The Union Square Squawk

Here's an odd one.

I can't remember when I started noticing it, but for at least the last two or three years, it's been a mystery that's befuddled me. Every morning as I emerge out of the mouth of University Place on my way to work in midtown, I walk by The Spingler Building, otherwise known as 5-9 Union Square West near East 14th. Emanating from somewhere unseen behind the latticework of fire-escape outside its second floor comes a tireless cacophony of squawking. I've looked and I've looked, but I cannot for the life of me pinpoint the source of the din. While I suppose it could be a malfunctioning machine of some kind (although I can't imagine any air conditioner making this sort of racket), the sound conjures to mind a nest of birds. That said, I've never heard a pigeon make this sort of noise. To stand beneath it in the mornings is maddening (how the tenants of the building deal with it I'll never know). Oddly, when I walk past it again in the evenings, it is silent. I can only assume that the mysterious buzzards or invisible pterodactyls that reside there take wing and flap through the city in the late afternoons, scouring for food to bring back back for their young.

Has anyone else ever noticed this?