Which factor would have the greatest influence on the southern migration of animals living in the northern hemisphere

Animal migration is the relatively long-distance movement of individual animals, usually on a seasonal basis. It is the most common form of migration in ecology. It is found in all major animal groups, including birds, mammals, fish, reptiles, Many of these migrations are north-south, with species feeding and breeding in.

they float because they are less dense than the water itself

something denser than water, like a rock, will sink to the bottom

there's the proffessional site that will you.