Deerly departed: Using motor-vehicle accidents to determine factors influencing white-tailed deer rut timing in Ontario, Canada

In seasonal environments conception is timed such that offspring are born at the peak of resource abundance. Although largely determined by photoperiod, reproductive timing can also be modulated by fluctuating environmental conditions. Some studies show that reproduction is occurring earlier, coinciding with an earlier spring as the climate warms. A failure to synchronize parturition with the advancing spring flush of resources can lower reproductive fitness; on the other hand, a longer growing season could be beneficial to some species. We asked whether breeding phenology of white-tailed deer (Odocoileus virginianus) has changed with changing environmental conditions. Using 29 years of wildlife motor-vehicle accident data (1988–2016) as an index of deer rut behaviour in southern Ontario, Canada, we assessed four deer management areas (DMAs) to determine: 1) whether timing of the white-tailed deer rut has changed; 2) whether the growing season has changed; and 3) whether changes in growing season and rut are correlated. We found that in the southwestern-most DMA the peak of the rut is 9 days earlier than in the northeastern-most DMA. The peak of the rut did not change over three decades. We detected an increase in the number of growing degree days, signifying both an earlier start to spring green-up and a later end to fall. The trend toward a longer growing season could have positive impacts on deer populations throughout the province.