Thanks David for forwarding that message.
I have seen this fall gathering of Black Swifts a few times in my 35 years of record keeping here. Most of the time, I was camped in the South San Juan mountains and would see large numbers overhead. But I have only seen these large gatherings once or twice in the flat of the San Luis Valley. I believe the aphids on the trees those in flight had a lot to do with yesterday's incredible observation. I am headed there today to see if they are still around.
John Rawinski
Monte Vista, CO