winter has cold temperatures & temperature is a property of the environment ->  an environment is cold in the winter  an environment is cold in the winter & cold environments usually have little food for animals ->  an environment usually has little food for animals in the winter  an environment usually has little food for animals in the winter & animals require food to survive ->  animals must move to an environment with more food in the winter  animals must move to an environment with more food in the winter & a warm environment usually has more food than a cold environment -> animals must move to a warmer environment during the winter to find food