Thanks waterwingz for the info! Time to track down a SX50! :-D It seems Canon sold all the sx50 refurbs judging by the missing cadence over at slickdeals.net. I'm off to craigslist...or eBay where the sold, used listings on eBay seem to start around $110.
Based on the sx50 bird photos I've seen on the web I don't think I'll miss the quality of my d5500/tamron 150-600mm for the trade up to the CHDK sx50 for the increased zoom capability. Of course the nikon will still be used for in-flight photography/hand held efforts.
Maybe in the future there could be a motion tracking system that talks between the bescor motorized tripod and the CHDK that will find the bird, determine proper zoom and shutter speed based on available light and amount of motion, then optimally zoom to fill the frame. The technology is there, we just need a software/hardware geek with some time on their hands and a passion for it...