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Czenze ZJ, Freeman MT, Kemp R, van Jaarsveld B, Wolf BO, McKechnie AE. Efficient Evaporative Cooling and Pronounced Heat Tolerance in an Eagle-Owl, a Thick-Knee and a Sandgrouse. Front Ecol Evol 2021. [DOI: 10.3389/fevo.2021.799302] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
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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2
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Heat tolerance in desert rodents is correlated with microclimate at inter- and intraspecific levels. J Comp Physiol B 2021; 191:575-588. [PMID: 33638667 DOI: 10.1007/s00360-021-01352-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2020] [Revised: 12/14/2020] [Accepted: 01/23/2021] [Indexed: 01/21/2023]
Abstract
Physiological diversity in thermoregulatory traits has been extensively investigated in both endo- and ectothermic vertebrates, with many studies revealing that thermal physiology has evolved in response to selection arising from climate. The majority of studies have investigated how adaptative variation in thermal physiology is correlated with broad-scale climate, but the role of fine-scale microclimate remains less clear . We hypothesised that the heat tolerance limits and evaporative cooling capacity of desert rodents are correlated with microclimates within species-specific diurnal refugia. We tested predictions arising from this hypothesis by comparing thermoregulation in the heat among arboreal black-tailed tree rats (Thallomys nigricauda), Namaqua rock rats (Micaelamys namaquensis) and hairy-footed gerbils (Gerbillurus paeba). Species and populations that occupy hotter diurnal microsites tolerated air temperatures (Ta) ~ 2-4 ℃ higher compared to those species occupying cooler, more thermally buffered microsites. Inter- and intraspecific variation in heat tolerance was attributable to ~ 30% greater evaporative water loss and ~ 44 % lower resting metabolic rates at high Ta, respectively. Our results suggest that microclimates within rodent diurnal refugia are an important correlate of intra- and interspecific physiological variation and reiterate the need to incorporate fine-scale microclimatic conditions when investigating adaptative variation in thermal physiology.
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3
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McKechnie AE, Gerson AR, Wolf BO. Thermoregulation in desert birds: scaling and phylogenetic variation in heat tolerance and evaporative cooling. J Exp Biol 2021; 224:224/Suppl_1/jeb229211. [PMID: 33627461 DOI: 10.1242/jeb.229211] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Evaporative heat dissipation is a key aspect of avian thermoregulation in hot environments. We quantified variation in avian thermoregulatory performance at high air temperatures (T a) using published data on body temperature (T b), evaporative water loss (EWL) and resting metabolic rate (RMR) measured under standardized conditions of very low humidity in 56 arid-zone species. Maximum T b 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 T b and the difference between maximum and normothermic T b decreased significantly with body mass (M b). 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 (T uc) varied by >20°C and maximum RMR during acute heat exposure scaled to M b 0.75 in both the overall data set and among passerines. The slope of RMR at T a>T uc increased significantly with M b 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.
