Yes, you are correct. When birds sleep, their toes 'lock' in place around the perch and this is an entirely mechanical effect of the repositioning of the tendons from the 'crouching' as you say. They also know that the flamingos legs have some sort of similar mechanism (because of the fact that they were able to reproduce it with a dead bird) but I gathered from the article that they think it's made by the hip and/or the knee...
And yes, although nobody has been able to prove it, it's widely accepted that albatrosses sleep on the wing (swifts do it, too). But that's not what I find the most interesting about them! What amazes me about them is that they can fly over 6,000 miles without flapping once! These bird can fly across an ocean without actually flying and just using what's called dynamic gliding (or some such, I am not sure that is the precise term for it) but, basically, what it means is that their bodies are so aerodynamic and their wingspan is so long that they are able to 'ride' air currents and glide all the way without flapping once. What they do is move the angle of their wings so they can 'climb' the air currents (even against the wind!) by not only using the wings as the flaps on a plane wings but also very slightly banking in one direction and, when they reach a certain height (there is also a name for this 'zone' but I forget it now) and then go down slightly banking on the other direction just to do it over and over and over again so they can keep on advancing to the point that their hearbeat is the same during 'flight' that it is during rest. Now isn't that incredible?!
And you want another incredible fact about them? Their breeding season lasts one entire year from laying the egg to the baby (they have only one at a time) fledging! Good thing we don't keep them as pets, right?