Water and energy fluxes during summer in an arid-zone passerine bird

Endothermic animals resident in hot, arid terrestrial environments are likely to face a tradeoff between their ability to obtain water and elevated thermoregulatory water requirements. We assessed whether daily water flux (DWF) is higher on hot days, reflecting increases in evaporative cooling demands, in an arid-zone bird that obtains its water through food intake. We obtained measurements of DWF (partitioned into water influx and efflux rates) in 71 White-browed Sparrow-Weavers Plocepasser mahali at a desert site and a semi-desert site, during summer in the Kalahari Desert of southern Africa. We found no evidence that DWF varied with maximum daily air temperature (Tair, range = 27.6–39.2 °C). Instead, DWF was lower during dry periods than in the wet season at the semi-desert site. Furthermore, birds showed deficits in water balance (water influx/water efflux) during the dry periods at both sites. Our data show that DWF is low in a non-drinking bird that obtains its water through food, and that demands for evaporative water loss on very hot days (maximum Tair of 40–44 °C) may exceed water intake rates during hot and dry periods. Species that do not have opportu-nities to drink will experience strong trade-offs between thermoregulation, hydration state and activity levels as temperatures increase.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1474-919X2016-10-31hb201

Global patterns of seasonal acclimatization in avian resting metabolic rates

The adjustment of resting metabolic rates represents an important component of avian seasonal acclimatization, with recent studies revealing substantial differences between summer and winter in birds from a wide range of latitudes. We compared seasonal variation in basal metabolic rate (BMR) and summit metabolism (Msum) between temperate and tropical/subtropical latitudes, and examined correlations with latitude and temperature. The direction and magnitude of seasonal adjustments in BMR are broadly related to temperature and latitude, but are significantly more variable among tropical and subtropical species compared to those inhabiting temperate zones. Winter adjustments in BMR among subtropical species, when expressed relative to summer values, range from decreases of approximately 35 % to increases of more than 60 %, whereas the majority of temperate-zone species show increases in BMR during winter. Relatively few seasonal Msum data exist for tropical/subtropical species, but those that are available involve responses ranging from winter decreases to increases of similar magnitude to those characteristic of many temperate-zone species. Recent studies also highlight the substantial variation in seasonal adjustments that may occur within species, and reiterate the need for further investigations of the relative roles of environmental variables such as temperature and food availability as determinants of seasonal metabolic variation.http://link.springer.com/journal/103362016-12-30hb201

Differences in the use of surface water resources by desert birds are revealed using isotopic tracers

The scarcity of free-standing water sources is a key determinant of animal and plant community structure in arid environments, and an understanding of the extent to which particular species use surface water is vital for modeling the effects of climate change on desert avifauna. We investigated interspecific variation in the use of artificial water sources among birds in the Kalahari Desert, South Africa, by (i) observations at waterholes and (ii) tracing spatial water-use patterns during summer by isotopically labeled water sources and blood sampling. More than 50% of the avian community (primarily insectivores and omnivores) were not observed to drink. The majority (53%) of species drinking at waterholes were granivorous, and their use of surface water was best predicted by their relative abundance in the community. Species representing the remaining dietary guilds drank significantly more on hot days. Blood samples revealed that only 11 of 42 species (mostly granivores and a few omnivores) showed evidence of drinking at a waterhole with enriched deuterium values; on average, in the latter birds, water from the enriched waterhole accounted for ~38% of their body water pool. These findings illustrate that 2 methods employed in this study provide different, but complementary data on the relative importance of a water source for an avian community. Although our results suggest that most avian species are independent of surface water, drinking patterns on the hottest days during our study period suggest that free-standing water might become more important for some of the non-drinking species under hotter climatic conditions

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

Many birds can defend body temperature (Tb) far below air temperature (Ta) during acute heat exposure, but relatively little is known about how avian heat tolerance and evaporative cooling capacity varies with body mass (Mb), phylogeny or ecological factors. We determined maximum rates of evaporative heat dissipation and thermal end points (Tb and Ta associated with thermoregulatory failure) in three southern African ploceid passerines, the scalyfeathered weaver (Sporopipes squamifrons, Mb≈10 g), sociable weaver (Philetairus socius, Mb≈25 g) and white-browed sparrowweaver (Plocepasser mahali, Mb≈40 g). Birds were exposed to a ramped profile of progressively increasing Ta, with continuous monitoring of behaviour and Tb used to identify the onset of severe hyperthermia. The maximum Ta birds tolerated ranged from 48°C to 54°C, and was positively related to Mb. Values of Tb associated with severe heat stress were in the range of 44 to 45°C. Rates of evaporative water loss (EWL) increased rapidly when Ta exceeded Tb, and maximum evaporative heat dissipation was equivalent to 141–222% of metabolic heat production. Fractional increases in EWL between Ta<40°C and the highest Ta reached by each species were 10.8 (S. squamifrons), 18.4 (P. socius) and 16.0 (P. mahali). Resting metabolic rates increased more gradually with Ta than expected, probably reflecting the very low chamber humidity values we maintained. Our data suggest that, within a taxon, larger species can tolerate higher Ta during acute heat stress.National Science Foundation under IOS-1122228http://jeb.biologists.org2016-06-30hb2016Zoology and Entomolog

