I have a tubular birdfeeder with a fair amount of thistle seed in it. For the last couple of weeks I've had goldfinches by the dozens going after the food and occasionally a chickadee would grab a seed and run. Then I discovered a chickadee using a birdhouse near by. As the time went by, I saw more traffic to and from the birdhouse. I also noted that the goldfinches were dwindling in number. I attributed it to their come-and-go habits, but today I think I found out why the goldfinches were leaving. I saw a chickadee attack any bird that approached the feeder, and quite savagely, too. It was enough to change my notion of the chickadee as a nice, friendly creature with a nice, friendly bunch of calls. Every time a finch would approach, he or she would be chased away, in short order. And goldfinches are not noted for being non-aggressive to other birds, especially when there are thistle seeds to be had. I suspect the chickadees are protecting their home and food supply.