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Affiliation(s)
- Andrew E McKechnie
- South African Research Chair in Conservation Physiology, South African National Biodiversity Institute, P.O. Box 754, Pretoria 0001, South Africa .,DSI-NRF Centre of Excellence at the FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Hatfield, Private Bag X20, Pretoria 0028, South Africa
| | - Alexander R Gerson
- Department of Biology, University of Massachusetts, Amherst, MA 01003-9297, USA
| | - Blair O Wolf
- UNM Biology Department, University of New Mexico, MSC03-2020, Albuquerque, NM 87131-0001, USA
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4
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Szafrańska PA, Andreasson F, Nord A, Nilsson JÅ. Deep body and surface temperature responses to hot and cold environments in the zebra finch. J Therm Biol 2020; 94:102776. [PMID: 33292974 DOI: 10.1016/j.jtherbio.2020.102776] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2020] [Revised: 10/26/2020] [Accepted: 10/29/2020] [Indexed: 10/23/2022]
Abstract
Global warming increasingly challenges thermoregulation in endothermic animals, particularly in hot and dry environments where low water availability and high temperature increase the risk of hyperthermia. In birds, un-feathered body parts such as the head and bill work as 'thermal windows', because heat flux is higher compared to more insulated body regions. We studied how such structures were used in different thermal environments, and if heat flux properties change with time in a given temperature. We acclimated zebra finches (Taeniopygia guttata) to two different ambient temperatures, 'cold' (5 °C) and 'hot' (35 °C), and measured the response in core body temperature using a thermometer, and head surface temperature using thermal imaging. Birds in the hot treatment had 10.3 °C higher head temperature than those in the cold treatment. Thermal acclimation also resulted in heat storage in the hot group: core body temperature was 1.1 °C higher in the 35 °C group compared to the 5 °C group. Hence, the thermal gradient from core to shell was 9.03 °C smaller in the hot treatment. Dry heat transfer rate from the head was significantly lower in the hot compared to the cold treatment after four weeks of thermal acclimation. This reflects constraints on changes to peripheral circulation and maximum body temperature. Heat dissipation capacity from the head region increased with acclimation time in the hot treatment, perhaps because angiogenesis was required to reach peak heat transfer rate. We have shown that zebra finches meet high environmental temperature by heat storage, which saves water and energy, and by peripheral vasodilation in the head, which facilitates dry heat loss. These responses will not exclude the need for evaporative cooling, but will lessen the amount of energy expend on body temperature reduction in hot environments.
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Affiliation(s)
- Paulina Anna Szafrańska
- Mammal Research Institute, Polish Academy of Sciences, Białowieża, Poland; Department of Biology, Lund University, Lund, Sweden.
| | | | - Andreas Nord
- Department of Biology, Lund University, Lund, Sweden.
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5
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Pessato A, McKechnie AE, Buchanan KL, Mariette MM. Vocal panting: a novel thermoregulatory mechanism for enhancing heat tolerance in a desert-adapted bird. Sci Rep 2020; 10:18914. [PMID: 33144650 PMCID: PMC7609653 DOI: 10.1038/s41598-020-75909-6] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Accepted: 10/15/2020] [Indexed: 01/06/2023] Open
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.
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Affiliation(s)
- Anaïs Pessato
- Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University Geelong, Geelong, VIC, 3216, Australia.
| | - Andrew E McKechnie
- South African Research Chair in Conservation Physiology, South African National Biodiversity Institute, Pretoria, 0001, South Africa.,DST-NRF Centre of Excellence at the FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria, 0001, South Africa
| | - Katherine L Buchanan
- Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University Geelong, Geelong, VIC, 3216, Australia
| | - Mylene M Mariette
- Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University Geelong, Geelong, VIC, 3216, Australia.
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6
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7
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Freeman MT, Czenze ZJ, Schoeman K, McKechnie AE. Extreme hyperthermia tolerance in the world's most abundant wild bird. Sci Rep 2020; 10:13098. [PMID: 32753751 PMCID: PMC7403380 DOI: 10.1038/s41598-020-69997-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2020] [Accepted: 06/26/2020] [Indexed: 11/09/2022] Open
Abstract
The thermal tolerances of vertebrates are generally restricted to body temperatures below 45–47 °C, and avian and mammalian critical thermal maxima seldom exceed 46 °C. We investigated thermoregulation at high air temperatures in the red-billed quelea (Quelea quelea), an African passerine bird that occurs in flocks sometimes numbering millions of individuals. Our data reveal this species can increase its body temperature to extremely high levels: queleas exposed to air temperature > 45 °C increased body temperature to 48.0 ± 0.7 °C without any apparent ill-effect, with individual values as high as 49.1 °C. These values exceed known avian lethal limits, with tolerance of body temperature > 48 °C unprecedented among birds and mammals.
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Affiliation(s)
- M T Freeman
- South African Research Chair in Conservation Physiology, South African National Biodiversity Institute, Pretoria, South Africa.,DSI-NRF Centre of Excellence at the FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa
| | - Z J Czenze
- South African Research Chair in Conservation Physiology, South African National Biodiversity Institute, Pretoria, South Africa.,DSI-NRF Centre of Excellence at the FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa
| | - K Schoeman
- South African Research Chair in Conservation Physiology, South African National Biodiversity Institute, Pretoria, South Africa.,DSI-NRF Centre of Excellence at the FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa
| | - A E McKechnie
- South African Research Chair in Conservation Physiology, South African National Biodiversity Institute, Pretoria, South Africa. .,DSI-NRF Centre of Excellence at the FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Pretoria, South Africa.
