Data from: Hovering in the heat: effects of environmental temperature on heat regulation in foraging hummingbirds

At high temperature (>40 ºC) endotherms experience reduced passive
heat dissipation (radiation, conduction, and convection) and increased
reliance on evaporative heat loss. High temperatures challenge flying
birds due to heat produced by wing muscles. Hummingbirds depend on flight
for foraging, yet inhabit hot regions. We used infrared thermography to
explore how lower passive heat dissipation during flight impacts body-heat
management in broad-billed (Cynanthus latirostris, 3.0g), black-chinned
(Archilochus alexandri, 3.0g), Rivoli’s (Eugenes fulgens, 7.5g), and
blue-throated (Lampornis clemenciae, 8.0g) hummingbirds in southeastern
Arizona and calliope hummingbirds (Selasphorus calliope, 2.6 g) in
Montana. Thermal gradients driving passive heat dissipation through eye,
shoulder and feet dissipation areas are eliminated between 36-40 ºC.
Thermal gradients persisted at higher temperatures in smaller species,
possibly allowing them to inhabit warmer sites. All species experienced
extended daytime periods lacking thermal gradients. Broad-billed
hummingbirds lacking thermal gradients regulated mean total-body surface
temperature at ~38 ºC suggesting behavioral thermoregulation.
Blue-throated hummingbirds were inactive when lacking passive heat
dissipation, so might have the lowest temperature tolerance of the four
species. Use of thermal refugia permitted hummingbirds to tolerate higher
temperatures, but climate change could eliminate refugia, forcing
distributional shifts in hummingbird populations.