Though they are by no means only capable of living in these parts, they find the terrain of dead forests and wooden huts to be perfect, and thus don't naturally migrate.
Radbits aren't hostile creatures and can indeed be "tamed" by ponies looking for a pet.
However, the nature of the radbit is two things: Mating and feeding. There is not a lot else radbits do, apart from these things.
Predators of the radbit
Radbits, being completely passive creatures with no effective means to defend themselves often find that they are prey to larger animals, such as radhogs, radigators, wolves, dogs and the occasional yao guai. Essentially any creature larger then the radbit which feeds off meat will eat a radbit given the chance.
Pony hunters have also confirmed the relative ease of killing radbits, though a steady aim and low calibre rifle must often be used due to damage that the larger calibres would do. (Essentially destroying the whole body in overkill.)
Radbit meat has proven to be a tasty, nutritious snack to hunters, but radbit meat alone is not enough to live off.
Diet of radbits
Radbits will eat anything given to them, short of rocks, gems and metal.
They have been known to devour entire trees amongst a group of them. It was once recorded that a mega-swarm of over 500 radbits once ate a dead forest the size of the everfree.
However, in capativity, they will eat pre-war food, cardboard, paper and books, some fabrics, wood, and gnaw on plastic (though their stomach is unable to digest it, they still have been known to chew through plastic containers to get to pre-war foods inside.
Surprisngly, not a great deal is known about the mating requirements of radbits other then if two radbits are left together, male and female, for any longer then three days, there will be a pregnancy within the female.
Pregnancy lasts for twelve weeks within the radbit society, before a baby is born. A baby radbit is then capable of reproducing after just two months, male or female.
this has led to some very dangerous situations involving literal tidalwaves of radbits in the past, occasionally reaching the scale of mega-swarm (over 250 radbits.) The largest mega-swarm ever recorded was 513 radbits (Coincidentally, this was the swarm mentioned previously) and their end only came once a fully trained hunting team of over 20 ponies was dispatched into the local area.
Though mega-swarms often starve themselves to death under their pure size, left unchecked with further food stocks they can become a threat to any community nearby.
In Side Stories
Radbits appear in Fallout: Equestria - Broken Bonds.