RFID tags have rather limited read ranges - inches to feet, sometimes a few 
 yards.  Some newer technologies/tags may be usable at a few hundred  yards.
 
No passive rfid is likely to be trackable for miles.  Active tags have  
longer ranges, but require power sources, far too big for bees to  carry.  We  
have small, active tags that can mark a beehive or a  larger animal like a 
bear, and that can be picked up/read from a mile or  two.
 
Theoretically, you could tag bees at point of origin, set up readers at the 
 supposed end of the migration route, scan for bees with tags - but that's 
likely  to be really iffy.  I have no idea how you'd be able to make any 
guesses as  to where bees are going to go - or where they are coming from.
 
Drone aggregation areas have been identified using radar - but that simply  
looks for groups of bees in areas where you suspect the drones might go - 
the  detection limits are usually a few miles.
 
We've used lasers to detect bees at distances of a mile, and if you've a  
clear line of sight, you should be able to see bees at much greater  
distances.  The laser we used to 'see' bees at a mile are actually designed  to look 
at atmospheric chemistry at 30 miles up.  We had to detune this  instrument 
to avoid frying bees on the wing at a distance of a   mile. 
 
Looking at atmospheric chemistry 30 miles up vertically has the  advantage 
of unimpeded line of sight.  You're unlikely in hilly or  forested areas to 
be able to follow bees for any distance even remotely close to  30 miles.  
If you've really deep financial pockets, you might  mount a laser unit under 
a helicopter and follow migrating bees.  My   first  introduction to LIDAR 
(lasers) was tracking  plumes from  coal-fired power plant smokestacks, using 
a LIDAR in the belly of a fixed wing  aircraft.  One of the first LIDARs 
that we used to track bees was  originally designed to spot schools of fish in 
lakes from an airplane.  The  LIDAR was mounted on the floor of the plane, 
with a hole in the fuselage so that  the laser could scan the water.
 
Jerry
 
 
 
 
 

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