No, polar bears does not migrate.
It is the last one if more eggs are produced by chickens they will lose more weight
The Earth Is billions of years old and Earth is much more different now than it was then.
Hermit crabs live in large colonies so there is no real answer. You can put up to 10 hermits in a 10 gallon aquarium or 4 to 6 in the smallest plastic cage safely. They do eat but very little and can go several days up to two weeks without food. They store water in the back of their shell for moisture for their gills.