Mixed-species flocks and feeding aggregations are groups of different birds that share a similar feeding style, and all decide to “roll out” as a crew (Or in the case of an aggregation, “hang out”). This is always handy because it means you see a variety of different birds all in the same area, just doing their thing and getting along.
One of the prevalent species in the flock I saw were Chestnut-Backed Chickadees, which are a lot like a Chickadee, only brown. They were usually providing the lookout and making sure the coast was clear before the other birds came in.
This project is going to get a lot more difficult when I run out of birds.
This was taken with my 70-200mm f4 lens, zoomed in to 200mm. I was shooting at 1/100 with an aperture of 6.3, and ISO 1000. Your basic overcast day.