Timing of rainfall influences juvenile and yearling mass of a long-lived herbivore in a semiarid environment.

Resource availability is a primary factor predicting population performance. Synchrony between resource availability and consumer requirements plays a critical role in reproduction, and mismatches in the timing of resource availability and consumer requirements can have negative implications for reproductive success. Our objective was to determine when mass of juvenile and yearling white-tailed deer (Odocoileus virginianus) in semiarid rangelands is most negatively affected by limited forage availability. Thus, we determined the biological period when rainfall, a primary driver of resource availability, was most predictive of juvenile and yearling mass. Over 12 years, we captured 1,123 juveniles and yearlings across five distinct populations. We linked georeferenced capture records to rainfall data from biological seasons hypothesized to affect juvenile and yearling mass. We found that rainfall during the early growing season exhibited the strongest effect on mass. The resource pulse associated with early growing season rainfall is likely used to fuel fetal development during the critical final trimester of gestation. As environmental change continues to exacerbate the potential for mismatches in resource availability and consumer requirements to occur, it is important to identify when limited forage availability may most negatively affect reproduction to inform species conservation and support long-term sustainability.