Meeting Abstract
In summer, Chiricahua Mts (CM; SE Arizona) temperatures can be >40˚C. The CM supports migrating hummingbirds whose numbers and behavior differ on the west slope (WS) vs. east slope (ES) possibly due to the impact of thermal landscapes on energy expenditure. We studied variation in thermal landscapes between the WS and ES of the CM, and how differences might alter hummingbird energy budgets. To characterize thermal landscapes we recorded ambient (Ta) and operative (Te) temperature along transects sampling all vegetation types in our WS (~1700m-2000m) and ES (~1500m-1750m) sites. Mean daytime Ta did not differ between sites (WS 28.6±1.8 ˚C; ES 28.6±2.3˚C). Mean nighttime Ta was slightly higher on the ES (17.8±2.4˚C) than the WS (17.2±1.7˚C). WS hourly daytime Ta was higher in morning (0.4-2.1ºC) and afternoon (0.7-1.6ºC), but lower at midday (0.2-2.3ºC) relative to the ES. Maximum Ta (Tmax) occurred at 1400 on the WS and 1200 on the ES. Minimum nighttime Ta for both sites was at 0400. Prior to Tmax, Ta increased 2.3˚C/hr on the WS compared to 3.3˚C/hr on the ES. Following Tmax, WS Ta declined 2.0 ˚C/hr compared to 1.7 ˚C/hr on the ES. On the WS mean Ta is never above the predicted lower critical temperature (LCT) of small (~3g) hummingbirds, whereas larger (~7.5g) species are predicted to spend ~8 hours within their thermal neutral zone (TNZ). On the ES, small species are predicted to spend 4 hours within their TNZ compared to ~7 hours for large species. These data suggest that the differences in thermal landscapes are likely to have a greater impact on energy budgets of small hummingbirds than larger hummingbirds.