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8
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Ruth JM, Talbot WA, Smith EK. Behavioral Response to High Temperatures in a Desert Grassland Bird: Use of Shrubs as Thermal Refugia. WEST N AM NATURALIST 2020. [DOI: 10.3398/064.080.0215] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Affiliation(s)
- Janet M. Ruth
- U.S. Geological Survey, Fort Collins Science Center, New Mexico Landscapes Field Station, Albuquerque, NM 87131
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9
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Bat thermoregulation in the heat: Limits to evaporative cooling capacity in three southern African bats. J Therm Biol 2020; 89:102542. [PMID: 32364970 DOI: 10.1016/j.jtherbio.2020.102542] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2019] [Revised: 02/07/2020] [Accepted: 02/13/2020] [Indexed: 12/16/2022]
Abstract
High environmental temperatures pose significant physiological challenges related to energy and water balance for small endotherms. Although there is a growing literature on the effect of high temperatures on birds, comparable data are scarcer for bats. Those data that do exist suggest that roost microsite may predict tolerance of high air temperatures. To examine this possibility further, we quantified the upper limits to heat tolerance and evaporative cooling capacity in three southern African bat species inhabiting the same hot environment but using different roost types (crevice, foliage or cave). We used flow-through respirometry and compared heat tolerance limits (highest air temperature (Ta) tolerated before the onset of severe hyperthermia), body temperature (Tb), evaporative water loss, metabolic rate, and maximum cooling capacity (i.e., evaporative heat loss/metabolic heat production). Heat tolerance limits for the two bats roosting in more exposed sites, Taphozous mauritianus (foliage-roosting) and Eptesicus hottentotus (crevice-roosting), were Ta = ~44 °C and those individuals defended maximum Tb between 41 °C and 43 °C. The heat tolerance limit for the bat roosting in a more buffered site, Rousettus aegyptiacus (cave-roosting), was Ta = ~38 °C with a corresponding Tb of ~38 °C. These interspecific differences, together with a similar trend for higher evaporative cooling efficiency in species occupying warmer roost microsites, add further support to the notion that ecological factors like roost choice may have profound influences on physiological traits related to thermoregulation.
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10
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Škop V, Guo J, Liu N, Xiao C, Hall KD, Gavrilova O, Reitman ML. Mouse Thermoregulation: Introducing the Concept of the Thermoneutral Point. Cell Rep 2020; 31:107501. [PMID: 32294435 PMCID: PMC7243168 DOI: 10.1016/j.celrep.2020.03.065] [Citation(s) in RCA: 85] [Impact Index Per Article: 21.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2019] [Revised: 11/18/2019] [Accepted: 03/19/2020] [Indexed: 12/21/2022] Open
Abstract
Human and mouse thermal physiology differ due to dissimilar body sizes. Unexpectedly, in mice we found no ambient temperature zone where both metabolic rate and body temperature were constant. Body temperature began increasing once cold-induced thermogenesis was no longer required. This result reproduced in male, female, C57BL/6J, 129, chow-fed, diet-induced obese, and ob/ob mice as well as Trpv1-/-;Trpm8-/-;Trpa1-/- mice lacking thermal sensory channels. During the resting-light phase, the energy expenditure minimum spanned ∼4°C of ambient temperature, whereas in the active-dark phase it approximated a point. We propose the concept of a thermoneutral point (TNP), a discrete ambient temperature below which energy expenditure increases and above which body temperature increases. Humans do not have a TNP. As studied, the mouse TNP is ∼29°C in light phase and ∼33°C in dark phase. These observations inform how thermoneutrality is defined and how mice are used to model human energy physiology and drug development.
