The article fails to mention the ravens cannot leave because their wings are clipped, leaving them unable to fly. So there would likely be no "relationship" if the ravens were not intentionally crippled.
https://en.wikipedia.org/wiki/Ravens_of_the_Tower_of_London#...
> Appointed in 2011, current Ravenmaster Christopher Skaife was caring for seven of the birds in 2018.[33] He has reduced the amount of clipping of wings and feathers by a third to allow the ravens to fly, instead of merely hopping or gliding. He has allowed one of the birds, Merlina, to fly to the wharf on the Thames but she always returns due to the bonding with her keeper.[34]
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."
If the birds are staying because they like it, or have some special "bond" then why clip them at all? Clearly they can't fully fly as they would naturally. It doesn't add up.
Most birds are social animals (including Ravens) and prefer to stay with their flock (which includes caretaker humans), so it's not really about making sure the birds are kept prisoner. Pet birds will occasionally fly away because they're spooked (e.g. from a bird of prey) or get lost. Once they've flown far enough away, you're likely not to see them again. [0][1]
There are those who free flight their birds, but that requires lots of training and requires constant monitoring of the birds, calling out to them when they get too far. Birds rely on loud calls to find their way back to their flock (hence why they squawk all the time--its a natural homing beacon meant for large distances).
I'd say semi-clipped wings are probably a good compromise without constant monitoring. These birds will outlive birds in the wild, while still having a greater degree of freedom.
Those are all excuses to justify keeping the ravens captive because of a ridiculous superstition. The only ethical thing is to not keep these birds and let ravens (and all birds for that matter) live their lives naturally in the wild.
I could chain you up "just a little" and let you have a walk now and then and even feed you well and treat you nicely, but you would still be a prisoner and it would be wrong for me to do that to you.
I'm not sure that crippled is necessarily the wrong word, but I wanted to clarify that wing clipping is not permanent. It is a shortening of feathers, that would be undone by the annual moult.
If they do it continually, so the birds can never fly off, what is the difference? It's needlessly cruel, all because of a superstition. Seems to me that birds are meant to fly.