Flocking geese

For the last few evenings I have witnessed some interesting behaviour. Around about 7pm a group of may be twenty Canada geese fly over the garden towards the sun set. After 10 or 15 mins another larger group, or perhaps the same group with more individuals fly over in the the same direction and this carries on for half an hour or so with the group growing to perhaps 60 or 70. Then as it starts to get dark 8.20-8.30 some of this large group fly back sometimes in smaller groups 8-12 perhaps but also in one huge flock of several hundred. They must congregating somewhere not too far away and then going home to roost.