Every morning, exactly at 4:40 the birds start tweeting outside! Not at 4:39 or 4:41, but 4:40 right on the dot. It's almost like an alarm goes off somewhere in nature and wakes all the birds up.
I noticed this last year as well, and may have even blogged about it. Now that I'm on the 2nd floor I'm much closer to the tree tops and hear them even better. Thank goodness they don't get the birds inside started, they wait for sunrise.
Something to look forward to. Chirping and tweeting birds.