Pursuit and escape drive fine-scale movement variation during migration in a temperate alpine ungulate

Climate change reduces snowpack, advances snowmelt phenology, drives summer warming,alters growing season precipitation regimes, and consequently modifies vegetation phenologyin mountain systems. Altitudinal migrants cope with seasonal variation in such conditions bymoving between seasonal ranges at different elevations, but vertical movements may becomplex and are often not unidirectional during the spring migratory season. We uncoverdrivers of vertical movement variation in an endangered alpine specialist, Sierra Nevadabighorn sheep. We used integrated step-selection analysis to determine factors that promotevertical movements, and factors that drive selection of destinations after vertical movements.Our results reveal that high temperatures consistently drive uphill movements, and providesome evidence for the contribution of precipitation events to downhill movements.Furthermore, bighorn select destinations that have a high relative index of forage growth andmaximize delay since snowmelt. These results indicate that although Sierra bighorn seek outforaging opportunities related to landscape phenology, they compensate for short-termenvironmental stressors by undertaking brief vertical movements. Migrants may therefore beimpacted by future warming and increased storm frequency or intensity, both in terms of theirfine-scale vertical movements, and in terms of tradeoffs between forage access and predationrisk.