[jamesgagan]

Found the info in the article referenced in the footnote. They are clipped but they can fly as far as the roof of the tower. If they do fly away, they catch them and bring them back.

"Their wings are also less severely clipped than they were in the past, giving them a greater ability to fly. Now they can flap up to the roofs of the Tower buildings, and Merlina, the raven most bonded to Skaife, flies so well that she regularly spends time outside the Tower walls. “They need freedom, but they also need protection,” Skaife says of his ravens, as a soldier would speak of the British people. His new regime has been a great success, though changes to the wing-clipping routine have resulted in several chases to retrieve ravens gone awol. One bird was returned to him—alive—inside a gym bag."

https://www.theatlantic.com/magazine/archive/2018/10/ravens-...