Just that many more of them are present in the atmosphere than reentering space debris pieces.

> many more of them are present in the atmosphere

At 36,000 feet?

Why not? What comes down must come from somewhere up.

Exactly! If you think about it, every meteorite has passed through 36,000 feet at some point!

What makes a meteorite not "space debris" though?

The same which makes fallen leaves in the forest not "garbage". Space debris is man-made, meteorites aren't and hence are not space debris [1].

[1] https://www.esa.int/Space_Safety/Clean_Space/What_is_space_d...

still a lot more birds than meteorites or spacecraft.

There are not many birds at cruising altitude. Some, but not many.

still more than spaceships and meteorites!

Estimates vary, but a ballpark figure is 25 million meteors hitting the Earth every day.

There is usually blood on the plane when it's birds.

We are nearly at the peak of the annual Orionid meteor shower. [0] There should be a higher probability of encountering meteor debris during this period than during periods where there are no meteor showers in progress. We are passing through the debris from Halley's Comet right now and for about another two weeks.

[0]https://www.space.com/stargazing/meteor-showers/orionid-mete...