One of the presentations given at the Northern England Raptor Forum meeting on Saturday was by Stephen Murphy from Natural England. He presented the data he has collected about the dispersal of Hen Harriers from the Forest of Bowland using GPS tracking devices. The ability to monitor the movements of these birds clearly helps gain a better understanding of their needs. One bird had travelled from Bowland to Portugal and had returned to his nest site. Comments were made about how the birds tend to move between favoured roosts, many of which are associated with grouse moors. This will come as no surprise to many.
The birds are not tracked continuously as I believe the GPS packs do not have enough battery power so there are some gaps in cover, but it is still possible to gain a good idea of the birds movements.
I have not been able to find any detail on the web for Natural England's tracking (perhaps I have not found the right place) but if you would like to see the potential of the technique have a look at the Cairngorms website where similar work is taking place.