I've never thought about the first part. I just assumed it had been outside for a while since it was 12 weeks old.I think hardiness may be relative to the environment in which silkies are raised in. Meaning, if 8 week old babies have been outside and gradually gotten used to the diminishing temperatures, they may be fine without a heat lamp. But, if someone has been keeping 8 week olds inside and wants to move them out into a coop...they may need a heat source. I also believe that wind, wind chill factor and dampness all make a difference. I now use AccuWeather which calculates a RealFeel temp based on a variety of factors. The app works well in the summer also, when humidity plays a role.

The ones I'm talking about were raised by broody until week 4 and then I had a heat lamp until week 6. After that, they weren't even using it, and were snuggling with their older siblings.