Adaptive thermoregulation during summer in two populations of an arid-zone passerine

Heterothermy plays an important role in lowering the costs of thermoregulation in endotherms by reducing water and energy requirements. We tested predictions that birds in arid habitats should express fine-scale variation in their thermoregulatory patterns as a function of prevailing climatic conditions. We assessed effects of air temperature (Tair) and water vapor pressure deficit (D) on body temperature (Tb) in free-living White-browed Sparrow-Weavers (Plocepasser mahali) during summer in two arid habitats in the Kalahari Desert, South Africa, using data from a dry period at a hot, desert site (n ¼ 7 birds), and during a dry period (n¼4 birds) and a wet period (n¼5 birds) at a milder, semi-desert site. The desert birds maintained a significantly higher set-point Tb (41.58 6 0.28C, mean 6 SD) than semi-desert birds (40.28 6 0.28C). During the warmest part of day (12:00–18:00 hours), Tb increased significantly during periods of high Tair and/or high humidity, and mean and maximum Tb were up to 1.48 and 2.38C, respectively, above normal levels. However, as Tair increased, birds at the desert site maintained Tb at or below set-point levels for a greater proportion of the time than birds at the semi-desert site. Birds at the desert site also expressed a greater magnitude of daily heterothermy (heterothermy index, HI ¼ 2.48 6 0.38C, mean 6 SD) than birds at the semi-desert site: the latter population showed a greater magnitude of heterothermy during a dry period (HI ¼ 2.18 6 0.38C) than during a wet period (HI ¼ 1.68 6 0.28C). Birds continued foraging throughout the warmest part of the day, despite the fact that heat dissipation (percentage of time spent panting and wing-spreading) increased significantly with increasing Tair. Our findings reveal that populations can vary in their thermoregulatory responses in both space and time and suggest that small changes in Tair can have significant effects on thermoregulation in free-ranging desert birds, even when Tair , Tb. These data have important implications for assessing vulnerability of species to climate change, suggesting that sensitivity should be assessed at the population, rather than species, level.The DST/ NRF Centre of Excellence at the Percy FitzPatrick Institute, and a Sigma XI Grant in Aid of Research to B. Smit.http://www.esajournals.org/loi/ecol?am201

Thermoregulation in African green pigeons (Treron calvus) and a re-analysis of insular effects on basal metabolic rate and heterothermy in columbid birds

Columbid birds represent a useful model taxon for examining adaptation in metabolic and thermal traits, including the effects of insularity. To test predictions concerning the role of insularity and low predation risk as factors selecting for the use of torpor, and the evolution of low basal metabolic rate in island species, we examined thermoregulation under laboratory and semi-natural conditions in a mainland species, the African Green-Pigeon (Treron calvus). Under laboratory conditions, rest-phase body temperature (Tb) was significantly and positively correlated with air temperature (Ta) between 0 °C and 35 °C, and the relationship between resting metabolic rate (RMR) and Ta differed from typical endothermic patterns. The minimum RMR, which we interpret as basal metabolic rate (BMR), was 0.825 ± 0.090 W. Green-pigeons responded to food restriction by significantly decreasing rest-phase Tb, but the reductions were small (at most ~ 5 °C below normothermic values), with a minimum Tb of 33.1 °C recorded in a food-deprived bird. We found no evidence of the large reductions in Tb and metabolic rate and the lethargic state characteristic of torpor. The absence of torpor in T. calvus lends support to the idea that species restricted to islands that are free of predators are more likely to use torpor than mainland species that face the risk of predation during the rest-phase. We also analysed interspecific variation in columbid BMR in a phylogenetically-informed framework, and verified the conclusions of an earlier study that found that BMR is significantly lower in island species compared to those that occur on mainlands.DST/NRF Centre of Excellence at the Percy FitzPatrick Institute, the University of Pretoria, and the National Science Foundation, USA (IOS-1122228).http://www.springer.com/life+sci/biochemistry/journal/360hb2013ab201

Torpor in dark times : patterns of heterothermy are associated with the lunar cycle in a nocturnal bird

Many studies have shown that endotherms become more heterothermic when the costs of thermoregulation are high and /or when limited energy availability constrains thermoregulatory capacity. However, the roles of many ecological variables, including constraints on foraging opportunities and/ or success, remain largely unknown. To test the prediction that thermoregulatory patterns should be related to foraging opportunities in a heterothermic endotherm, we examined the relationship between the lunar cycle and heterothermy in Freckled Nightjars (Caprimulgus tristigma), which are visually orienting, nocturnal insectivores that are dependent on ambient light to forage. This model system provides an opportunity to assess whether variation in foraging opportunities influences the expression of heterothermy. The nightjars were active and foraged for insects when moonlight was available but become inactive and heterothermic in the absence of moonlight. Lunar illumination was a much stronger predictor of the magnitude of heterothermic responses than was air temperature (Ta). Our data suggest that heterothermy was strongly related to variation in foraging opportunities associated with the lunar cycle, even though food abundance appeared to remain relatively high throughout the study period. Patterns of thermoregulation in this population of Freckled Nightjars provide novel insights into the environmental and ecological determinants of heterothermy, with the lunar cycle, and not Ta, being the strongest predictor of torpor use.The University of Pretoria; the Natural Sciences and Engineering Research Council, Canada; and the DST/NRF Centre of Excellence at the Percy FitzPatrick Institute.http://www.uk.sagepub.com/journals/Journal200933ab201

