I saw the movie "Lili" with Leslie Caron, Mel Ferrer and Jean-Pierre Aumont along with Zsa Zsa Gabor many years ago. Leslie sings the song to a sock puppet and the words are as follows:

On every tree, there is a bird,
Singing a song of love,
On every tree, there is a bird,
And every one I ever heard,
Could break my heart without a word,
Singing a song of love.

REFRAIN: A song of love is a sad song,
Hi-Lilli Hi-Lilli Hi-Lo,
A song of love is a song of woe,
Don't ask me how I know,
A song of love is a sad song,
For I have loved and it's so,
I sit by my window and watch the rain,
Hi-Lilli Hi-Lilli Hi-Lo,
Tomorrow I'll probably love again,
Hi-Lilli Hi-Lilli Hi-Lo.

PS: I'm 77 yrs. old, Leslie Caron is 76. J.