Do Hummingbirds Actually Sleep?

Methods

Summary

Study Sites and Animals. I will conduct this study at the Southwestern Research Station (SWRS) in the Chiricahua Mountains (Cochise County; 31.883703, -109.206344, alt. 1650-1720m), SE Arizona.  SWRS was dominated by oak (Quercus sp.), Juniper (Juniperus sp.), and pinyon pine (Pinus sp.). This site was selected because it offerred a wide variety of hummingbird species whose populations are regularly banded, massed, and assessed for molt. We will study an opportunisitic forager, the black-chinned hummingbird (Archilocus alexandri; ~3.0 g), a trap-liner, the magnificent Hummingbird (Eugenes fulgens; ~7.5g), and the territorialist blue-throated hummingbird, (Lampornis clemenciae; ~8.0g). All three species are migratory and breed in SE Arizona.

Torpor Measurement. Hummingbirds used in this study will be trapped at dusk to allow them to accumulate energy as naturally as possible. The hummingbirds will then be housed in 1m³ cages and provided with food ad. Libitum to make sure they begin torpor measurements with a full crop (Calder et al. 1990). At the time hummingbirds would begin roosting they will be weighed to the nearest 0.1g and returned to their cage. Cages will be placed outdoors so that hummingbirds will experience natural light and temperature cycles.  Nighttime ambient temperature wll be measured using Cu-Cn thermocouples (type-T) read continuously using TC-2000 thermocouple reader (Sable Systems) and recorded using Warthog LabHelper software (http://warthog.ucr.edu). 

Surface temperature. Surface temperature will be measured to track changes in core body temperature throughout the night.  Measurements will focus on the eye heat dissipation area (Powers et al. 2015) as this is an area with low feather density allowing skin surface temperature to be directly measured. Hummingbird surface temperature will be measured at 15-minute intervals on caged birds using infrared thermography (FLIR SC6700; accuracy 0.1 °C). The high resolution of the SC6700 should allow me to detect even small changes in surface temperature.  Analysis of infrared thermography will be done using ResearhIR software (FLIR, Inc.) and ImageJ software (NIH). All analysis will be done using a Macintosh Macbook Pro laptop computer. 

Challenges

The biggest challenges for this experiment will be how the bird positions itself in the cage.  It is possible that the bird will roost somewhere other than the perches provided (e.g. the side of the cage.  If this occurs we will attempt to reposition the cage so we can still get video images.

Pre Analysis Plan

To analyze our data we will extract single-frame images from videos using ResearchIR software, from which we will measure surface temperature around the eye HDA using ImageJ software.  ImageJ will allow us to measure skin surface temperature changes from these images over the course of the night.