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Affiliation(s)
- Vojtěch Škop
- Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA
| | - Juen Guo
- Laboratory of Biological Modeling, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA
| | - Naili Liu
- Mouse Metabolism Core, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA
| | - Cuiying Xiao
- Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA
| | - Kevin D Hall
- Laboratory of Biological Modeling, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA
| | - Oksana Gavrilova
- Mouse Metabolism Core, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA
| | - Marc L Reitman
- Diabetes, Endocrinology, and Obesity Branch, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, MD 20892, USA.
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11
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McKechnie AE, Wolf BO. The Physiology of Heat Tolerance in Small Endotherms. Physiology (Bethesda) 2020; 34:302-313. [PMID: 31389778 DOI: 10.1152/physiol.00011.2019] [Citation(s) in RCA: 77] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
Understanding the heat tolerances of small mammals and birds has taken on new urgency with the advent of climate change. Here, we review heat tolerance limits, pathways of evaporative heat dissipation that permit the defense of body temperature during heat exposure, and mechanisms operating at tissue, cellular, and molecular levels.
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Affiliation(s)
- Andrew E McKechnie
- South African Research Chair in Conservation Physiology, National Zoological Garden, South African National Biodiversity Institute, Pretoria, South Africa.,DST-NRF Centre of Excellence at the FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Hatfield, South Africa
| | - Blair O Wolf
- UNM Biology Department, University of New Mexico, Albuquerque, New Mexico
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12
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Conradie SR, Woodborne SM, Wolf BO, Pessato A, Mariette MM, McKechnie AE. Avian mortality risk during heat waves will increase greatly in arid Australia during the 21st century. CONSERVATION PHYSIOLOGY 2020; 8:coaa048. [PMID: 32523698 PMCID: PMC7271765 DOI: 10.1093/conphys/coaa048] [Citation(s) in RCA: 38] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2020] [Revised: 04/15/2020] [Accepted: 05/03/2020] [Indexed: 05/05/2023]
Abstract
Intense heat waves are occurring more frequently, with concomitant increases in the risk of catastrophic avian mortality events via lethal dehydration or hyperthermia. We quantified the risks of lethal hyperthermia and dehydration for 10 Australian arid-zone avifauna species during the 21st century, by synthesizing thermal physiology data on evaporative water losses and heat tolerance limits. We evaluated risks of lethal hyperthermia or exceedance of dehydration tolerance limits in the absence of drinking during the hottest part of the day under recent climatic conditions, compared to those predicted for the end of this century across Australia. Increases in mortality risk via lethal dehydration and hyperthermia vary among the species modelled here but will generally increase greatly, particularly in smaller species (~10-42 g) and those inhabiting the far western parts of the continent. By 2100 CE, zebra finches' potential exposure to acute lethal dehydration risk will reach ~ 100 d y-1 in the far northwest of Australia and will exceed 20 d y-1 over > 50% of this species' current range. Risks of dehydration and hyperthermia will remain much lower for large non-passerines such as crested pigeons. Risks of lethal hyperthermia will also increase substantially for smaller species, particularly if they are forced to visit exposed water sources at very high air temperatures to avoid dehydration. An analysis of atlas data for zebra finches suggests that population declines associated with very hot conditions are already occurring in the hottest areas. Our findings suggest that the likelihood of persistence within current species ranges, and the potential for range shifts, will become increasingly constrained by temperature and access to drinking water. Our model adds to an increasing body of literature suggesting that arid environments globally will experience considerable losses of avifauna and biodiversity under unmitigated climate change scenarios.
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Affiliation(s)
- Shannon R Conradie
- South African Research Chair in Conservation Physiology, South African National Biodiversity Institute, 2 Cussonia Ave, Brummeria, Pretoria 0184, South Africa
- DST-NRF Centre of Excellence at the FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Lynnwood Rd., Pretoria 0002, South Africa
| | - Stephan M Woodborne
- iThemba LABS, Johannesburg, 514 Empire Rd, Johannesburg 2193, South Africa
- Mammal Research Institute, University of Pretoria, Lynnwood Rd., Pretoria 0002, South Africa
| | - Blair O Wolf
- UNM Biology Department, University of New Mexico, Albuquerque, NM 87131, U.S.A
| | - Anaïs Pessato
- Centre for Integrative Ecology, School of Life & Environmental Sciences, Deakin University, 75 Pigdons Road, Waurn Ponds VIC 3216, Australia
| | - Mylene M Mariette
- Centre for Integrative Ecology, School of Life & Environmental Sciences, Deakin University, 75 Pigdons Road, Waurn Ponds VIC 3216, Australia
| | - Andrew E McKechnie
- South African Research Chair in Conservation Physiology, South African National Biodiversity Institute, 2 Cussonia Ave, Brummeria, Pretoria 0184, South Africa
- DST-NRF Centre of Excellence at the FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Lynnwood Rd., Pretoria 0002, South Africa
- Corresponding author: South African Research Chair in Conservation Physiology, South African National Biodiversity Institute, South Africa.
