It depends what the mother hens might be able to find for the chicks.  For example, hens used to pick through the poop of cattle/horses, to find the undigested seeds, but if they don't have access to that type of manure, it will make it difficult for them to find those same undigested seeds.  In summer they eat a lot of greenery and bugs, but what about in winter?  Depending on your climate, if the ground is frozen and/or covered in snow most of the time and they don't have access to a barn where they can forage from the dropped feed of other animals, they will starve if you don't feed them.  You can't find something that isn't there to find.