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

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.

scholarly journals Thermoregulation in desert birds: scaling and phylogenetic variation in heat tolerance and evaporative cooling

2021 ◽  
Vol 224 (Suppl 1) ◽  
pp. jeb229211
Author(s):  
Andrew E. McKechnie ◽  
Alexander R. Gerson ◽  
Blair O. Wolf
Keyword(s):  
Heat Tolerance ◽  
Heat Dissipation ◽  
Arid Zone ◽  
Resting Metabolic Rate ◽  
Heat Exposure ◽  
Published Data ◽  
Evaporative Heat Loss ◽  
Evaporative Water ◽  
Data Set ◽  
The Difference

ABSTRACTEvaporative heat dissipation is a key aspect of avian thermoregulation in hot environments. We quantified variation in avian thermoregulatory performance at high air temperatures (Ta) using published data on body temperature (Tb), evaporative water loss (EWL) and resting metabolic rate (RMR) measured under standardized conditions of very low humidity in 56 arid-zone species. Maximum Tb during acute heat exposure varied from 42.5±1.3°C in caprimulgids to 44.5±0.5°C in passerines. Among passerines, both maximum Tb and the difference between maximum and normothermic Tb decreased significantly with body mass (Mb). Scaling exponents for minimum thermoneutral EWL and maximum EWL were 0.825 and 0.801, respectively, even though evaporative scope (ratio of maximum to minimum EWL) varied widely among species. Upper critical limits of thermoneutrality (Tuc) varied by >20°C and maximum RMR during acute heat exposure scaled to Mb0.75 in both the overall data set and among passerines. The slope of RMR at Ta>Tuc increased significantly with Mb but was substantially higher among passerines, which rely on panting, compared with columbids, in which cutaneous evaporation predominates. Our analysis supports recent arguments that interspecific within-taxon variation in heat tolerance is functionally linked to evaporative scope and maximum ratios of evaporative heat loss (EHL) to metabolic heat production (MHP). We provide predictive equations for most variables related to avian heat tolerance. Metabolic costs of heat dissipation pathways, rather than capacity to increase EWL above baseline levels, appear to represent the major constraint on the upper limits of avian heat tolerance.

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

2017 ◽  
Author(s):  
Ben Smit ◽  
Maxine C. Whitfield ◽  
William A. Talbot ◽  
Alexander R. Gerson ◽  
Andrew E. McKechnie ◽  
...  
Keyword(s):  
Heat Tolerance ◽  
Heat Dissipation ◽  
Resting Metabolic Rate ◽  
Evaporative Cooling ◽  
Cooling Capacity ◽  
Evaporative Heat Loss ◽  
Cooling Efficiency ◽  
Evaporative Water ◽  
Cutaneous Evaporation ◽  
Hot Environments

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.

scholarly journals Seasonal physiological responses to heat in an alpine range-restricted bird: the Cape Rockjumper

2018 ◽  
Author(s):  
Krista N Oswald ◽  
Alan TK Lee ◽  
Ben Smit
Keyword(s):  
Physiological Stress ◽  
Resting Metabolic Rate ◽  
Evaporative Cooling ◽  
Cooling Capacity ◽  
Cooling Efficiency ◽  
Evaporative Water ◽  
Air Temperatures ◽  
Functional Value ◽  
Summer Temperatures ◽  
Physiological Adjustments

AbstractHot, dry summer conditions impose physiological stress on endotherms, yet we have a poor understanding of how endotherms seasonally adjust their costs of thermoregulation under hot conditions. We determined whether seasonal phenotypic plasticity in evaporative cooling capacity at high temperatures explained how the range-restricted Cape Rockjumper (Chaetops frenatus; hereafter “Rockjumper”), copes with hot and dry summer temperatures of the temperate mountain peaks of southwest South Africa. We measured evaporative water loss (EWL), resting metabolic rate (RMR), and body temperature (Tb) at high air temperatures (30 to 42°C) of individuals from a wild population of Rockjumpers during winter and summer (n = 11 winter, 4 females, 7 males; n = 10 summer, 6 females, 4 males). We found Rockjumper evaporative cooling in summer imposes higher EWL (i.e. greater water costs) compared to winter, although an accompanying lack of change in RMR resulted in increased summer cooling efficiency. These patterns are similar to those observed in species that inhabit regions where summer temperatures are routinely hot but not water stressed. Our findings show that avian seasonal physiological adjustments to heat can be diverse. Further seasonal studies on thermoregulation in the heat will greatly improve our knowledge of the functional value traits such as evaporative cooling efficiency and heat tolerance hold and how they contribute to the physiological stress organisms experience in heterogenous environments.

