That bird seed must be great stuff. When I lived in an apartment with a balcony, I had a couple of windowboxes with plants in them hooked onto the balcony railing. I wondered how all the odd little weeds that kept sprouting up in those boxes got there. There was a regular little forest of them growing there.
Then I realized that the woman upstairs, who had a similar balcony, liked to feed the birds, and she came out on her balcony and scattered birdseed with a liberal hand, and some of it must have landed in my windowboxes.