1. Understanding the determinants of reproduction is a central question in evolutionary ecology. In pulsed resources environments, the reproduction and population dynamics of seed consumers is driven by pulsed production of seeds by trees, or mast-seeding. In Southern Québec, eastern chipmunks (Tamias striatus) exclusively reproduce during the summer before and the spring after a mast-seeding event of American beech. They thus seem to anticipate beech mast by reproducing during early summer, so that juveniles can emerge at the time of maximum beechnut abundance during late summer. 2. However, the cues allowing chipmunks to anticipate beech mast remain unknown, and the existence of the anticipation process itself has been questioned. To tackle those issues, we investigated the links between the nutritional ecology and reproduction of adult chipmunks and compared their spring diet in mast- vs post-mast years. 3. We monitored female’s reproductive status (N=446), analyzed cheek pouch contents at capture (n=3761 captures), and recorded seed production by deciduous trees on three different sites in Mont-Sutton from 2006 to 2018. 4. Results revealed a systematic shift in chipmunk diet towards red maple seeds in springs preceding a beech mast, with red maple seeds composing more than 77% of chipmunk diet. However, red maple consumption was unrelated to red maple production, but was related to beech seed production in the upcoming fall. We also found that red maple consumption best predicted the proportion of females in summer estrus. 5. Our results confirm that chipmunks anticipate beech mast-seeding and suggest a key role of red maple consumption in that anticipation. Results also suggest that red maple seeds may contain nutrients or secondary-plant components essential to sustain or trigger the summer reproduction in chipmunks, which allow them to remain synchronized with pulsed productions of both red maple and beech and improve their fitness. 08-Jan-2020