Socioecological conditions are expected to influence the timing, or phenology, of when adult females give birth to offspring. Females may time reproduction such that offspring are born to maximize the length of the period that offspring have to forage during the growing season. In communal breeders, females may alter reproductive phenology to maximize benefits of group-living through synchronizing reproduction and improve offspring survival. We used an 11-year dataset on a population of communally breeding degus (Octodon degus) to test whether the (i) reproductive phenology was influenced by the abundance of food, social conditions, and the degree of masculinization of females and (ii) reproductive synchrony was influenced by similar access to food and degree of masculinization among females and communal litter size, in multi-female groups. The phenology of litter parturition (parturition day) was negatively associated with the abundance of food at burrow systems during winter (but not during spring) and was negatively associated with the number of adult females per social unit in the spring. Synchrony of litter production within communal groups increased in years with less available food. Our study suggests that degu females timed reproduction based the socioecological conditions likely to be experienced by their dependent offspring.