The Return of the Devil Bird™

The Devil Bird™ has returned. Monica was able to make visual contact late this evening, and reported back that...

...'twas a large fellow, perched on one leg 'e was, with a mean and dirty look...

Oops. Wrong description, but close. What she actually said was something like...

I saw it in a tree! And it was big!

Each night the Devil Bird™ stretches his neck to the sky as his ghastly melody penetrates the walls, windows, and everything else within screeching distance, leaving unanswered the haunting question...

What is it?