Rabbits were thought to have been introduced to the UK by William the Conqueror (therefore not technically a native species!) and for centuries were a delicacy only for the nobility and royalty. Eventually the rabbits escaped the warrens and dispersed into the landscape and bred, well, like rabbits. I'm guessing that as the meat was the preserve of nobility during Cadfael's time (1130s-50s-ish) the furs were too.
I guess this could be set any time during the TV series or after book #2: One Corpse Too Many. I don't know if there are any books it is set before, I'm only at book #3: Monk's Hood! This is pure, unabashed fluff.
"Cadfael," said Hugh from where he was propped up against the stone doorway. "I'm not sure the Abbot would approve if you started keeping rabbits in your herbarium. Not to mention you'd be stealing from the King."
"I'm not going to steal one, Hugh," said the monk in question, sitting atop a wooden crate in one of the castle's storerooms, a rabbit in his arms and its cage, lid open, at his feet. One of the other three rabbits remaining in the cage had its paws up on the edge of the open hole and was looking around the small storeroom, nose twitching. "I am just making sure that they are being well cared for whilst they are here."
Hugh thought he was here for more than just checking up on the cargo, making its way to one of the King's warrens further north, but he didn't say anything. His friend looked far too comfortable with his fingers stroking the soft grey fur, as did the rabbit, who had tucked its head into the warm folds of Cadfael's habit.
"I will make sure they are fed and watered and looked after, Cadfael. Nothing will harm them."
The curious rabbit jumped up atop its cage and Hugh hurriedly moved into the room and shut the door behind him to ensure the precious cargo didn't try to escape. The rabbit ignored him and leapt down to the floor and with a sudden burst of restless speed shot between two crates then around another cage before completing the circuit of the room by jumping over Cadfael's feet to land near Hugh.
Hugh bent down to grab the rabbit before it decided to do another mad dash around the room. It struggled in his arms for a moment, kicking him in the stomach, before calming down. He wasn't sure quite how to hold it but wrapping his arms around it like a baby seemed to be a safe way.
It was strangely nice holding the rabbit. He had only seen them in passing as they were transported through the town, a creature jealously guarded by the king and the nobles lucky enough to own a warren. It was different from holding rabbit fur too; that he was acquainted with, as deputy sheriff he had previously been charged with the care and keeping of several passing lord's possessions, including one or two rabbit fur cloaks. It was somehow comforting to hold a warm, living and breathing creature in his arms.
The rabbit shifted and kicked him in the stomach again. He quickly put it back in its cage and shut the lid to ensure it didn't escape, but not before giving it one last stroke: its fur was ever so soft. He looked up at Cadfael, the old monk smiling warmly down at him.
"God's creatures really are beautiful. I feel blessed to have gotten to meet these ones." Cadfael carefully put his rabbit back in its cage and secured the latch, then, after standing up and brushing the fur off his habit, laid on hand on his friend's arm. "Thank you, Hugh, for letting me see them. I know that only your chosen men and the soldiers that came with them were supposed to be near them."
"You're welcome," said Hugh with a smile, guiding the elderly monk out of the room with a gentle hand on his back. He took one last look at the small stack of cages and the movement he could see within them then locked the door behind them.
"Lord Beringar!" came a call from down the corridor.
"Well," said Cadfael, patting Hugh on the arm. "I'd better leave you to your duties." He looked out of the window at the pink streaking across the sky. "And if I linger any longer I'll be late for Vespers!"