More than you want to know about A Swallow Song RICHARD & MIMI FARINA ~ A Swallow Song ~ http://youtu.be/zHNSAK-iWy0
Have not yet found written documentation, but the story as I remember it is that Richard wrote this song for his sister-in-law Joan Baez during or after a visit to San Juan Capistrano when the swallows returned (traditionally March 19th).
Mission San Juan Capistrano is named after Saint John of Capistrano -- San Giovanni da Capestrano. Again from Wikipedia: "John was known as the "Scourge of the Jews" for his fanatical anti-semitism. In 1447 he offered the Pope a small fleet on which to load all the Jews of the papal states in order to ship them to some faraway land. Between 1451 and 1453, his fiery sermons against Jews persuaded many southern German regions to expel their entire Jewish population, and at Breslau some were burned at the stake." http://en.wikipedia.org/wiki/John_of_Capistrano
"And will the swallows come again?" Wikipedia tells us that "In recent years, the swallows have failed to return in large flocks to the [San Juan Capistrano] Mission. Few birds were counted in the 1990s and 2000s. The reduction has been connected to increased development of the area, including many more choices of nesting place and fewer insects to eat."
". . . songstress Carolyn Hester learned the Sephardic song, Los Bilbilicos at a song-swapping group in Greenwich Village in the early 1960s. The melody is an extremely well known setting of the Sabbath table song, Tzur Mishelo. Hester recorded it on a 1962 LP that is best known these days for Bob Dylan's harmonica playing on several tracks. Hester's husband at the time, Richard Fariña, heard the song and adapted it into The Swallow Song ? which he recorded with his next wife, Mimi, on their second album, Reflections in a Crystal Wind." http://www.sephardicmusic.org/second_halfc_survey.htm#levy
Hester sings these lyrics, which are . . . found in a 1960 songbook by Theodore Bikel called "Folksongs and Footnotes":
LOS BIBILICOS Los bibilicos cantan / En los arbos de la flor Los bibilicos cantan / En los arbos de la flor Debaxo se asentan / Los que sufren del amor. Debaxo se asentan / Los que sufren del amor.
Bikel translates it: The nightbirds are singing In the flowering trees, While underneath sit those That suffer from love.
https://www.facebook.com/video/video.php?v=487031703749 Carolyn Hester says she learned Los Bibilicos at at song swap. The person she learned it from might have learned it from the Theodore Bikel songbook. Although the song does not appear on any of his commercial recordings, he was recorded singing it as part of a lecture 'History and Origin of Jewish Music" https://digital.library.upenn.edu/webbin/freedman/lookupalbum?hr&catlg=B-007%28l%29