During stormy weather the gray screech owl is ensconced in his New Year's Day nest box but leaves to hunt a few minutes earlier each evening. He may be hungrier in the cold -- I certainly am -- and because the sky is cloudy, stimulated to forage in the early darkness. Screech owl activity is triggered by amount of light as well as food demand. Nesting males leave their day roosts to hunt earlier when eggs hatch; and, as owlets grow, the males depart earlier and earlier, sometimes hunting in daytime if the sky is cloudy. They are solely responsible for feeding mates, who alone feed small nestlings.

Being hungrier, I eat more and am about three percent heavier in winter than in summer. I've learned that screech owls are heavier too -- an annual average seven to thirteen percent -- the amount positively related to food availability. The owls and other birds tell me that their heavyweights survive more often than lightweights during times of food scarcity in harsh winters -- that extra fat is adaptive. I suspect that winter-heavy humans inherited the same survival advantage from prehistoric ancestors, who experienced weather more directly and had to work a whole lot harder for their food than I do.