11a_3n7a8044_paul bigelow Published January 25, 2019 at 3943 × 2629 in January 22-28, 2019 (Week 4 of 52): Most of Our Summer Birds Survive Winter Through Mass Migration ← Previous Next → Black-capped chickadees can lower their body temperatures at night by 20° F in a controlled state of torpor (photo by Paul Bigelow)