I opened the balcony door a bit so the cat could go in and out. Suddenly the cat rushed back in, low to the floor and I heard magpies making a racket. I guess they had discovered the cat. I went and stood in the balcony doorway. There were four birds in the birch tree opposite my balcony: A chickadee, a starling and two magpies. Some more squawking from the magpies, and two more settled in the tree, along with another starling a couple more chickadees. As I watched, over a half-dozen chickadees arrived to settle in the top of the birch. One "dive-bombed" my balcony a couple of times.
I thought of the Hitchcock movie "The Birds" and then got curious about where "The Birds" author Daphne du Maurier got her idea from. Turns out, she got them from seagulls, and she describes a site I've seen a lot here in Norway.
That said, I wish I had a camera. I didn't mind seeing all the birds in one tree, though my cat was reluctant to go back out on the balcony.