Environmental determinants of total evaporative water loss in birds at multiple temperatures

Abstract Endotherms dissipate heat to the environment to maintain a stable body temperature at high ambient temperatures, which requires them to maintain a balance between heat dissipation and water conservation. Birds are relatively small, contain a large amount of metabolically expensive tissue, and are mostly diurnal, making them susceptible to physiological challenges related to water balance and heat dissipation. We compiled total evaporative water loss (TEWL) measurements for 174 species of birds exposed to different temperatures and used comparative methods to examine their relationships with body size, ambient temperature, precipitation, diet, and diel activity cycle. TEWL in the thermoneutral zone (TNZ) was associated primarily with body mass and activity phase. Larger and more active-phase birds, with their higher metabolic rates, lost more water through evaporation than smaller, resting-phase birds, particularly at higher thermal exposures. However, maximum temperature of the natural habitat became an important determinant of TEWL when birds were exposed to temperatures exceeding the TNZ. Species from hotter climates exhibited higher TEWL. Adaptation to arid climates did not restrict evaporative water loss at thermal conditions within the TNZ, but promoted evaporative water loss at exposures above the TNZ. The TEWL of granivores, which ingest food with low water content, differed little from species with other food habitats under all thermal conditions. The effects of environmental covariates of TEWL were dissimilar across thermal exposures, suggesting no evidence for a tradeoff between water conservation in the TNZ and heat dissipation at exposure to higher temperatures. Thus, birds may be able to acclimate when climate change results in the need to increase heat dissipation due to warming, except perhaps in hot, arid environments where species will need to depend heavily upon evaporative cooling to maintain homeothermy.

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Studies of the environmental physiology of tropical merinos

Australian Journal of Agricultural Research ◽

10.1071/ar9780161 ◽

1978 ◽

Vol 29 (1) ◽

pp. 161 ◽

Cited By ~ 18

Author(s):

PS Hopkins ◽

GI Knights ◽

AS Le Feuvre

Keyword(s):

Low Temperature ◽

Rectal Temperature ◽

Water Loss ◽

Heat Dissipation ◽

Evaporative Water Loss ◽

Compensatory Mechanisms ◽

Evaporative Water ◽

Ambient Temperatures ◽

Diurnal Patterns ◽

Made In

Rectal temperature measurements of tropical Merino sheep taken in the sun during summer indicated that there were high and low temperature groups. Animals of low temperature status (e.g. 39.4°C) also exhibited a low respiration rate (e.g. 110/min) in comparison with their less adapted counterparts (40.0° and 190/min). These differences were greatest when ambient temperatures were high. The repeatability of temperature status was 0.46 (P < 0.01). Animals of folds (+) phenotype had significantly higher rectal temperatures than folds (–) animals (P < 0.05). Shearing caused a marked but transient increase in rectal temperature. Compensatory mechanisms apparently involved an increase in cutaneous heat dissipation and/or a decrease in exogenous heat load. Evaporative water loss (80–115 ml/kg/day) greatly exceeded the non-evaporative water loss (40–65 ml/kg/day) of sheep in metabolism cages. Respiratory water loss could account for only 8–10% of the total daily evaporative water loss. Non-respiratory evaporative water loss (as measured by difference) was c. 75–100 ml/kg/day. There were no striking differences between high and low temperature status sheep in this regard. Measurements of respiratory (2 ml/kg/hr) and non-respiratory (5.5 ml/kg/hr) evaporative water loss made in hygrometric tents suggested that the greater non-respiratory water loss was partly due to a higher rate of loss and partly to a longer period of loss per day. This suggestion was supported by the diurnal patterns of rectal temperatures and respiration rates reported here, though no firm conclusions could be made as to the thermotaxic effect of non-respiratory water loss and thermoregulation of tropical Merinos with varying amounts of wool cover.

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Evaporative Water Loss in Desert Rodents in Their Natural Habitat

Ecology ◽

10.2307/1931362 ◽

1950 ◽

Vol 31 (1) ◽

pp. 75-85 ◽

Cited By ~ 59

Author(s):

Bodil Schmidt-Nielsen ◽

Knut Schmidt-Nielsen

Keyword(s):

Water Loss ◽

Natural Habitat ◽

Evaporative Water Loss ◽

Evaporative Water ◽

Desert Rodents

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Does control of insensible evaporative water loss by two species of mesic parrot have a thermoregulatory role?

