What is the stuff on their feet/legs? What is it for?
They are leather and brass anklets, during the manning (taming) of wild hawks they are used in conjunction with leather jesses (straps) to tether (tie down) the bird to a perch.
Once manned the anklets are left on but the jesses are removed during the hunt, while transporting the hawk in the field the anklets secure the jesses to the Falconers glove to prevent premature release and for safety reasons.
I hunt deciduous needleleaf forests mostly and it is very easy to lose sight of your hunting hawk even 25 feet in front of you so I attach a high quality hand made bell to the anklet and the tail, this keeps us together in the think woods.