"Koobly Double-take"

I've always had an interest in observing animal behavior.  These days, I primarily observe the nonsensical behavior of Fluffin.  What makes her so alert about the chirp of a distant bird?  When she hears a bird chirp she runs over to a window to try to look at the bird, as if she can jump out of the shut window to chase the bird.  She's notorious for doing this "double-take" when she actually sees a bird in the backyard.  She seems so alert when she does this.  I find animal behavior so interesting because animal behavior rarely ever has any rationale.  Maybe just Fluffin's behavior rarely ever has any rationale.