There is no 2 km distance. Bc water fowl like ducks, herons and geese fly over our property now and then. Droppings can be dangerous. The bigger the area chickens walk around. The bigger the chance my chickens walk across the droppings and get contaminated.if there is a distance of 2 km from the sick birds you are safe.
And in spring there are always a few ducks who search for a spot to nest near the well /small stream behind our garden.
So it doesn’t feel safe at all at the moment to let them free range.
But I did extend the run with another 12m2. It’s not escape proof but they can scratch in grasses and herbs a bit that way for at least one hour each day.