Annual brown fat dynamics in Pipistrellus hesperus and Myotis californicus with special reference to winter flight activity

An examination of the annual changes in brown fat deposits of Pipistrellus hesperus and Myotis californicus reveals: 1. 1. P. hesperus reaches peak brown fat levels in January and February, declining rapidly through March and April, then increases gradually through the remainder of the year. 2. 2. M. californicus , on the other hand, maintains peak levels of brown fat from December through February, decreasing gradually through August, then increasing rapidly in the fall. 3. 3.The major brown fat deposits for both species are interscapular, jugular, squamooccipitocervical and carotid bodies. 4. 4.The interscapular deposit (which accounts for 50–70% of all brown fat) appears to be a good index of brown fat dynamics. 5. 5.Brown fat appears to be important in maintaining body temperature during night at cold ambient temperatures.