Aviary birds- when is cold TOO cold?

[Ripeberry]

Hi, in my garden we have a large aviary attached to the shed and we keep 4 cockatiels in there.
Every morning i've been having to de-ice their water and it was -6c last night.
How cold does it have to get to be dangerous to cockatiels?
They have nesting boxes which i think they may use to huddle in but can't be sure.
AB

You may want to consider placing bubble wrap or something similar onto the outside of the avairy panels to help insulate it a bit.

My hubby used to fit thick plastic panels onto his avairy panels in winter and never had any problems.

Hope this helps.