I understand that there was nothing waiting for them and crops take time to grow, but what prevented them from effictively supplimenting their food supplies by foraging and hunting until crops could be grown and a more stable food source established? And did they bring any kind of farm animals with them? Thanks!
You say "always", but are there some specific instances you are referring too?
In the case of the Pilgrims you could refer to William Bradford's diary. They did forage and hunt, but the Pilgrims' food hardships were exacerbated by their initial communal division of production. http://mith.umd.edu/eada/html/display.php?docs=bradford_history.xml