Effect of Solar Absorptance on Midday Radiant Heat Transfer in Terrestrial Mammals: Thermoregulatory Considerations for the Management of Captive Exotic Species

V.A. Langman and M. Rowe Center for Animal Welfare, USDA and University of West Indies

ABSTRACTMeasuring solar absorptance of live animal coats or skin quantifies the amount of solar heat that an animal will be exposed to during the day. The purpose of this study was to measure solar absorptance on a range of live animals to quantify the heat gain by solar radiation. A Swissteco® micro-solarimeter was used to measure solar radiation absorbed and reflected from an animal coat. Solar absorptance was measured on twenty-eight species in zoos and holding areas in the United States. In this study terrestrial mammals reflected an average of 24 % of incoming solar radiation and absorbed the rest 76 %. Pinnipeds reflect less solar heat on average 11% and absorb more 89%. In both groups there were significant variations. Przewalski’s wild horse (Equus caballus) reflect 48% of solar radiation. Sea lions (Zalophus californicnus) when first hauled out of the water reflect 8 % of solar radiation. The solar absorptance in the mammals measured averaged 76 % - 81 %. . Knowing the solar absorptance for an animal’s coat and the amount of solar radiation in the environment allows for the quantification of the solar heat load on the animal. An absorbed excess solar heat load will be compensated by behavioral thermoregulation such as shade seeking and nocturnal behavior or evaporative heat loss; panting or sweating.

INTRODUCTION• Gates (1980) made solar absorptance measurements on preserved

skins of mammals and birds in his laboratory. 100 measurements (all measurements in his lab) range of absorptances 0.445 – 0.946 and the range of reflectances 0.054 – 0.640. Dry birds or mammals did not have absorptances above 0.90 except Siamang (Hylobates syndactly) with a mean 0.946 absorptance. Finch (1972) measured reflectance of preserved skin samples from which absorptivity was calculated from eland (Taurotragus oryx) absorptance 0.71 – 0.79 with a mean reflectance 0.25 and Hartebeest (Alcelaphus lichtensteini) absorptance0.60 – 0.67 and a mean reflectance of 0.36. Hutchinson, Allen and Spence, 1975 made solar absorptance and reflectance measurements on three live species under ambient conditions. In this study, the results were Jersey heifers (Bos Taurus), and swamp water buffalos (Bubalusbubalis) both with a mean reflectance of 0.25 and sheep (Ovis arises) also with a mean reflectance of 0.25 the mean for all three species for absorptance was 0.75.

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REFERENCES

METHODS

RESULTS

CONCLUSIONS

The Swissteco® micro-solarimeter and a secondary standard were calibrated for each measurement using a board covered in BaSO4(Hutchinson, Allen and Spence, 1975). BaSO4 has average reflectance to shortwave radiation in the 400nm – 800 nm range of 0.977. The micro-solarimeter was held above the BaSO4 board to measure direct solar radiation and held 2 cm above the board to measure reflected solar radiation. The micro-solarimeter was held 2 cm above the secondary standard to measure reflected solar radiation (Fig,1). The solar absorptance measurements were made immediately after the calibration. The micro-solarimeter was held 2 cm above the animal’s coat and a reading taken (Fig. 2). The micro-solarimeter was then held 2 cm above the secondary standard on the animal to account for the curvature of the animal

The Swissteco® micro-solarimeter measuring the amount of solar radiation from the skin of an Indian elephant (Elephas maximus). The micro-solarimeter was held 2 cm above the coat and the secondary standard and readings taken.

Table 1. The reflectance and absorptance of 10 of the 42 species measured.RH – high sun reflectance; AH – High sun absorptance)

Species Part RH AH Bison bisonAmerican Bison Dorsal 0.25 0.75 Gates, 1980American Bison Dorsal 0.22 0.78 Equus caballusHorseWhite / light Grey

Dorsal 0.33 0.67 Red brown/chestnut

Dorsal 0.29 0.71 Grulla/black Dorsal 0.23 0.77 Equus caballusPrzewalski wild horse

Dorsal 0.48 0.52 Giraffa camelopardalisGiraffe Dorsal 0.28 0.72 Gates, 1980Giraffe Dorsal 0.28 0.72 Loxodonia AfricanaAfrican Elephant Ventral 0.23 0.77

Side 0.21 0.79 Inner Ear 0.22 0.78 Outside Ear 0.25 0.75

Elephas maximusIndian Elephant Dorsal 0.23 0.77

Ventral 0.23 0.77 Side 0.21 0.79 Inner Ear 0.20 0.80 Outside Ear 0.23 0.77 Madoqua kirki

Dik-Dik Dorsal 0.25 0.75 Dorsal 0.27 0.73 Dorsal 0.23 0.77

Ovibos moschatuMusk Ox Dorsal 0.17 0.83Rangifer tarandusReindeer Dorsal 0.25 0.75Camelus bactrianusBactrin Camels Dorsal 0.27 0.73

In this study solar absorptance measurements were made on the coats of live animals under natural solar radiation. The solar absorptance values ranged between 0.52 – 0.96. 1.Solar absorptance changes with different coat colors between species and within a species. 2. Wet coats have higher absorptance values than dry coats.3. Animals with coats that have high solar absorptance values require shade to avoid thermal stress from absorbed solar radiation.4. Knowing the solar absorptance for a species is a tool for animal husbandry and pen design.

Finch, V.A. 1972. Thermoregulation and heat balance of the East African eland and hartebeest. American Journal of Physiology. 222(6):1374-1378.

Gates, D.M. , 1980. Biophysical Ecology. Springer-Verlag: New York. p 611Hutchinson, J. C. D.,T. E. Allen and F.B. Spence 1975. Measurements of the

reflectances for solar radiiation of the coats of live animals. Comp. Biochem. Physiol. 52A: 343 - 349.

Langman, V.A., M. Rowe, D. Forthman, B. Whitton,N. Langman,T. Roberts,K.Huston,C. Boling, and D. Maloney. 1996. Thermal Assessment of Zoological Exhibits I: Sea Lion Enclosure at the Audubon Zoo. Zoo Biology 15:403-411.