I live in a redwood forest and it is noticeably quieter of insect and bird sounds compared to nearby down out of the forest a bit, but not as silent as in an old growth grove.
The redwood canopy blocks out a lot of light, the thicker it is, the harder for any plants to grow down below. The redwood leaves acidify the soil over time as they fall, there is a limited range of plants that can handle it. And then the trees themselves are highly insect resistant, there are no insects living in bark for example.
So basically: bottom of the food chain for birds isn't there, especially not down on the floor in old growth with so much light blocked out.
The redwood canopy blocks out a lot of light, the thicker it is, the harder for any plants to grow down below. The redwood leaves acidify the soil over time as they fall, there is a limited range of plants that can handle it. And then the trees themselves are highly insect resistant, there are no insects living in bark for example.
So basically: bottom of the food chain for birds isn't there, especially not down on the floor in old growth with so much light blocked out.