Reaction norms for heat tolerance and evaporative cooling capacity do not vary across a climatic gradient in a passerine bird

AbstractLittle is known about the phylogenetic variation of avian evaporative cooling efficiency and heat tolerance in hot environments. We quantified thermoregulatory responses to high air temperature (Ta) in ~100-g representatives of three orders: African cuckoo (Cuculus gularis, Cuculiformes), lilac-breasted roller (Coracias caudatus, Coraciiformes), and Burchell’s starling (Lamprotornis australis, Passeriformes). All three species initiated respiratory mechanisms to increase evaporative heat dissipation when body temperature (Tb) approached 41.5°C in response to increasing Ta, with gular flutter observed in cuckoos and panting in rollers and starlings. Resting metabolic rate (RMR) and evaporative water loss (EWL) increased by quantitatively similar magnitudes in all three species, although maximum rates of EWL were proportionately lower in starlings. Evaporative cooling efficiency [defined as the ratio of evaporative heat loss (EHL) to metabolic heat production (MHP)] generally remained below 2.0 in cuckoos and starlings, but reached a maximum of ~3.5 in rollers. The high value for rollers reveals a very efficient evaporative cooling mechanism, and is similar to EHL/MHP maxima for similarly sized columbids which very effectively dissipate heat via cutaneous evaporation. This unexpected phylogenetic variation among the orders tested in the physiological mechanisms of heat dissipation is an important step toward determining the evolution of heat tolerance traits in desert birds.Summary statementWe show that avian evaporative cooling efficiency and heat tolerance display substantial taxonomic variation that are, unexpectedly, not systematically related to the use of panting versus gular flutter processes.

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Avian thermoregulation in the heat: phylogenetic variation among avian orders in evaporative cooling capacity and heat tolerance

Journal of Experimental Biology ◽

10.1242/jeb.174870 ◽

2018 ◽

Vol 221 (6) ◽

pp. jeb174870 ◽

Cited By ~ 22

Author(s):

Ben Smit ◽

Maxine C. Whitfield ◽

William A. Talbot ◽

Alexander R. Gerson ◽

Andrew E. McKechnie ◽

...

Keyword(s):

Heat Tolerance ◽

Evaporative Cooling ◽

Cooling Capacity

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Avian thermoregulation in the heat: scaling of heat tolerance and evaporative cooling capacity in three southern African arid-zone passerines

Journal of Experimental Biology ◽

10.1242/jeb.121749 ◽

2015 ◽

Vol 218 (11) ◽

pp. 1705-1714 ◽

Cited By ~ 78

Author(s):

M. C. Whitfield ◽

B. Smit ◽

A. E. McKechnie ◽

B. O. Wolf

Keyword(s):

Heat Tolerance ◽

Arid Zone ◽

Evaporative Cooling ◽

Cooling Capacity

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Efficient Evaporative Cooling and Pronounced Heat Tolerance in an Eagle-Owl, a Thick-Knee and a Sandgrouse

Frontiers in Ecology and Evolution ◽

10.3389/fevo.2021.799302 ◽

2021 ◽

Vol 9 ◽

Author(s):

Zenon J. Czenze ◽

Marc T. Freeman ◽

Ryno Kemp ◽

Barry van Jaarsveld ◽

Blair O. Wolf ◽

...

Keyword(s):

Heat Tolerance ◽

Resting Metabolic Rate ◽

Evaporative Cooling ◽

Heat Exposure ◽

Cooling Capacity ◽

Published Data ◽

Evaporative Heat Loss ◽

Evaporative Water ◽

Air Temperatures ◽

Eagle Owl

Avian evaporative cooling and the maintenance of body temperature (Tb) below lethal limits during heat exposure has received more attention in small species compared to larger-bodied taxa. Here, we examined thermoregulation at air temperatures (Tair) approaching and exceeding normothermic Tb in three larger birds that use gular flutter, thought to provide the basis for pronounced evaporative cooling capacity and heat tolerance. We quantified Tb, evaporative water loss (EWL) and resting metabolic rate (RMR) in the ∼170-g Namaqua sandgrouse (Pterocles namaqua), ∼430-g spotted thick-knee (Burhinus capensis) and ∼670-g spotted eagle-owl (Bubo africanus), using flow-through respirometry and a stepped Tair profile with very low chamber humidities. All three species tolerated Tair of 56–60°C before the onset of severe hyperthermia, with maximum Tb of 43.2°C, 44.3°C, and 44.2°C in sandgrouse, thick-knees and eagle-owls, respectively. Evaporative scope (i.e., maximum EWL/minimum thermoneutral EWL) was 7.4 in sandgrouse, 12.9 in thick-knees and 7.8 in eagle-owls. The relationship between RMR and Tair varied substantially among species: whereas thick-knees and eagle-owls showed clear upper critical limits of thermoneutrality above which RMR increased rapidly and linearly, sandgrouse did not. Maximum evaporative heat loss/metabolic heat production ranged from 2.8 (eagle-owls) to 5.5 (sandgrouse), the latter the highest avian value yet reported. Our data reveal some larger species with gular flutter possess pronounced evaporative cooling capacity and heat tolerance and, when taken together with published data, show thermoregulatory performance varies widely among species larger than 250 g. Our data for Namaqua sandgrouse reveal unexpectedly pronounced variation in the metabolic costs of evaporative cooling within the genus Pterocles.

