Im not sure of exact temps, but folks keep pigeons up far north as canada...so they can take alot of low temps.. but sometimes in extreme cold it would be nice for them to have a few heat lamps... that is in extreme places.. one still can do that in any cold temp state but not nessesary..
Two years ago we had about two weeks of -20 F, and even though my loft isn't heated, everyone was fine. It's been known to hit -30 F or so, and they manage to survive. ( I'm up in the Great White North of Ontario.)
We'll usually get a real cold spell for awhile in the winter. Hanging around zero and below. Sometimes the wind chill will be 20 below.
I have reptile heaters (the type that screws in a light socket), but only use them if the wind chill is really bad.....there's no draft in the loft but it gets biting cold
If you supply clean fresh water (during daylight hours),not froze, and a small interior box, kinda like a large nesting box (some even use an old 12 pack beer cardboard box with the end cut off) with some hay, or tim grass, or some other non toxic insulateing material that is edible for the Pigeons, AND it supplies a wind break for the pair, they will most likely be ok.
You must use common sense, and check on your Pigeons regularly. Do not let them (the box) get covered with snow!
The cardboard box is disposable (just incase anyone of you were wondering), just throw it away, and replace with a new one. (that's easy for some of us)
Usually it's about every 2 to 3 weeks or so.
Always supply clean, fresh, COLD Water on a regular basis. Cold water doe's not freeze as fast as warm/hot water.
Your Pigeons need regular exersize, daily, no matter what the temp is.
The must go for their food at least.
Do not coddle too much, and when the weather is nice, they will want to exersize even when you don't even want to go outside!
-40 below, plus any windchill for 2 to 3 days, with proper care. That's COLD!
Pigeons are tough!
Wild Pigeons, up here like to live under the small bridges that the gravel roads go over small creeks/rivers.
I think that the wind chill off of the frozen water would be more that I could take for 10 mins or so.
Keep that in mind.
They do enjoy flying in the cold.