1
general::
The individual sought has gone away, as in Jean hoped to meet her editor at long last, but when she arrived the bird had flown. This idiom has been used for an escaped prisoner, and more generally, as in 1655 by William Gurnall (The Christian in Complete Armour): "Man . . . knows not his time . . . he comes when the bird is flown." [Mid-1600s]
American Heritage Idioms