Fine-scale landscape phenology revealed through time-lapse imagery: implications for conservation and management of an endangered migratory herbivore

Climate change modifies plant phenology through shifts in seasonal temperature and precipitation. Because the timing of plant growth can limit herbivore population dynamics, climatic alteration of historical patterns of vegetation seasonality may alter population trajectories in such taxa. Thus, sound management decisions may depend on understanding how plant growth varies across a landscape within and among distinct management units or protected areas. Here, we examine spatial variation in the timing of spring plant growth, measured using a network of automated time-lapse cameras distributed across the range of endangered Sierra Nevada bighorn sheep (Ovis canadensis sierrae) in California, USA. We tracked greenness of individual plants across 2 years to compare spatial patterns of forage phenology in snowy and drought years. Green-up timing was derived for individual plants across the camera network and compared with local estimates of green-up timing from satellite data. Satellite-derived estimates of green-up timing showed strong correspondence with camera-derived estimates in areas with dense vegetation cover and weak correspondence in areas with sparse vegetation cover. Daily time-lapse imagery revealed consistent variation in green-up timing across elevation, both among latitudinal zones and among individual plant species. Green-up timing was earlier in 2020 than in 2019, reflecting differences in the end of the snowy season. Because bighorn forage seasonally on alpine species with a brief growing period, spring migration of bighorn may be linked to variation in snowmelt and plant growth across elevational gradients.