If you have kept fancy rats, you have kept Rattus norvegicus, the Norway rat. Domesticated centuries ago, the Norway rat is a placid, social, relatively slow-moving animal that establishes stable hierarchies and adapts well to cage life. Most modern rat husbandry (equipment, technique, expectations) is built around its assumptions. Other common pet rodents (hamsters, gerbils, mice) are different species entirely, with their own characteristics.
A physically different animal
The black rat, Rattus rattus… is a different animal from all of them.
A roof rat can climb a vertical wall. It can jump several feet horizontally from a standstill. It runs at speeds that exceed what a human eye can track, and it can squeeze through any opening larger than its skull. Wild roof rats live arboreally: in trees, in roof spaces, in the upper levels of buildings. They are solitary by temperament rather than colonial. They do not form the stable social hierarchies that Norway rats do. And they respond to threats and stress with intense flight rather than the freeze-and-assess response of their cousin species.
Its long, semi-prehensile tail is part of that toolkit: it grips, it counterbalances along a branch, and in a fall the rat can whip it to flip right-side up and land on its feet. Paired with a light build and a very low terminal velocity, that righting reflex makes a roof rat remarkably hard to injure in a fall, far more so than a heavier, ground-dwelling Norway rat. Its feet are built for the same arboreal life: larger and more muscular for its size, and capped with thick, tough pads that grip rough bark and bare wire alike. One practical result is that, unlike fancy rats, roof rats are not prone to bumblefoot.
Tamer, but still a roof rat
Eight years of selection has changed all of that behaviorally. These rats remain calm under handling, accept human interaction willingly, and tolerate close living conditions with other rats. But none of that has changed them physically. The tameness is genetic, present from birth, inherited rather than trained. The physical capabilities are unchanged from the wild type.
An advanced pet, not a beginner’s
This is what makes them advanced pets rather than beginner ones. Standard Norway rat housing (solid metal cages with reasonable-sized doors) works for them. What does NOT work is the large-door style of cage popular among fancy rat keepers. A roof rat that does not yet trust you, or one looking for an opening, will be past your hands and across the room before you have registered that the door is moving. Trusted, well-handled adults settle into cage routines and are not real escape risks. New or young animals very much are. So the infrastructure question is less about cage construction than about door design, room sealing, and the human factor: knowing how to open a cage of agile climbers without losing one.
They are easy to keep alive. They might not be living in your cage if you are careless.
People who have tried to start their own colonies have hit this issue more than any other. The animals themselves have rarely been the problem. The expectation that they would behave like fancy rats has been.
By the criteria PetSmart and similar guides use to rank pets, Rattus rattus sits squarely in the moderate-to-advanced range. They are easy to keep alive. They might not be living in your cage if you are careless. That is the difference, and it is the whole difference.
If that sounds like a challenge you would take on rather than a warning, see what it takes, and the mission to find successor breeders.