Meeting Abstract

S10.8  Friday, Jan. 7  Hypothermia in small migrating passerines. What can bats teach us about bird migration? WOJCIECHOWSKI, Michal S.*; JEFIMOW, Malgorzata; PINSHOW, Berry; Nicolaus Copernicus University, Torun, Poland; Nicolaus Copernicus University, Torun, Poland; Jacob Blaustein Institutes for Desert Research, Ben-Gurion University, Israel mwojc@umk.pl

Small insectivorous bats are known to use torpor to facilitate fat accumulation prior to hibernation. In 1999 Speakman and Rowland found that this behavior is endogenously controlled, and that brown long-eared bats actively search for cold ambient temperatures to lower their energy expenditure during this preparatory period. Therefore, since before migratory flight small migrating passerines should face similar energetic challenges as insectivorous bats before hibernation, we asked whether small migrating passerines at stopovers also lower metabolic rate and body temperature (T_b) to facilitate fuel accumulation prior to flight by becoming hypothermic. We addressed the question using blackcaps (Sylvia atricapilla), a common Eurasian sylvid warbler. Consistent with our prediction, we found that during simulated migratory stopover, blackcaps lower T_b to >5°C below normothermic resting levels, which leads to a ~30% reduction in energy expenditure. More important, the deeper the hypothermia, the faster blackcaps restore their body mass during stopover. We also found that a further ~30% reduction of energy expenditure by migrating blackcaps during rest is possible when they huddle in groups of three or more sleeping birds. We also found that nocturnal hypothermia in blackcaps is not restricted to migration only, but occurs also in summer, while on the breeding grounds. Food deprived blackcaps lower T_b below their resting levels and the hypothermia is deeper in birds fasted longer. Based on these observations, we suggest that heterothermy in small passerines may be a common strategy used both as an emergency in face of energy limitation as well as while preparing for energy demanding activities.