What is the suspected functional reason for the excavated nest tunnel being inclined upward?

Answer

To facilitate the flow of waste material out and minimize water seepage into the egg chamber.

The upward inclination of the horizontal tunnel is thought to be a design feature that facilitates the flow of waste material out of the chamber and minimizes potential water seepage into the eggs.

What is the suspected functional reason for the excavated nest tunnel being inclined upward?
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