A lot of dinosaur fossils have been found on Alaska's North Slope. the reading passage think that why those dinosaurs can survive in winter is the migration hypothesis. the reading passage said that there is warmer than nowadays.

First, it's about the diet of those dinosaurs, the listening said that there are so much vegetation  grow there. they still have many food to support their life, so they don't have to migrate to other place.

second, live in herd  can give extra protection to those dinosaurs like other animals,  it can't support then to migrate. 

Finally, some of the dinosaurs can't migrate for a long distance,so they need to stay there and  find a way to surviver.