Condition-Dependent Nocturnal Hypothermia in Garden Warblers Sylvia borin at a Spring Stopover Site

[摘要] Migratorybirdshaveevolvedphysiologicalandbehaviouraladaptationsforcrossinglargeecologicalbarriersthroughtheaccumulationoflargeamountsoffatandproteinduringthepre-migratoryphase.Nevertheless,mostmigrantpasserinesusuallyneedseveralstopoversenroutetoreplenishtheirenergyreservesandtorest.Migratorydecisionsatastopoversitestronglydependonbodyconditionatarrival.Previousstudiesshowedthatleanbirdsprolongtheirstopovercomparedwithfatbirdsthatleaveafteraveryshorttime.Duringthestopover,leanbirdsmayreducetheirmetaboliccostsbyloweringbodytemperature(adaptivehypothermiahypothesis).However,itisnotclearwhetherhypothermiacanbeanactiveeconomisingstrategyorjustanunavoidableconsequenceofbadconditiontoavoidstarvation.Weusedtemperatureloggerstomeasureskintemperatureof19GardenWarblersSylviaborincaughtataspringstopoversite(PonzaIsland,TyrrhenianSea)andkeptovernightincottonbags.Wefoundthatbothbodyconditionandactivitywerepositivelycorrelatedwithskintemperatureduringthenight.Thedatashowedagradualnocturnaltemperaturedropofmorethan3°Cinleanbirds,particularlyinthecentralpartofthenight,followedbyarecoverytonormothermiclevels.Overall,birdsinworsephysicalconditionlostmorebodymassduringthenightthanbirdsinbettercondition,butthiswasespeciallytrueforbirdsthatloweredtheirbodytemperaturetheleast.Theseresultsindicatethathypothermiaisassociatedwithlowbodyconditionandthatitmaybefunctionalbyreducingbodymasslossduringmigration.

[学科分类] 动物科学

[关键词] Stopover