Why do birds sing at night?

When I was a child, my maid (or mom if she came home early enough) would bring me to Taman Jaya to play in the evenings. I remember identifying the birds' twilight song as the alarm bell that signaled closing time. People would drift away and there would be only me left, still begging for five minutes more on the swing.

When I asked my maid what the birds were saying, she said that they were scolding me for not going home yet. The park belongs to them and their little birdies at night so I must hurry up and go home for my dinner!

I had this flashback yesterday. I was leaving Amcorp Mall at dusk when I heard the birds noisily singing in their trees. So nice that some things don't change. Thank God that the park still has birds!

And I still wonder why they sing at twilight...