Age at maturity is a particularly important life history parameter, as it predicts potential life time reproductive success in many small mammal species. Animals should therefore optimize the timing of maturation by reacting to environmental stimuli that predict future environmental conditions. Photoperiod often reliably predicts ecological conditions. Animals born into a photoperiod indicating favorable conditions (spring, summer) may mature earlier and at a lower weight than animals born into conditions indicating unfavorable conditions (autumn, winter). So far most work was done on small, altricial rodent species and we still lack knowledge about their precocial relatives. Precocial animals are born much further developed than altricials and might show less plasticity in their ontogenetic trajectory than the latter. We tested the influence of photoperiod simulated by increasing (spring) or decreasing (autumn) light in climate chambers on important life history parameters in a medium sized rodent, the highly precocial cavy (Cavia aperea). We wanted to determine whether photoperiod influences timing of maturation and early growth in male cavies and whether patterns of testosterone in blood are reflected by patterns of testosterone metabolites in feces.Males born into simulated spring grew faster and matured at an earlier age than males born into simulated autumn conditions. Patterns of testosterone in blood correlated with testosterone metabolites measured in feces. Male cavies strongly react to predictive photoperiod cues by adjusting growth and timing of maturation as we found previously for females, corroborating the importance of seasonal cues for adjustments of life history.