Wildlife ecologists have seen white-tailed deer expanding their range in North America over many decades. And since the early-2000s these deer have moved north into the boreal forests of western Canada. These forests are full of spruce and pine trees, sandy soil and freezing winters with lots of snow. They can be a harsh winter wonderland. And ecologists haven't known whether a warmer climate in these forests or human land development might be driving the deer north. A recent study tries to disentangle these factors – and finds that a warming climate seems to play the most significant role in the movement of deer.