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

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.

scholarly journals Avian thermoregulation in the heat: is evaporative cooling more economical in nocturnal birds?

2018 ◽  
Author(s):  
Ryan S. O’Connor ◽  
Ben Smit ◽  
William A. Talbot ◽  
Alexander R. Gerson ◽  
R. Mark Brigham ◽  
...  
Keyword(s):  
Heat Dissipation ◽  
Heat Waves ◽  
Evaporative Cooling ◽  
Evaporative Heat Loss ◽  
Arid Environments ◽  
Evaporative Water ◽  
Air Temperatures ◽  
Nocturnal Species ◽  
Diurnal Species ◽  
Intense Heat

AbstractEvaporative cooling is a prerequisite for avian occupancy of hot, arid environments, and is the only avenue of heat dissipation when air temperatures (Ta) exceed body temperature (Tb). Whereas diurnal birds can potentially rehydrate throughout the day, nocturnal species typically forgo drinking between sunrise and sunset. We hypothesized that nocturnal birds have evolved reduced rates of evaporative water loss (EWL) and more economical evaporative cooling mechanisms than those of diurnal species that permit them to tolerate extended periods of intense heat without becoming lethally dehydrated. We used phylogenetically-informed regressions to compare EWL and evaporative cooling efficiency (ratio of evaporative heat loss [EHL] and metabolic heat production [MHP]; EHL/MHP) among nocturnal and diurnal birds at high Ta. We analyzed variation in three response variables: 1) slope of EWL at Tabetween 40 and 46°C, 2) EWL at Ta= 46°C, and 3) EHL/MHP at Ta= 46°C. Nocturnality emerged as a weak, negative predictor, with nocturnal species having slightly shallower slopes and reduced EWL compared to diurnal species of similar mass. In contrast, nocturnal activity was positively correlated with EHL/MHP, indicating a greater capacity for evaporative cooling in nocturnal birds. However, our analysis also revealed conspicuous differences among nocturnal taxa. Caprimulgids and Australian-owlet nightjars had shallower slopes and reduced EWL compared to similarly-sized diurnal species, whereas owls had EWL rates comparable to diurnal species. Consequently, our results did not unequivocally demonstrate more economical cooling among nocturnal birds. Owls predominately select refugia with cooler microclimates, but the more frequent and intense heat waves forecast for the 21stcentury may increase microclimate temperatures and the necessity for active heat dissipation, potentially increasing owls’ vulnerability to dehydration and hyperthermia.

scholarly journals Limited heat tolerance in a cold-adapted seabird: implications of a warming Arctic

2021 ◽  
Vol 224 (13) ◽  
Author(s):  
Emily S. Choy ◽  
Ryan S. O'Connor ◽  
H. Grant Gilchrist ◽  
Anna L. Hargreaves ◽  
Oliver P. Love ◽  
...  
Keyword(s):  
Metabolic Rate ◽  
Heat Tolerance ◽  
Water Loss ◽  
Resting Metabolic Rate ◽  
Evaporative Cooling ◽  
Evaporative Water Loss ◽  
Cooling Efficiency ◽  
Direct Effects ◽  
Evaporative Water ◽  
Rate Of Increase

ABSTRACT The Arctic is warming at approximately twice the global rate, with well-documented indirect effects on wildlife. However, few studies have examined the direct effects of warming temperatures on Arctic wildlife, leaving the importance of heat stress unclear. Here, we assessed the direct effects of increasing air temperatures on the physiology of thick-billed murres (Uria lomvia), an Arctic seabird with reported mortalities due to heat stress while nesting on sun-exposed cliffs. We used flow-through respirometry to measure the response of body temperature, resting metabolic rate, evaporative water loss and evaporative cooling efficiency (the ratio of evaporative heat loss to metabolic heat production) in murres while experimentally increasing air temperature. Murres had limited heat tolerance, exhibiting: (1) a low maximum body temperature (43.3°C); (2) a moderate increase in resting metabolic rate relative that within their thermoneutral zone (1.57 times); (3) a small increase in evaporative water loss rate relative that within their thermoneutral zone (1.26 times); and (4) a low maximum evaporative cooling efficiency (0.33). Moreover, evaporative cooling efficiency decreased with increasing air temperature, suggesting murres were producing heat at a faster rate than they were dissipating it. Larger murres also had a higher rate of increase in resting metabolic rate and a lower rate of increase in evaporative water loss than smaller murres; therefore, evaporative cooling efficiency declined with increasing body mass. As a cold-adapted bird, murres' limited heat tolerance likely explains their mortality on warm days. Direct effects of overheating on Arctic wildlife may be an important but under-reported impact of climate change.

