Smarter than I realized!

I already knew the chickadees were intelligent, but this ... !

Background data:

• I am not a morning person. I tend to sleep in, if at all possible. (I once had a T-shirt/nightdress with the legend, "I don't do mornings." I wore it until it disintegrated into witches' lace; it was "me".)
• The chickadee feeder hangs outside my bedroom window, about a foot away, and maybe four feet from the head of my bed.
  
• I sleep with the window open.
• The chickadees are "morning persons". They are at the feeder at first light.

Sometimes, the feeder is low on seed, and by the time the chickadees have had breakfast, it has dropped below the level where their tiny beaks can reach. But they have devised a strategy for getting it filled again; they drum on the feeder until I wake up. "Tap, tap, tap, tap, tap. Tap, tap, tap, tap." And again, "Tap, tap, tap, ..." For a tiny bird, and a plastic bottle, the noise produced is surprising; as loud as an upholstery hammer with old-fashioned tacks. After a while, the tapping enters my dreams and I struggle to the surface, realize that I am guilty, yet again, of grave derelection of my duty, and creak out to fill a replacement feeder and hang it for them.

(I've posted this photo before. But it shows the structure of the feeder.)

I thought this was incredibly smart of these chickadees. I haven't seen others do that, in other places. Somehow, they have caught on to the fact that I am in hearing distance and will eventually respond. And they've taught the next generation to do it, too.

But I also thought that inventing the trick was probably a matter of accident: they were probably (I imagined) knocking on the bottle to shake the seeds into a position where the birds could reach them, and waking me up was just a side effect.

I may have to revise that opinion.

This morning, the tapping woke me up again. But I stood looking out the window for a few minutes before I dragged myself into the kitchen. And watched a chickadee tapping. He doesn't drum on the plastic at all; he turns himself around, and pecks at the end of the stick that goes right through the bottle, turning the whole thing into an echo chamber.

I tried it out, later (after I'd hung a refill). Tapping the bottle itself produces a muffled, "soft" sound. Tapping the perch is better. But to get the true wake-up call, you have to bang at the flat end of the stick, the one facing you in the photo above.

I find it hard to imagine them coming up with that by accident. What do you think?
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