I recently happened to capture this nice threesome of pine siskins encircling our Nyjer (niger) seed feeder. As you can see, the birds were concentrated in the bottom few inches of the feeder because we had let the seed supply run low. When the feeder is full, they tend to arrange themselves more vertically.
In the photo immediately above, you can see (especially if you click on the photo to see it larger) a bit of the yellow feathers on the wings on the bird on the right. A better view of this distinctive splash of yellow can be seen in the photo below, taken in December 2010.
I have written about pine siskins in several earlier posts, collected here.