When I annotated my own small collection of non-organism observations, eggshell and nest were common among them.
Personally I would favour “home” for nest as it is easily translatable and removes the need for dozens of home types in the list.
While we wait for “eggshell” to be covered, through the excellent process being conducted in this thread, does anyone have a suggested annotation? Mine are usually a single broken shell on the ground. Occasionally an unbroken one…presumably that is organism, life stage=egg? And, if cold, dead?