If a wild black rat mated with a wild brown rat would the offspring be sterile?
I’m assuming you mean the different species Rattus rattus (black rat) and Rattus norveigus (brown rat). IF they could (or would) interbreed, the offspring would probably be infertile. However, these rats rarely coexist anywhere and have different habits. The black rat is arboreal. The brown rat lives close to the ground or under it. They are considerably different in size and shape and would not likely see the other species as something to breed with. In fact when the two species come in contact, the brown rat almost always kills the black rat.
