Believe it or not, we already have a technology for nighttime bird migration monitoring: weather radar.
This is made to compare two birds and their migration pattern over the last year.
Birds seem to have different radar signatures so that there is a different pattern for each bird.
Instead, it talks about data from partners, sources, etc., and even mentions some of them as manual counts, overlapping, etc.
It just looks radar-ish, but is not.