Juvenile survival is the most critical component of large herbivores’ population dynamics. Thus, large herbivorous mammals are expected to maximize their population growth rates by optimizing their recruitment rate through juvenile survival. Survival of calves is maximized when calving date and synchrony are well-adapted to the species’ environment. For instance, a short growing season for vegetation will promote a highly synchronized birth season to ensure that calves are born in most favorable conditions to grow and survive. To maintain this highly synchronous birth season, conceptions must also occur synchronously in time during the rutting season. Unfortunately, in a context of climate change, a ‘trophic mismatch’ may occur because climatic changes are faster than phenology changes of species, creating a situation where the peak demand for resources may now falls later or earlier than the seasonal peak of resource availability. Rangifer species is that thrive in a harsh and highly seasonal environment. However, reindeer have not received enough attention in regard to the global change debate. The aim of this project is thus to investigate if and how the reindeers’ reproductive phenology is evolving in the context of climatic change, e.g. by changing birthdates or onset of the rut period to adequately fit resources availability. I will first investigate effects of density and weather on the onset and synchrony of the rutting period. Then, I will focus on changes of the date and synchrony of the calving season in relation to both local and global climatic variables.