Comparative techno-economic and life cycle analyses of synthetic “drop-in” fuel production from UK wet biomass

Renewable synthetic hydrocarbon “drop-in” fuels can help mitigate greenhouse gas emissions from transport, particularly in hard-to-abate sectors like freight and aviation. However, no study has extensively addressed the concerns over biomass availability, cost viability, and CO2 reduction feasibility that are associated with diverse production configurations and feedstocks. Here, we report detailed techno-economics and life cycle greenhouse gas emission assessments of drop-in fuel productions via hydrothermal liquefaction to assess their economic viabilities, CO2 mitigation potentials, and prospects for scale-up specifically within the UK context. Our approach integrates key production factors which include regional availability of main feedstocks (digestates, food waste, biodegradable municipal waste, and sewage sludge), plant configurations (centralised vs decentralised) and hydrogen sources (grey, blue, green). We demonstrated the economic trade-off between economy-of-scale and feedstock transport distances in the centralised/decentralised configurations, and also the economic and emissions trade-offs associated with the use of different hydrogen sources. We find that co-processing of different waste feedstocks is an important strategy to minimise fuel selling price by enabling better economy of scale and feedstock transport, resulting in a fuel selling price of £14.76 – 20.30 per GJ. The corresponding greenhouse gas emissions from the co-processing case vary from 11.4 to 24.9 kg CO2eq per GJ for 2021, based on the consequential life cycle assessment approach. Furthermore, we estimated that the utilisation of key UK wet feedstocks could only provide 4.5 % of current fuel consumptions and reduce emissions by 4.5 – 5.4 Mt CO2eq/year, which translates to 3.4 – 4.0 % reduction in the UK’s 2021 transport emissions

A review of techno-economic analyses and life cycle greenhouse gas emissions of biomass-to-hydrocarbon “drop-in” fuels

Synthetic “drop-in” fuels are compatible with existing fuel and vehicle infrastructures and, when produced sustainably, they could play an important role in mitigating the emissions of greenhouse gases (GHG) from transportation, especially in the hard-to-decarbonise sectors like freight and aviation. However, there is a need to understand the availability of biomass resources for drop-in fuel applications and the potential challenges associated with using these feedstocks including the supply chain issues. Hence, this paper offers a critical review of non-food biomass and drop-in fuel production including the biomass availability in the UK, the production of drop-in fuels from biomass feedstocks via thermochemical routes, estimated fuel production prices and volumes, and life cycle GHG impacts. The paper explores several fuel production factors, including energy and hydrogen requirements, as well as supply-chain considerations, which were used to estimate the drop-in fuel potential in the UK economy. We estimate the availability of non-food biomass resources in the UK to be in the range of 167–205 Mtpa (wet) [839–1033 PJ per year], as more than 50 % of these volumes are from high moisture content feedstocks such as biogenic municipal waste and sewage sludge. Other biomass feedstocks that are produced in significant quantities include straw and wood waste. Also, it is estimated that the total UK drop-in fuel manufacturing potential is in the range of 269–563 PJ per year. When used to displace fossil fuels in road transportation, this could lead to a total GHG reduction of 18.7–64.4 Mt. CO2eq per year which is 18.8–64.7 % relative to the UK's overall road transport emissions from all fuels in 2021

The impact of humidity on evaporative cooling in small desert birds exposed to high air temperatures

Environmental temperatures that exceed body temperature (Tb) force endothermic animals to rely solely on evaporative cooling to dissipate heat. However, evaporative heat dissipation can be drastically reduced by environmental humidity, imposing a thermoregulatory challenge. The goal of this study was to investigate the effects of humidity on the thermoregulation of desert birds and to compare the sensitivity of cutaneous and respiratory evaporation to reduced vapor density gradients. Rates of evaporative water loss, metabolic rate, and Tb were measured in birds exposed to humidities ranging from ∼2 to 30 g H2O m23 (0%–100% relative humidity at 307C) at air temperatures between 447 and 567C. In sociable weavers, a species that dissipates heat primarily through panting, rates of evaporative water loss were inhibited by as much as 36% by high humidity at 487C, and these birds showed a high degree of hyperthermia. At lower temperatures (407–447C), evaporative water loss was largely unaffected by humidity in this species. In Namaqua doves, which primarily use cutaneous evaporation, increasing humidity reduced rates of evaporative water loss, but overall rates of water loss were lower than those observed in sociable weavers. Our data suggest that cutaneous evaporation is more efficient than panting, requiring less water to maintain Tb at a given temperature, but panting appears less sensitive to humidity over the air temperature range investigated here.DST/National Research Foundation Centre of Excellencehttp://www.journals.uchicago.edutoc/pbz/tm201