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13
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Chronic, sublethal effects of high temperatures will cause severe declines in southern African arid-zone birds during the 21st century. Proc Natl Acad Sci U S A 2019; 116:14065-14070. [PMID: 31235571 DOI: 10.1073/pnas.1821312116] [Citation(s) in RCA: 91] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Birds inhabiting hot, arid regions are among the terrestrial organisms most vulnerable to climate change. The potential for increasingly frequent and intense heat waves to cause lethal dehydration and hyperthermia is well documented, but the consequences of sublethal fitness costs associated with chronic exposure to sustained hot weather remain unclear. Using data for species occurring in southern Africa's Kalahari Desert, we mapped exposure to acute lethal risks and chronic sublethal fitness costs under past, present, and future climates. For inactive birds in shaded microsites, the risks of lethal dehydration and hyperthermia will remain low during the 21st century. In contrast, exposure to conditions associated with chronic, sublethal costs related to progressive body mass loss, reduced nestling growth rates, or increased breeding failure will expand dramatically. For example, by the 2080s the region will experience 10-20 consecutive days per year on which Southern Pied Babblers (Turdoides bicolor) will lose ∼4% of body mass per day, conditions under which this species' persistence will be extremely unlikely. Similarly, exposure to air temperature maxima associated with delayed fledging, reduced fledgling size, and breeding failure will increase several-fold in Southern Yellow-billed Hornbills (Tockus leucomelas) and Southern Fiscals (Lanius collaris). Our analysis reveals that sublethal costs of chronic heat exposure are likely to drive large declines in avian diversity in the southern African arid zone by the end of the century.
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14
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le Roux CE, McFarlane Tranquilla LA, Nocera JJ. Ambient temperature preferences of chimney swifts (Chaetura pelagica) for Nest Site Selection. J Therm Biol 2019; 80:89-93. [PMID: 30784493 DOI: 10.1016/j.jtherbio.2018.12.017] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2018] [Revised: 12/14/2018] [Accepted: 12/16/2018] [Indexed: 10/27/2022]
Abstract
Chimney swift (Chaetura pelagica) populations are declining rapidly, with no clear indication as to why. Reduced availability of nesting habitat (chimneys) was thought to be a limiting factor for this threatened species, but data from Ontario, Canada did not support this hypothesis. If availability is not limiting, then perhaps habitat quality may play a role. We examined the thermal aspect of chimneys that are used by nesting swifts. To do so, we identified upper and lower thermal limits influencing the selection of chimneys for nesting. Across Nova Scotia and New Brunswick, we deployed temperature loggers in 19 chimneys, 11 of which contained chimney swift nests and 8 that were deemed suitable for nesting but were not occupied. Temperature readings were recorded at 30-min intervals from 23 June to 15 September 2017. We found that chimney occupancy by swifts was negatively correlated with maximum and mean chimney temperature. We did not find a relationship between occupancy and minimum temperature, temperature fluctuations, or chimney material. These results indicate that chimney swifts are preferentially selecting cooler chimneys for nesting.
