Geese migrate to find colder weather for the summer.
It gets colder in winter and the geese want to have the same temperature all year so when it gets cold they move to where it is warmer.
It gets warmer in the summer and geese want it to be as cold as possible so when it gets warm they move to where it is colder.
It gets warmer in the winter and geese want it cold so they move to where it is colder.