The frozen tundra (Midwest America 1/5/14). Below zero temperatures are extremely rough on stray cats. You can help warm a half a dozen with one sunlamp, on your porch.
Aim it pointing down about two feet off the ground under a porch or awning. Create, or put in areas that block the wind. Place an old blanket or rug on concrete floors to hold the heat from the lamp.
When it is seven degrees outside, without wind, it is twenty five to forty degrees warmer under on of those red 250w sunlamp bulbs, when about two feet high. That is enough heat to greatly help theses poor furry rodent controllers.
These Columbus, Ohio homeowners, weighted down several boxes, and used an old car cover, on their covered porch, to block the wind. Make sure the lamp is very secure, and not close to anything flammable, as cold cats will clime around warm things. These people added a few plastic ties to reinforce the clamp, to make sure the lamp will stay in place.
A small metal pan of water can also remain unfrozen under these bulbs, but it takes up the space. Water freezes in minutes with these temperatures, so make sure they have water, not ice. And of course they need serious food to help keep them warm from the inside out.