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

The ecology and evolution of mammalian heterothermy in a changing world

No abstract available.http://onlinelibrary.wiley.com/journal/10.1111/(ISSN)1469-79982015-02-28hb201

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

Heterothermy in Afrotropical mammals and birds : a review

Recent years have seen a rapid increase in the number of Afrotropical endotherms known to avoid mismatches between energy supply and demand by using daily torpor and/or hibernation. Among mammals, heterothermy has been reported in 40 species in six orders, namely Macroscelidea, Afrosoricida, Rodentia, Eulipotyphla, Primates and Chiroptera. These species span a range in body mass of 7–770 g, with minimum heterothermic body temperatures ranging from 1–278C and bout length varying from 1 h to 70 days. Daily torpor is the most common form of heterothermy, with true hibernation being observed in only seven species, Graphiurus murinus, Graphiurus ocularis, Atelerix frontalis, Cheirogaleus medius, Cheirogaleus major, Microcebus murinus and Microcebus griseorufus. The traditional distinction between daily torpor and hibernation is blurred in some species, with free-ranging individuals exhibiting bouts of 424 h and body temperatures 5168C, but none of the classical behaviours associated with hibernation. Several species bask in the sun during rewarming. Among birds, heterothermy has been reported in 16 species in seven orders, and is more pronounced in phylogenetically older taxa. Both in mammals and birds, patterns of heterothermy can vary dramatically among species occurring at a particular site, and even among individuals of a single species. For instance, patterns of heterothermy among cheirogalid primates in western Madagascar vary from daily torpor to uninterrupted hibernation for up to seven months. Other examples of variation among closely-related species involve small owls, elephant shrews and vespertilionid bats. There may also be variation in terms of the ecological correlates of torpor within a species, as is the case in the Freckled Nightjar Caprimulgus tristigma.The Mammal Research Institute, University of Pretoriahttp://icb.oxfordjournals.org/ab201

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

Interspecific variation in thermoregulation among three sympatric bats inhabiting a hot, semi-arid environment

Bats in hot roosts experience some of the most thermally challenging environments of any endotherms, but little is known about how heat tolerance and evaporative cooling capacity varies among species. We investigated thermoregulation in three sympatric species (Nycteris thebaica, Taphozous mauritianus, and Sauromys petrophilus) in a hot, semi-arid environment by measuring body temperature (Tb), metabolic rate and evaporative water loss (EWL) at air temperatures (Ta) of 10 - 42 °C. S. petrophilus was highly heterothermic with no clear thermoneutral zone, and exhibited rapid increases in EWL at high Ta to a maximum of 23.7 ± 7.4 mg g-1 hr-1 at Ta ≈ 42 °C, with a concomitant maximum Tb of 43.7±1.0 °C. T. mauritianus remained largely normothermic at Tas below thermoneutrality, and increased EWL to 14.7 ± 1.3 mg g-1 hr-1 at Ta ≈ 42 °C, with a maximum Tb of 42.9 ± 1.6 °C. In N. thebaica, EWL began increasing at lower Ta than in either of the other species, and reached a maximum of 18.6±2.1 mg g-1 hr-1 at Ta = 39.4 °C, with comparatively high maximum Tb values of 45.0±0.9°C. Under the conditions of our study, N. thebaica was considerably less heat tolerant than the other two species. Among seven species of bats for which data on Tb as well as roost temperatures in comparison to outside Ta are available, we found limited evidence for a correlation between overall heat tolerance and the extent to which roosts are buffered from high Ta.This study was facilitated by funding from Bat Conservation International, the National Research Foundation and the University of Pretoria.http://www.springer.com/life+sci/biochemistry/journal/360hb2013ab201

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