I’m glad you brought up day/night length and temps as a combo. I have found that while a day of 25-30* and/or a night or 2 into the teens , which is fairly typical for us for a couple days in Jan, might not require blanketing, if we get a week of that and there’s little to no sun, I will see them looking or acting (lots more silly running around) more uncomfortable. They aren’t shivering (that I have seen, clearly I’m not out checking at 2am :lol:) but their display of comfort tells me more than enough. So, for extended periods of colder but not COLD weather, I may well end up putting blankets on.
Also, time of year matters too. 50* in Jan with a full Winter coat still, having acclimated to colder temps, will feel a lot warmer than 50* in August when there’s very little Winter coat and bodies have been acclimated to 80-90* weather.