Using a Thermal Camera to Measure Heat Loss Through Bird Feather Coats

Summary

This protocol describes the quantification of heat transmission through a flat skinned avian specimen using a thermal camera and hot water bath. The method allows obtaining of quantitative, comparative data about the thermal performance of feather coats across species using dried flat skin specimens.

Abstract

Feathers are essential to insulation, and therefore to the cost of thermoregulation, in birds. There is robust literature on the energetic cost of thermoregulation in birds across a variety of ecological circumstances. However, few studies characterize the contribution of the feathers alone to thermoregulation. Several previous studies have established methods for measuring the insulation value of animal pelts, but they require destructive sampling methods that are problematic for birds, whose feathers are not distributed evenly across the skin. More information is needed about 1) how the contribution of feathers to thermoregulation varies both across and within species and 2) how feather coats may change over space and time. Reported here is a method for rapidly and directly measuring the thermal performance of feather coats and the skin using dried whole skin specimens, without the need to destroy the skin specimen. This method isolates and measures the thermal gradient across a feather coat in a way that measurements of heat loss and metabolic cost in live birds, which use behavioral and physiological strategies to thermoregulate, cannot. The method employs a thermal camera, which allows the rapid collection of quantitative thermal data to measure heat loss from a stable source through the skin. This protocol can easily be applied to various research questions, is applicable to any avian taxa, and does not require destruction of the skin specimen. Finally, it will further the understanding of the importance of passive thermoregulation in birds by simplifying and accelerating the collection of quantitative data.

Introduction

Feathers are the defining characteristic of birds and serve many functions, among the most crucial being insulation¹. Birds have the highest average core temperatures of any vertebrate group, and feathers insulating them from environmental temperature changes are a vital part of energy balance, especially in cold environments². Despite the importance of feathers, the majority of literature on changes in thermal condition in birds has focused on metabolic responses to temperature variation rather than the function of feathers as insulation^3,4,

Protocol

This work did not involve any work with live animals and was therefore exempt from animal care review.

1. Set-up and materials (Figure 1)

1. If flat skins of the species of interest are not available, use Spaw’s protocol²⁹ to create skins from fresh or frozen specimens. Preen feathers into a neat, natural position, and dry to obtain a constant weight before proceeding with measurements.
2. Set up a constant temperature hot water bath.
   NOTE: This set-up is quite tall, so it is easiest to place the hot water bath on the floor.
3. Place a sheet of clear acrylic glass (Table of....

Results

Representative results from a series of one individual of each of five species, measured at six temperatures, are presented in Figure 4 and Figure 5. These show that small variations in the placement of the skin can result in variations in the readings of up to 1.7 °C. Figure 4 shows how training of an investigator increases repeatability of the measurements. For example, the same individual house sparrow (Passer domesticus.......

Discussion

This paper provides a protocol for repeatable, standardized thermal imaging measurements of avian flat skin specimens. This method makes it possible to compare thermal performance of the feather coat among species, within species, between comparable individuals, and at different locations on the bodies of individuals, all without destruction of the specimen.

The availability of necessary materials and equipment may be a limitation of this method. Although thermal cameras are rapidly becoming m.......

Materials

Name	Company	Catalog Number	Comments
Aluminum Foil	Reynolds Wrap	109000831	30 square ft.; this exact model need not be used.
Foam Core Board	Foamular	20WE	1 in. x 4 ft. x 8 ft; this exact model need no be used.
General Purpose Water Bath	PolyScience	WB02	Ambiet +5 °C to 100 °C; ±.01 °C
PDF Data logger	Elitech	RC-51H	Built in temperature and humidity sensor
Plexiglass	AdirOffice	1212-3-C	Acrylic glass; 12 in. x 12 in. x 1/8 in.; this exact model need not be used.
Thermal Image Analysis Software	FLIR	ResearchIR Max v4.40.7.26 (64-bit)	Allows collection of precise, quantitative thermal data
Thermal Imaging Camera	FLIR	SC655	680x480-pixel resolution, ±2 °C or ±2% accuracy, 40 cm minimum focusing distance
Tripod	The Audubon Shop	The Birder Tripod with Manfrotto 700RC2 Rapid Release Head	65" maximum height; this exact model need not be used.