en_tn_lite_do_not_use/zec/10/08.md

I will whistle

To whistle is to produce a high, shrill sound with air through narrowed lips. It is often done to give a signal to other people, as here.

until there is no more room for them

The people will continue to go back to Judah and it will become crowded with no room for any more people to live there.