Weightless chickadees flit in on minimal wings, grab a seed, then disappear to batter the seed against a branch. It's amazing they can do that. Evolving smallward, they retained large skills.
House finches land heavy and sit bulky in the food trough, cracking seeds and spitting hulls overboard until another, hungrier, comes to evict.
Chickadees are difficult to count, all looking alike, and constantly coming and going. Are there two? Or ten? Or twelve?
House finches are variably coloured and frequently are poxed, with swollen eyes or lost toes, thus are relatively easy to count, if you have a lot of time, and a lot of seeds.