How Do Wild Animals Survive Extreme & Unusual Cold Weather?

Robins were at my neighbor’s house sitting around a pipe vent probably coming from a natural gas water heater, a flock of robins near the warm vent. I’ve also seen robins & cardinals sitting on the edge of a heated cattle tank, many dozens of them on a very frigid winter morning circling the top of the tank. I’m just wondering how the feral cat I feed has been surviving. Not even eating that much, comes around about 25% of what it did last winter and doesn’t finish the food either. I think someone else is sharing & they are keeping each other warm.