The thermal and energetic significance of cavity roosting in Mountain Chickadees and Juniper Titmice

I examined the thermal and energetic benefits of cavity roosting in summer and winter-acclimatized Mountain Chickadees (Poecile gambeli) and Juniper Titmice (Baeolophus griseus). Reduction of wind speed inside the cavity increased standard operative temperature 2.5 to 5.9 degrees C compared to the open sites in summer and 12.1 to 14.7 degrees C in winter. Nocturnal energy savings ranged from 23.8 to 27.9% for summer birds and 25.1 to 37.6% for winter birds roosting in cavities. Wind speed was significantly lower inside cavities compared to open sites. These energy savings result in increased fasting endurance of 2.2 to 3 hr in summer and 5.7 to 7.3 hr in winter, which may be critically important for survival throughout the annual cycle for these two species.