Meeting Abstract
P3.73 Monday, Jan. 6 15:30 Is the Use of Torpor by Hummingbirds Limited in Landscapes with Warm Nighttime Temperatures? SCHROEDER, RJ*; POWERS, DR; WETHINGTON, SM; George Fox Univ., Newberg, OR; George Fox Univ., Newberg, OR; Hummingbird Monitoring Network, Patagonia, AZ rschroeder11@georgefox.edu
Hummingbirds are found across landscapes that differ markedly in temperature extremes. If the temperature profile of a landscape requires hummingbirds to function well outside thermoneutral conditions increased thermoregulatory costs might make balancing their daily energy budget difficult. Hummingbirds can use nocturnal torpor to compensate for daily energy shortfalls, but it is unclear if a hypothermic strategy would be useful if landscape temperature profiles include warm nights. To study the use of torpor by hummingbirds in landscapes characterized by warm nighttime temperatures we examined torpor use in broad-billed hummingbirds (Cynanthus latirostris) from two landscapes where nocturnal temperatures differed by ~10 °C (Harshaw Creek; HC, ~4-27 °C vs. Sonoita Creek; SC, ~14-32 °C) in SE Arizona. Torpor use was tracked using open-flow respirometry on hummingbirds exposed to natural temperature cycles. Torpor was used by all birds (n = 7) at HC, but only 63% of birds (n = 8) at SC. SC birds entered torpor later and spent less time in torpor (4.75 h) than HC birds (5.3 h). Generally cooler temperatures at HC may increase daily thermoregulatory costs necessitating torpor use. Further, the HC temperature profile would allow birds to select roosting sites with temperature minimums near minimum tolerated body temperature (~12 °C ). Reduced torpor use at SC could be due to lower daytime thermoregulatory costs making use of nocturnal torpor less necessary. Alternatively, higher nighttime temperatures at SC might reduce the energetic benefits of torpor. If the latter is true then predicted patterns of climate change that could raise both daytime and nighttime temperatures might limit the effectiveness of torpor use when energy shortfalls occur.
