants and nonmigrants. We test socialization, selection, and adaptation hypotheses by comparing the fertility ideation of current and returning migrants with that of nonmigrants and future migrants from their place of origin. Our results support selection effects, explaining half of the differences between nonmigrants and migrants. Once selection effects are removed, significant differences remain between nonmigrants and current or returning migrants. These differences are largely explained by two complementary measures of adaptation: years lived in Dakar and the number of ties to residents of that city. The results indicate that adaptation is as important, if not more so than selection in explaining differences between migrants and nonmigrants. This holds true even for returned migrants five years after their last migration spell. Of the two potential adaptation mechanisms explored, the time spent in Dakar generally explained adaptation better than ties to nonmigrants in Dakar. However, our complementary analyses do not rule out the importance of urban networks on fertility, as they contribute to migrant selection.