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Interspecific variation in heat tolerance and evaporative cooling capacity among sympatric temperate-latitude bats

Canadian Journal of Zoology ◽

10.1139/cjz-2020-0276 ◽

2021 ◽

Author(s):

Matthew J. Noakes ◽

Andrew E. McKechnie ◽

R.M. Brigham

Keyword(s):

Heat Tolerance ◽

Core Body Temperature ◽

Resting Metabolic Rate ◽

Evaporative Cooling ◽

Interspecific Variation ◽

Cooling Capacity ◽

Myotis Lucifugus ◽

Temperate Latitude ◽

Evaporative Water ◽

Hoary Bats

We tested the hypothesis that interspecific variation in chiropteran heat tolerance and evaporative cooling capacity is correlated with day-roost microclimates, using three vespertilionid bats that occur sympatrically during summer in Saskatchewan, Canada. We predicted that hoary bats (Lasiurus cinereus Palisot de Beauvois, 1796; ~ 22 g) would have higher heat tolerance than little brown (Myotis lucifugus Le Conte, 1831; ~ 7 g) and silver-haired bats (Lasionycteris noctivagans Le Conte, 1831; ~ 13 g), as the latter two species roost in tree crevices/cavities that are more thermally buffered than the foliage roosts of hoary bats. We measured core body temperature (Tb; passive integrated transponder tags), evaporative water loss and resting metabolic rate (flow-through respirometry), while exposing individuals to a stepped profile of increasing air temperature (Ta) from ~ 30 °C in ~ 2 °C increments. Experiments were terminated when individuals became hyperthermic (Tb ≈ 42.5 °C), with maximum Ta (Ta,max) ranging from 42.0 °C – 49.7 °C. As predicted, hoary bats had the highest heat tolerance and evaporative cooling capacity, reaching Ta,max ~ 2.4 °C and 1.2 °C higher than little brown and silver-haired bats, respectively. Our results are consistent with the hypothesis that heat tolerance of bats is correlated with roost microclimates, although interspecific variation in body mass and phylogeny may confound these conclusions.

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Evaporative Cooling Options for Building Air-Conditioning: A Comprehensive Study for Climatic Conditions of Multan (Pakistan)

Energies ◽

10.3390/en13123061 ◽

2020 ◽

Vol 13 (12) ◽

pp. 3061 ◽

Cited By ~ 3

Author(s):

Shazia Noor ◽

Hadeed Ashraf ◽

Muhammad Sultan ◽

Zahid Mahmood Khan

Keyword(s):

Thermal Comfort ◽

Co2 Emissions ◽

Air Conditioning ◽

Evaporative Cooling ◽

Cooling Capacity ◽

Climatic Conditions ◽

Maximum Temperature ◽

Human Thermal Comfort ◽

Work Input ◽

System Configurations

This study provides comprehensive details of evaporative cooling options for building air-conditioning (AC) in Multan (Pakistan). Standalone evaporative cooling and standalone vapor compression AC (VCAC) systems are commonly used in Pakistan. Therefore, seven AC system configurations comprising of direct evaporative cooling (DEC), indirect evaporative cooling (IEC), VCAC, and their possible combinations, are explored for the climatic conditions of Multan. The study aims to explore the optimum AC system configuration for the building AC from the viewpoints of cooling capacity, system performance, energy consumption, and CO2 emissions. A simulation model was designed in DesignBuilder and simulated using EnergyPlus in order to optimize the applicability of the proposed systems. The standalone VCAC and hybrid IEC-VCAC & IEC-DEC-VCAC system configurations could achieve the desired human thermal comfort. The standalone DEC resulted in a maximum COP of 4.5, whereas, it was 2.1 in case of the hybrid IEC-DEC-VCAC system. The hybrid IEC-DEC-VCAC system achieved maximum temperature gradient (21 °C) and relatively less CO2 emissions as compared to standalone VCAC. In addition, it provided maximum cooling capacity (184 kW for work input of 100 kW), which is 85% higher than the standalone DEC system. Furthermore, it achieved neutral to slightly cool human thermal comfort i.e., 0 to −1 predicted mean vote and 30% of predicted percentage dissatisfied. Thus, the study concludes the hybrid IEC-DEC-VCAC as an optimum configuration for building AC in Multan.

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