A very nice capture on film - do you remember what your focal length was? Capturing birds in the film era before auto focus was challenging, or impossible in flight.
I find getting close to kestrels is not easy - they alway seem to have a flight radius of >50 yards for me - I did get lucky the last time I was at Bosque though - this little fellow would hover and hover and hover just over one of the viewing platforms on the east side of the northern drive around letting me capture lots of frames - a few I thought were worth keeping https://pathfinder.smugmug.com/Travel/Bosque-del-Apache-January-2016/i-3JVzBNX/A
