Nestling survival may be an important factor driving population fluctuations of arvicoline rodents, yet few data exist owing to the difficulties of monitoring survival at the nest. We examined survival of nestling prairie voles Microtus ochrogaster in alfalfa and bluegrass habitats over a 25-y period using the proportion of young estimated to have been born to pregnant females and to have survived to first capture at ≤13 g. Nestling survival did not differ between habitats, but was greater during spring-early autumn than during late autumn–winter and greater during late autumn than winter. Survival of nestlings was also greater during the increase phase than during the decline or trough phases irrespective of season. During most increase phases greater nestling survival may have resulted from hibernation of snakes. Predation from snakes did not appear to be involved in decreased survival during the decline phase, at least for declines occurring during late autumn-winter. We suggest extreme weather and maternal death from predation as potential causes of decreased survival of nestlings in winter declines.