Just like a large cup of coffee cools more slowly than a small one, a bear retains body heat more efficiently than a fox. A fox needs to produce more heat relative to its body size to keep warm. Beginning in late Summer, chickadees begin wedging seeds, insects and other food into tree bark and other crevices. They leave thousands of seeds cached throughout the half-mile range in which they spend their entire life. Later in the winter, perhaps when a bird feeder runs out of sunflower seeds, chickadees are somehow able to find the seeds they cached months earlier.
Chickadees have a fantastic memory.
Studies of chickadee brains reveal that the volume of the hippocampus, an area of the brain linked with memory, varies with the season. In fall, when a chickadee is hiding food, the hippocampus expands. In the spring, when there's no more need to find cached food, it contracts. In addition to brains that bulge with the season, chickadees physically adjust to a cold climate in many ways. In fall, they begin shivering.