Collision avoidance radar?

There's a stand of birch trees about 15 feet from the end of the porch, two large ones and two small.
The big ones might be 70 feet tall, the others a little shorter. Among the branches the chickadees gather as they stage for their dive to the feeder full of black sunflower seeds.  Sometimes you can see them coming from a long distance, their wavelike flight pattern a straight line to the feeder or the staging tree.
     So many of them  gather at times I'm reminded  of sailors manning the rigging of a tall ship. It seems every branch and twig is alive with a bird.
     Given the size of the trees you can imagine the maze of branches and twigs reaching almost from the ground, up to 70 feet in the air.
     Watching the birds flit among the branches today raised a serious question. Chickadees only have one speed when they fly — fast. So, given fast, how can they tear around all those twigs at top speed and never hit even a little twig? I've seen them bump into each other around the feeder, but never in the trees. What allows them to zoom through all that brush? Do they have bat radar?
     There may be a reason they learn to fly headlong through a thicket of twigs and branches. A merlin came by today, a falcon-family bird of prey. He made a couple of dives at chickadees but they escaped into the mesh. Being considerably larger, the merlin couldn't follow into that tangle and he gave up fairly quickly.
     Whatever the reason, maybe those folks designing driverless cars and trucks could learn something from the chickadees. Elon Musk are you following?

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