The technique was developed from the observations of pale wisps seen moving on radar during the Second World War.
These were termed as "angels", "ghosts", or "phantoms" in Britain and were later identified as being caused by migrating birds.
Over time, the technology has been vastly improved with Doppler weather radars that allow the detection of birds, bats, as well as insects with resolution and sensitivity that is sufficient to quantify the speed of flaps that can sometimes aid in the identification of species.
It was however only in the 1950s through the work of Ernst Sutter at Zurich airport that more elusive "angels" were confirmed to be caused by small passerines.
[2] Early radar ornithology mainly focused, due to limitations of the equipment, on the seasonality, timing, intensity, and direction of flocks of birds in migration.