Extreme hyperthermia tolerance in the world’s most abundant wild bird

Abstract

Accordingly, we predicted pronounced facultative hyperthermia buffers individual queleas from dehydration risk. To test this prediction, we quantified relationships between body temperature, evaporative heat loss and metabolic heat production in red-billed queleas in South Africa. Methods All experimental procedures were approved by the University of Pretoria's Animal Ethics Committee (NAS181/2019) and the Research Ethics and Scientific Committee of the South African National Biodiversity Institute (SANBI NZG/RES/P19/13) and birds were captured under permit JM 8,057/2019 from the Free State province's Department of Economic, Small Business Development, Tourism and Environmental Affairs. The methods we used for quantifying the upper limits of evaporative cooling capacity and heat tolerance followed those of a recent series of studies of avian heat tolerance 27-30. Study site and species. We trapped 20 red-billed queleas (body mass = 17.94 ± SD 1.19 g) using mist nets in agricultural fields near the town of Harrismith in South Africa (28° 06′ S, 29°10′E, 1754 m asl) during November 2019 (early austral summer). After capture, birds were transported by road (approximately 20-min trip) in cloth bags to a field laboratory, where they were held in cages (600 × 400 × 400 mm) for 1-16 h with ad libitum access to water and wild bird seed. Food was removed at least one hour prior to gas exchange and body temperature measurements, allowing individuals to habituate and ensure they were post-absorptive 31. Air and body temperature measurements. Body temperature was measured using a temperaturesensitive passive integrated transponder (PIT) tag (Biotherm 13, Biomark, Boise, ID, USA) injected intraperitoneally in each bird. Prior to injection, all PIT tags were calibrated in a circulating water bath (model F34, Julabo, Seelbach BW, DE) over temperatures ranging 35 to 50 °C against a thermocouple meter (TC-1000, Sable Systems, Las Vegas, NV, USA), the output of which was verified against a mercury-in-glass thermometer with NIST-traceable accuracy before and after the PIT tag calibration. Temperatures measured by PIT tags deviated by 0.28 ± 0.23 °C (n = 23) from actual values and we corrected all measured values accordingly. Data from the PIT tags were recorded using a reader and transceiver system (HPR + , Biomark, Boise ID, USA). To measure air temperature during the gas exchange measurements, we inserted a thermistor probe (TC-100, Sable Systems, Las Vegas, NV, USA) through a hole sealed with a rubber grommet in the side of each metabolic chamber.

Phenotypic flexibility in heat production and heat loss in response to thermal and hydric acclimation in the zebra finch, a small arid-zone passerine

“…Overall, regulation of body temperature in zebra finches below their T LC was not affected by acclimation regimes. At T a > 36 °C, T b increased linearly together with linear increase of evaporative heat loss and the efficiency of evaporative heat loss (EHL/MR), as in other Australian and Southern African passerines of similar m b (Freeman et al 2020;McKechnie et al 2017;Whitfield et al 2015). Conversely, Cooper et al (2020b) found that acclimation of zebra finches to experimental conditions mimicking heatwave did not increase their T b as it was recorded under natural conditions (Cooper et al 2020a).…”

How hornbills handle heat: sex-specific thermoregulation in the southern yellow-billed hornbill

“…Tolerance of unusually high T b in a central American passerine has been suggested to be functionally linked to impeded EHL in humid environments (Weathers, 1981), the reasoning on which our prediction of more pronounced facultative hyperthermia in female hornbills was based. The observation of Weathers (1981), as well as those of a handful of other authors reporting avian tolerance of T b >45°C (Arad and Marder, 1982;Dmi'el and Tel-Tzur, 1985;Freeman et al, 2020), reiterates the need to determine the upper limits to hyperthermia tolerance in many more species, and to evaluate the relative roles of deleterious temperature effects on cell membrane fluidity, transport pathways across membranes and other aspects of macromolecule function (Adolph, 1947;Roti Roti, 2008) and oxygen supply limitation (Teague et al, 2017;Pörtner et al, 2017) in determining these limits.…”

The Effects of Weather on Avian Growth and Implications for Adaptation to Climate Change

“…Consequently, small nestlings may be more susceptible to high temperatures in water-limited environments than large nestlings because of potential dehydration (Whitfield et al, 2015). However, many small birds that live in hot and arid environments will have adaptive strategies, like facultative hyperthermia, that allow tolerance of challenging high temperatures (Gerson et al, 2019;Freeman et al, 2020).…”