Meeting Abstract

P1.100  Friday, Jan. 4  Use of Torpor by a High- and Mid-Elevation Hummingbird Species in Southeastern Arizona ANDREW, J.L.*; POWERS, D.R.; WETHINGTON, S.M.; George Fox University, Newberg, OR; George Fox University, Newberg, OR; Hummingbird Monitoring Network, Patagonia, AZ jluke11@gmail.com

Studies have shown that hummingbirds enter nocturnal torpor when energy reserves fall below specific “threshold” levels. The existence of a threshold suggests that it is favorable to remain normothermic, possibly to avoid physiological consequence of prolonged hypothermia. We studied nocturnal torpor use in broad-billed hummingbirds (Cynanthus latirostris; mid elevation; n=8) and broad-tailed hummingbirds (Selasphorus platycerus; high elevation; n=7) that were free-living during the day to assess the adequacy of available energy resources to allow for maintenance of normothermic metabolism at night. Nocturnal metabolic rate was measured using standard open-flow respirometry, under BMR conditions, at temperatures ranging from 5-38 °C. We found that all individuals of both species entered torpor shortly after the beginning of their nocturnal fast, and did not emerge from torpor until ~1 hour before sunrise. The consistent use of torpor in two species living in distinct ecosystems suggests that these birds might regularly use nocturnal hypothermia to balance their energy budget. If true then these hummingbirds might not experience the physiological consequences of extended hypothermia seen in other animals. Supported by NASA, Richter Scholar Program (George Fox University).