Ask whether the bird is responding in flight to the local habitat vs. the topography?
A kingfisher flying up a stream, a Peregrine over an office building, harriers, kestrels, etc. hovering over a field are all interacting with the local environment therefore USING the area. Some of these are judgment calls admittedly, but migrants are virtually always well above (2 or 3 time) tree-top height or building height when in the act of flying over an area. Whether migrating or traveling a distance to forage at a specific site (e.g. gulls at a landfill), the birds collectively will also pass over in a very direct manner. Where small deviations from level flight is common in local birds (presumably for predator avoidance) such deviations are exceptional in migrants overhead, where such deviations cost too much of the energy stored up for the flight. Such birds traveling over an Atlas Block rarely respond to habitat-level features of the landscape but may use larger grain features such as lake shores or escarpments. A bird following a hedge row, tree line, stream corridor, or so
