Reindeer

Both males and females carry antlers, which no other deer does, and the female's are retained through winter — useful for clearing snow from lichen and for defending a feeding crater. The hooves change with the seasons, spreading soft and broad on summer ground and hardening to rimmed edges that cut ice and dig through crust in winter.

The threat now is precipitation as much as temperature. Warming brings rain onto snowpack, which refreezes into a sealed layer of ice the animals cannot break, and herds starve above food they can smell. Add industrial roads and pipelines fragmenting migration corridors and several subpopulations have fallen by more than half in two decades, which is what moved a species numbering in the millions onto the Vulnerable list.