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Affiliation(s)
- Courtney E le Roux
- University of New Brunswick, 3 Bailey Drive, Fredericton, New Brunswick, Canada E3B 5A3.
| | | | - Joseph J Nocera
- University of New Brunswick, 3 Bailey Drive, Fredericton, New Brunswick, Canada E3B 5A3
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15
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Gerson AR, McKechnie AE, Smit B, Whitfield MC, Smith EK, Talbot WA, McWhorter TJ, Wolf BO. The functional significance of facultative hyperthermia varies with body size and phylogeny in birds. Funct Ecol 2019. [DOI: 10.1111/1365-2435.13274] [Citation(s) in RCA: 44] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Affiliation(s)
| | - Andrew E. McKechnie
- South African Research Chair in Conservation Physiology, National Zoological Garden South African National Biodiversity Institute Pretoria South Africa
- DST‐NRF Centre of Excellence at the FitzPatrick InstituteDepartment of Zoology and Entomology University of Pretoria Hatfield South Africa
| | - Ben Smit
- DST‐NRF Centre of Excellence at the FitzPatrick InstituteDepartment of Zoology and Entomology Rhodes University Grahamstown South Africa
| | - Maxine C. Whitfield
- DST‐NRF Centre of Excellence at the FitzPatrick InstituteDepartment of Zoology and Entomology University of Pretoria Hatfield South Africa
| | - Eric K. Smith
- Department of Biology University of New Mexico Albuquerque New Mexico
| | - William A. Talbot
- Department of Biology University of New Mexico Albuquerque New Mexico
| | - Todd J. McWhorter
- School of Animal and Veterinary Sciences University of Adelaide Adelaide South Australia Australia
| | - Blair O. Wolf
- Department of Biology University of New Mexico Albuquerque New Mexico
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16
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Kemp R, McKechnie AE. Thermal physiology of a range-restricted desert lark. J Comp Physiol B 2018; 189:131-141. [PMID: 30488103 DOI: 10.1007/s00360-018-1190-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2018] [Revised: 10/27/2018] [Accepted: 11/05/2018] [Indexed: 11/30/2022]
Abstract
Much recent work on avian physiological adaptation to desert environments has focused on larks (Passeriformes: Alaudidae). We tested the prediction that the threatened red lark (Calendulauda burra), a species restricted to very arid parts of South Africa and which is not known to drink, exhibits highly efficient evaporative cooling and makes pronounced use of facultative hyperthermia when exposed to high air temperatures (Ta). We also predicted that C. burra possesses similarly low basal metabolic rate (BMR) and total evaporative water loss (EWL) at moderate Ta as reported for species from the deserts of the Middle East. Rest-phase thermoregulation in C. burra was characterized by an unusually low lower critical limit of thermoneutrality at Ta = ~ 21 °C and a BMR of 0.317 ± 0.047 W, the lowest BMR relative to allometrically-expected values yet reported in any lark. During the diurnal active phase, red larks were able to tolerate Ta up to 50 °C, with the onset of panting occurring at Ta = 38 °C. Maximum EWL was 1.475 ± 0.107 g h- 1 at Ta = 50 °C, equivalent to 620% of minimum EWL at thermoneutrality. The maximum ratio of evaporative heat dissipation to metabolic heat production was 1.58, a value towards the lower end of the range reported for passerines. Our data support the prediction that C. burra shows metabolic traits similar to those of other larks inhabiting extremely arid climates, but not the notion that evaporative cooling at high Ta in this species is more efficient than in most passerines.
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Affiliation(s)
- Ryno Kemp
- DST-NRF Centre of Excellence at the FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Hatfield, Private Bag X20, Pretoria, 0028, South Africa
- South African Research Chair in Conservation Physiology, National Zoological Garden, South African National Biodiversity Institute, P.O. Box 754, Pretoria, 0001, South Africa
| | - Andrew E McKechnie
- DST-NRF Centre of Excellence at the FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Hatfield, Private Bag X20, Pretoria, 0028, South Africa.
- South African Research Chair in Conservation Physiology, National Zoological Garden, South African National Biodiversity Institute, P.O. Box 754, Pretoria, 0001, South Africa.