Journal of Experimental Biology ◽

10.1242/jeb.229930 ◽

2020 ◽

Vol 223 (19) ◽

pp. jeb229930 ◽

Cited By ~ 1

Author(s):

Christine Elizabeth Cooper ◽

Philip Carew Withers ◽

Gerhard Körtner ◽

Fritz Geiser

Keyword(s):

Water Loss ◽

Water Conservation ◽

Arid Zone ◽

Evaporative Water Loss ◽

Primary Role ◽

Physiological Control ◽

Evaporative Water ◽

Ambient Temperatures ◽

Physiological Variables ◽

Regulatory Ability

ABSTRACTInsensible evaporative water loss (EWL) at or below thermoneutrality is generally assumed to be a passive physical process. However, some arid zone mammals and a single arid zone bird can control their insensible water loss, so we tested the hypothesis that the same is the case for two parrot species from a mesic habitat. We investigated red-rumped parrots (Psephotus haematonotus) and eastern rosellas (Platycercus eximius), measuring their EWL, and other physiological variables, at a range of relative humidities at ambient temperatures of 20 and 30°C (below and at thermoneutrality). We found that, despite a decrease in EWL with increasing relative humidity, rates of EWL were not fully accounted for by the water vapour deficit between the animal and its environment, indicating that the insensible EWL of both parrots was controlled. It is unlikely that this deviation from physical expectations was regulation with a primary role for water conservation because our mesic-habitat parrots had equivalent regulatory ability as the arid habitat budgerigar (Melopsittacus undulatus). This, together with our observations of body temperature and metabolic rate, instead support the hypothesis that acute physiological control of insensible water loss serves a thermoregulatory purpose for endotherms. Modification of both cutaneous and respiratory avenues of evaporation may be involved, possibly via modification of expired air temperature and humidity, and surface resistance.

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Respiratory and cutaneous evaporative water loss at high environmental temperatures in a small bird

Journal of Experimental Biology ◽

10.1242/jeb.199.2.451 ◽

1996 ◽

Vol 199 (2) ◽

pp. 451-457 ◽

Cited By ~ 18

Author(s):

B Wolf ◽

G Walsberg

Keyword(s):

Metabolic Rate ◽

Air Temperature ◽

Water Loss ◽

Heat Dissipation ◽

Evaporative Water Loss ◽

Co2 Production ◽

Evaporative Heat Loss ◽

Evaporative Water ◽

Metabolic Chamber ◽

Air Temperatures

We measured rates of respiratory and cutaneous evaporative water loss as a function of air temperature in a small desert bird, the verdin Auriparus flaviceps. Birds were placed in a two-compartment metabolic chamber that separately collected water evaporated from the bird's head and body. Cutaneous and respiratory evaporative water loss, as well as CO2 production, were measured in resting birds at 2 °C intervals between 30 and 50 °C. Metabolic rate was lowest at 38 °C (19 mW g-1) and increased to 28 mW g-1 at 50 °C. At the lowest air temperature, 30 °C, resting metabolic rate was 34 mW g-1. As air temperature increased from 30 to 50 °C, cutaneous water loss increased from 3.3 to 10.3 mg g-1 h-1 and respiratory water loss increased from 2.1-64.1 mg g-1 h-1. At moderate air temperatures (30-36 °C), water loss was divided almost evenly between respiratory and cutaneous components. As air temperature increased, however, verdins became heavily dependent on respiratory evaporation for heat dissipation. Evaporative water loss data for other species at high air temperatures suggest that partitioning of water loss may follow two different patterns. Evaporative heat dissipation may depend primarily on either cutaneous or respiratory modes of evaporative heat transfer. The physiological mechanisms and functional significance of these contrasting patterns of evaporative heat loss remain unknown.

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Incorporating evaporative water loss into bioenergetic models of hibernation to test for relative influence of host and pathogen traits on white-nose syndrome

10.1101/750257 ◽

2019 ◽

Author(s):

Catherine G. Haase ◽

Nathan W. Fuller ◽

C. Reed Hranac ◽

David T. S. Hayman ◽

Liam P. McGuire ◽

...

Keyword(s):

Water Loss ◽

Water Conservation ◽

Fungal Growth ◽

Host Adaptation ◽

Evaporative Water Loss ◽

Myotis Lucifugus ◽

Evaporative Water ◽

White Nose Syndrome ◽

Animal Physiology ◽

Fat Stores

AbstractHibernation consists of extended durations of torpor interrupted by periodic arousals. The ‘dehydration hypothesis’ proposes that hibernating mammals arouse to replenish water lost through evaporation during torpor. Arousals are energetically expensive, and increased arousal frequency can alter survival throughout hibernation. Yet we lack a means to assess the effect of evaporative water loss (EWL), determined by animal physiology and hibernation microclimate, on torpor bout duration and subsequent survival. White-nose syndrome (WNS), a devastating disease impacting hibernating bats, causes increased frequency of arousals during hibernation and EWL has been hypothesized to contribute to this increased arousal frequency. WNS is caused by a fungus, which grows well in humid hibernaculum environments and damages wing tissue important for water conservation. Here, we integrated the effect of EWL on torpor expression in a hibernation energetics model, including the effects of fungal infection, to determine the link between EWL and survival. We collected field data for Myotis lucifugus, a species that experiences high mortality from WNS, to gather parameters for the model. In saturating conditions we predicted healthy bats experience minimal mortality. Infected bats, however, suffer high fungal growth in highly saturated environments, leading to exhaustion of fat stores before spring. Our results suggest that host adaptation to humid environments leads to increased arousal frequency from infection, which drives mortality across hibernaculum conditions. Our modified hibernation model provides a tool to assess the interplay between host physiology, hibernaculum microclimate, and diseases such as WNS on winter survival.

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