Why Do Birds Go South in Winter?
We know why birds go south in the winter. The necessity of finding food to live upon has everything to do with that. As food grows scarce towards the end of summer in the farthest northern places where birds live, the birds there must find food elsewhere. They naturally turn south and when they find food, they have to divide with the birds living there. The result is that soon the food becomes scarce again and both the new-comers and the old residents, so to speak, are forced to seek places where food is plentiful. So both of these flocks, to use a short term, fly away to the south until they find food again and encounter a third flock or group of the bird family crowding the locality and exhausting the food supply. So in turn each flock presses for food upon the one in the locality next further to the south until we have a general movement to the south of practically all the birds until they reach a point where the food supply is sufficient for all for the time being.