Pomes in a Pail: Music

• MP3 short clip, hi-fi play (broadband)
• MP3 short clip, lo-fi play (modem)

There’s something called Biology
That, from an Acorn, makes a Tree
It knows the secret recipe
To Pea and Flea and Chimpanzee

It takes two parents — He plus She —
And somehow almost magic’ly
1 plus 1 adds up to 3
But here’s one thing that puzzles me:
What is the sum of Bird plus Bee?