scholarly journals Vocal panting: a novel thermoregulatory mechanism for enhancing heat tolerance in a desert-adapted bird

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Anaïs Pessato ◽  
Andrew E. McKechnie ◽  
Katherine L. Buchanan ◽  
Mylene M. Mariette
Keyword(s):  
Climate Change ◽  
Respiratory Tract ◽  
Heat Tolerance ◽  
Resting Metabolic Rate ◽  
Climate Change Impacts ◽  
Acoustic Signals ◽  
Evaporative Water ◽  
Air Temperatures ◽  
Specific Stage ◽  
Individual Repeatability

Abstract Animals thriving in hot deserts rely on extraordinary adaptations and thermoregulatory capacities to cope with heat. Uncovering such adaptations, and how they may be favoured by selection, is essential for predicting climate change impacts. Recently, the arid-adapted zebra finch was discovered to program their offspring’s development for heat, by producing ‘heat-calls’ during incubation in hot conditions. Intriguingly, heat-calls always occur during panting; and, strikingly, avian evaporative cooling mechanisms typically involve vibrating an element of the respiratory tract, which could conceivably produce sound. Therefore, we tested whether heat-call emission results from a particular thermoregulatory mechanism increasing the parent’s heat tolerance. We repeatedly measured resting metabolic rate, evaporative water loss (EWL) and heat tolerance in adult wild-derived captive zebra finches (n = 44) at increasing air temperatures up to 44 °C. We found high within-individual repeatability in thermoregulatory patterns, with heat-calling triggered at an individual-specific stage of panting. As expected for thermoregulatory mechanisms, both silent panting and heat-calling significantly increased EWL. However, only heat-calling resulted in greater heat tolerance, demonstrating that “vocal panting” brings a thermoregulatory benefit to the emitter. Our findings therefore not only improve our understanding of the evolution of passerine thermal adaptations, but also highlight a novel evolutionary precursor for acoustic signals.

scholarly journals Regularly drinking desert birds have greater evaporative cooling capacity and higher heat tolerance limits than non‐drinking species

2020 ◽  
Vol 34 (8) ◽  
pp. 1589-1600 ◽  
Author(s):  
Zenon J. Czenze ◽  
Ryno Kemp ◽  
Barry Jaarsveld ◽  
Marc T. Freeman ◽  
Ben Smit ◽  
...  
Keyword(s):  
Heat Tolerance ◽  
Evaporative Cooling ◽  
Cooling Capacity ◽  
Tolerance Limits

scholarly journals Physiological regulation of evaporative water loss in endotherms: is the little red kaluta ( Dasykaluta rosamondae ) an exception or the rule?

2014 ◽  
Vol 281 (1784) ◽  
pp. 20140149 ◽  
Author(s):  
Philip C. Withers ◽  
Christine E. Cooper
Keyword(s):  
Water Loss ◽  
Thermal Conductance ◽  
Vapour Pressure Deficit ◽  
Evaporative Water Loss ◽  
Water Vapour Pressure ◽  
Published Data ◽  
Evaporative Heat Loss ◽  
Evaporative Water ◽  
Physiological Regulation ◽  
Ambient Relative Humidity

It is a central paradigm of comparative physiology that the effect of humidity on evaporative water loss (EWL) is determined for most mammals and birds, in and below thermoneutrality, essentially by physics and is not under physiological regulation. Fick's law predicts that EWL should be inversely proportional to ambient relative humidity (RH) and linearly proportional to the water vapour pressure deficit (Δwvp) between animal and air. However, we show here for a small dasyurid marsupial, the little kaluta ( Dasykaluta rosamondae ), that EWL is essentially independent of RH (and Δwvp) at low RH (as are metabolic rate and thermal conductance). These results suggest regulation of a constant EWL independent of RH, a hitherto unappreciated capacity of endothermic vertebrates. Independence of EWL from RH conserves water and heat at low RH, and avoids physiological adjustments to changes in evaporative heat loss such as thermoregulation. Re-evaluation of previously published data for mammals and birds suggests that a lesser dependence of EWL on RH is observed more commonly than previously thought, suggesting that physiological independence of EWL of RH is not just an unusual capacity of a few species, such as the little kaluta, but a more general capability of many mammals and birds.

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