Global variation in avian metabolic rates and the slow pace of life of tropical birds

No abstract available.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1365-24352016-03-31hb201

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

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

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

Thermal physiology of a range-restricted desert lark

Please read abstract in the article.Supplementary material 1: Typical red lark (Calendulauda burra) habitat at our study site at Black Mountain Conservation Area, Aggeneys, South Africa.Supplementary material 2: Red lark (Calendulauda burra) resting in a shaded microsite on a very hot day at Black Mountain Conservation Area, Aggeneys, South Africa. The air temperature at the time the video was recorded was 39 °C. (MP4 31812 KB) (https://link.springer.com/article/10.1007/s00360-018-1190-1#Sec18)http://link.springer.com/journal/360hj2020Zoology and Entomolog

The physiology of heat tolerance in small endotherms

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.The National Research Foundation of South Africa and the National Science Foundation.http://www.physiologyonline.org2020-09-01hj2020Zoology and Entomolog

Experimental sources of variation in avian energetics : estimated basal metabolic rate decreases with successive measurements

Basal metabolic rate (BMR) is one of the most widely used metabolic variables in endotherm ecological and evolutionary physiology. Surprisingly few studies have investigated howBMR is influenced by experimental and analytical variables over and above the standardized conditions required for minimum normothermic resting metabolism. We tested whether avian BMR is affected by habituation to the conditions experienced during laboratory gas exchange measurements by measuring BMR five times in succession in budgerigars (Melopsittacus undulatus) housed under constant temperature and photoperiod. Both the magnitude and the variability of BMR decreased significantly with repeated measurements, from 0.410 0.092 W (n p 9) during the first measurement to 0.285 0.042 W (n p 9) during the fifth measurement. Thus, estimated BMR decreased by ∼30% within individuals solely on account of the number of times they had previously experienced the experimental conditions. The most likely explanation for these results is an attenuation with repeated exposure of the acute stress response induced by birds being handled and placed in respirometry chambers. Our data suggest that habituation to experimental conditions is potentially an important determinant of observed BMR, and this source of variation needs to be taken into account in future studies of metabolic variation among individuals, populations, and species.University of Pretoriahttp://www.journals.uchicago.edu/toc/pbz/current2015-09-30hb201

Partitioning of Evaporative Water Loss into Respiratory and Cutaneous Pathways in Wahlberg's Epauletted Fruit Bats ( Epomophorus wahlbergi

Please read abstract in the article.National Research Foundation.http://www.journals.uchicago.edutoc/pbz/currenthb201

A prenatal acoustic signal of heat afects thermoregulation capacities at adulthood in an arid‑adapted bird

Understanding animal physiological adaptations for tolerating heat, and the causes of interindividual variation, is key for predicting climate change impacts on biodiversity. Recently, a novel mechanism for transgenerational heat adaptation was identified in a desert-adapted bird, where parents acoustically signal hot conditions to embryos. Prenatal exposure to “heat-calls” adaptively alters zebra finch development and their thermal preferences in adulthood, suggesting a long-term shift towards a heat-adapted phenotype. However, whether such acoustic experience improves long-term thermoregulatory capacities is unknown. We measured metabolic rate (MR), evaporative water loss (EWL) and body temperature in adults exposed to a stepped profile of progressively higher air temperatures (Ta) between 27 and 44 °C. Remarkably, prenatal acoustic experience affected heat tolerance at adulthood, with heat-call exposed individuals more likely to reach the highest Ta in morning trials. This was despite MR and EWL reaching higher levels at the highest Ta in heat-call individuals, partly driven by a stronger metabolic effect of moderate activity. At lower Ta, however, heat-call exposed individuals had greater relative water economy, as expected. They also better recovered mass lost during morning trials. We therefore provide the first evidence that prenatal acoustic signals have long-term consequences for heat tolerance and physiological adaptation to heat.The Australian Research Council, the Holsworth Wildlife Research Endowment and international travel costs by the National Research Foundation of South Africa.https://www.nature.com/srepdm2022Zoology and Entomolog