I've been watching birds come and go at the feeder for a little over a month now. It's taken a while, but I'm starting to see some consistent patterns emerge. The finches usually come in first, typically around 30-45 minutes after first light, followed by the sparrows a little later, and finally the doves. The sparrows and the doves mostly feed under the feeders, picking up the seeds dropped by the finches, which probably explains their late arrival. Why show up early if the finches aren't there to drop enough seeds on the ground to make it worth your while?
The two things that often disrupt this predictable pattern are, a) my presence in the yard with a camera, and b) a visit by my buddy the Scrub Jay (above). Depending upon the particular level of spookiness in the finch flock for the day (and it's beyond me why they can be so tame one day, and so completely wild and spooky the next), either of us have the potential to chase off the flock, which stops the flow of seed, which causes the sparrows and doves to go looking elsewhere for food.
Assuming it's not too late in the day, this ephemeral food chain usually reconstructs itself fairly quickly after being disrupted. First, I'll see one or two finches land in the top of the tree above the feeders. Then, they'll hesitantly work their way down branch-by-branch, with the bravest finally feeling comfortable enough to take up position on the feeder and commence with spilling seed again. Once that line is crossed, other finches soon follow, and before you know it, the sparrows and the doves are back too, feeding under the finches as before. This continues on for a while, at least until one of us spooks the finches again, which starts the entire process over.