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McWhorter TJ, Gerson AR, Talbot WA, Smith EK, McKechnie AE, Wolf BO. Avian thermoregulation in the heat: evaporative cooling capacity and thermal tolerance in two Australian parrots. ACTA ACUST UNITED AC 2018; 221:jeb.168930. [PMID: 29440360 DOI: 10.1242/jeb.168930] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2017] [Accepted: 02/01/2018] [Indexed: 11/20/2022]
Abstract
Avian orders differ in their thermoregulatory capabilities and tolerance of high environmental temperatures. Evaporative heat loss, and the primary avenue whereby it occurs, differs amongst taxa. Although Australian parrots (Psittaciformes) have been impacted by mass mortality events associated with extreme weather events (heat waves), their thermoregulatory physiology has not been well characterized. We quantified the upper limits to thermoregulation under extremely hot conditions in two Australian parrots: the mulga parrot (Psephotellus varius; ∼55 g) and the galah (Eolophus roseicapilla; ∼265 g). At air temperatures (Ta) exceeding body temperature (Tb), both species showed increases in Tb to maximum values around 43-44°C, accompanied by rapid increases in resting metabolic rate above clearly defined upper critical limits of thermoneutrality and increases in evaporative water loss to levels equivalent to 700-1000% of baseline rates at thermoneutral Ta Maximum cooling capacity, quantified as the fraction of metabolic heat production dissipated evaporatively, ranged from 1.71 to 1.79, consistent with the known range for parrots, similar to the corresponding range in passerines, and well below the corresponding ranges for columbids and caprimulgids. Heat tolerance limit (the maximum Ta tolerated) ranged from 44 to 55°C, similar to the range reported for passerines, but lower than that reported for columbids and caprimulgids. Our data suggest that heat tolerance in parrots is similar to that in passerines. We argue that understanding how thermoregulatory capacity and heat tolerance vary across avian orders is vital for predicting how climate change and the associated increase in frequency of extreme weather events may impact avian populations in the future.
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Affiliation(s)
- Todd J McWhorter
- School of Animal & Veterinary Sciences, University of Adelaide, Roseworthy Campus, South Australia 5371, Australia
| | - Alexander R Gerson
- Department of Biology, University of Massachusetts, Amherst, MA 01003, USA
| | - William A Talbot
- Department of Biology, University of New Mexico, MSC03-2020, Albuquerque, NM 87131-0001, USA
| | - Eric Krabbe Smith
- Department of Biology, University of New Mexico, MSC03-2020, Albuquerque, NM 87131-0001, USA
| | - Andrew E McKechnie
- DST-NRF Centre of Excellence at the Percy FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa.,South African Research Chair in Conservation Physiology, National Zoological Gardens of South Africa, P.O. Box 754, Pretoria 0001, South Africa
| | - Blair O Wolf
- Department of Biology, University of New Mexico, MSC03-2020, Albuquerque, NM 87131-0001, USA
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18
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Smit B, Whitfield MC, Talbot WA, Gerson AR, McKechnie AE, Wolf BO. Avian thermoregulation in the heat: phylogenetic variation among avian orders in evaporative cooling capacity and heat tolerance. ACTA ACUST UNITED AC 2018; 221:jeb.174870. [PMID: 29440359 DOI: 10.1242/jeb.174870] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2017] [Accepted: 02/01/2018] [Indexed: 11/20/2022]
Abstract
Little 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, namely, the 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 and evaporative water loss increased by quantitatively similar magnitudes in all three species, although maximum rates of evaporative water loss 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.
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Affiliation(s)
- Ben Smit
- Department of Zoology and Entomology, Rhodes University, P.O. Box 94, Grahamstown 6040, South Africa
| | - Maxine C Whitfield
- DST-NRF Centre of Excellence at the Percy FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa
| | - William A Talbot
- UNM Biology Department, University of New Mexico, MSC03-2020, Albuquerque, NM 87131-0001, USA
| | - Alexander R Gerson
- Department of Biology, University of Massachusetts, Amherst, MA 01003, USA
| | - Andrew E McKechnie
- DST-NRF Centre of Excellence at the Percy FitzPatrick Institute, Department of Zoology and Entomology, University of Pretoria, Private Bag X20, Hatfield 0028, South Africa.,South African Research Chair in Conservation Physiology, National Zoological Gardens of South Africa, P.O. Box 754, Pretoria 0001, South Africa
| | - Blair O Wolf
- UNM Biology Department, University of New Mexico, MSC03-2020, Albuquerque, NM 87131-0001, USA
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