I am not sure if the GBH and the big white herons are migratory or not, but this past week to 10 days I have had 6 to 8 gbh and I counted eleven of the big white ones at the pond every morning. I also have two of the black herons at the pond. Smaller but they still eat my fish. I have been making my rounds at the pond early every morning and that seems to get rid of the gbh but the big white ones are much harder to discourage. I am attempting to discourage them coming to the pond by driving around the pond in the side by side.