What is the meaning of the cover illustration of the Nightingales and Bombers LP by Manfred Mann?

For me the concept is showing the three "bombs" which are the three circles receding back into black negative space coming closer and closer to the viewer (or from the sky to the ground). The fact that nightingales sing during the night could also symbolize the bombs as a "wake up call" with the black background as the nighttime, or even because they sing during the day as a call that shows an attack. The bombs are the nightingales.
1975 (when the album was released) was also when the Vietnam War ended for the Americans. But since this group was British it resembles their war as well.
As said by Mann: "The title of this album [and apparently the cover art too] was inspired by a recording made in Surrey, England during the Second World War, by an ornithologist intending to record Nightingales. The bombers flew over at the same time and were recorded by accident. The recording has been incorporated in 'As Above, So Below'".