Perpetual Motion Machines

There are two bridges I can pass under on my walk along the hike and bike trail.  Theses birds live under the second bridge and I have long been frustrated by the fact that they are never still or even slow enough for me to get much of a picture.  Today , I found out what the problem is---I believe they are Swifts, possibly Chimney Swifts.  They are fast, they never stop and they don't perch, because their feet are only suited for clinging.  Maybe some day I can get a better shot, but for now, this will have to do!