Seasonal abundance of four species of Micrurus in Southern and Southeastern Brazil was inferred from collection data for eight years at the Instituto Butantan, São Paulo, Brazil. For most species surface activity was significantly lower during drier and colder periods. Low temperature may considerably reduce snake metabolic rates and consequently constrain their activity. Year-round availability of prey may explain this activity pattern as well. Reproductive condition (duration of vitellogenesis and mating) may also influence activity patterns and explain some differences among species. One species (M. corallinus) shows vitellogenesis and mating restricted to the first half of the rainy season (spring), when activity peaked. Field data and activity patterns indicate that mating occurs from the end of the rainy season to the first half of the dry season (in autumn) in the other three species (M. altirostris, M. frontalis, M. lemniscatus), which belong to the same clade, and this sets them apart of M. corallinus. The data obtained here indicate that differential reproductive strategies occur in two distinct clades of Micrurus.