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Hot Birds - Climate change and desert birds

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2019 was the 10th anniversary of the ‘Hot Birds Research Project’ (HBRP), a programme that integrates behavioural and physiological approaches to predict the impact of climate change on arid-zone birds in southern Africa and globally. The HBRP’s research focuses mainly on birds in arid habitats in southern Africa, but also involves work in North America and Australia, and increasingly extends to habitats other than deserts.

In July 2019, the Hot Birds Research project team held a very successful workshop at Gobabeb Research and Training Centre in the Namib Desert to celebrate 10 years of hot birds research (Photo: Nick Pattinson)

Ten years of the Hot Birds Research Project

The HBRP came into being in mid-2009, when the late Prof. Phil Hockey and Andrew McKechnie spent two days brainstorming a new research programme on land birds and climate change. From humble beginnings consisting of three researchers at Tswalu Kalahari Reserve during the summer of 2009/10, the HBRP has grown into a team of about 20 researchers spanning three South African universities, SANBI and a number of overseas institutions. In its first decade, some 75 papers have emanated from HBRP research, and 35 MSc and PhD students have been trained, most of them funded by the Fitz Centre of Excellence. To celebrate the HBRP’s 10th anniversary in 2019, the team held a three-day workshop at Gobabeb Research and Training Centre in the Namib Desert, where we took stock of current HBRP projects and the major questions that will drive our research for the next 10 years. One of the highlights was being joined at Gobabeb by Prof. Michael Kearney from U. Melbourne. Michael is an authority on modelling thermal landscapes and energy and water fluxes that occur between birds and their surroundings and has led the development of novel modelling approaches that hold great promise for predicting the vulnerability of birds to higher temperatures, highlighting critical knowledge gaps and allowing us to better target our field studies. Michael’s time at Gobabeb allowed us to integrate biophysical models into several current hot birds projects.

Another important advance has been the development, led by Amanda Bourne and Celiwe Ngamphalala, of non-invasive techniques for measuring stress physiology and energy and water balance in free-ranging birds. Using study populations of habituated birds, we can now measure behavioural and physiological responses to high temperatures simultaneously. These techniques will allow us to ground-truth laboratory physiology measurements against comparable measures in free-living birds, letting us assess the impacts of captivity stress on these measures and improve our predictions of how species respond to high temperatures under natural conditions.

A number of continuing HBRP studies examine links between temperature, behaviour and fitness in desert birds and focus on how increasingly frequent periods of hot weather negatively affect the ability of adult birds to maintain body condition, as well as their capacity to breed successfully. These effects of rising temperatures drive declines in both adult survival and breeding success and have the potential to drive major declines in populations as their habitats become hotter. While less dramatic than large-scale mortality events, such as birds dropping dead from heat during the devastating Australian heat wave of December 2019, these sublethal consequences of chronic exposure to sustained hot weather are emerging as the major threat to southern Africa’s desert avifauna. A risk assessment conducted by Shannon Conradie as part of her MSc and published in the Proceedings of the National Academy of Sciences of the U.S.A. in 2019 revealed that, in the absence of meaningful reductions in carbon emissions, the Kalahari of the late 21st Century will be too hot for our long-term study species: Southern Pied Babblers Turdoides bicolor, Southern Fiscals Lanius collaris, Southern Yellow-billed Hornbills Tockus leucomelas.

Heat dissipation behaviour – a global perspective

One of the longest-standing hot birds projects, which has been ongoing since 2009, focuses on whether readily-observable heat dissipation behaviours such as panting and wing-spreading can provide a quantitative index of species’ vulnerability to rising temperatures. In addition to a large data set for Kalahari species, we have collected comparable data for bird communities in the Sonoran Desert of North America and the Gascoyne region of western Australia. During 2019, Nick Pattinson and a team of collaborators completed a global analysis on avian heat dissipation behaviour, and a manuscript based on this work was accepted by Journal of Avian Biology in December 2019. The late Phil Hockey is senior author on this paper, as he was the first to suggest that behavioural data requiring little more than binoculars and a thermometer to collect may provide an easily quantifiable metric of susceptibility to negative effects of high temperatures on arid-zone birds.

Heat dissipation and foraging behaviour in Tankwa Karoo larks and chats

In 2019, the HBRP made its first foray into South Africa’s most extreme desert: the Tankwa Karoo. CB MSc student Matthew Orolowitz spent October and November in the Tankwa, collecting data on the behavioural responses of the region’s lark and chat species to high temperatures, and measuring the thermal landscape using black globe thermometers. Matthew investigated whether thermoregulatory behaviour could predict the strength of foraging trade-offs in the heat. He found that, among larks, drinking behaviour (i.e. whether birds made use of surface water sources or obtained their water from food) was the strongest predictor of the temperature at which birds retreated to shaded microsites and began panting. However, the reduction in foraging effort as temperatures increased was better correlated with body size (not drinking behaviour), suggesting that the apparent foraging-thermoregulation trade-off might not be mediated by shade-seeking and panting behaviours in these birds. Matthew is writing up his dissertation and will submit his results for publication in 2020.

Red Larks – combining behaviour, physiology and modelling

PhD student Ryno Kemp completed his final year of data collection on the Vulnerable Red Lark Calendulauda burra. He focused on sublethal fitness costs during hot weather and how these differ between sexes. In addition, body mass data for habituated individuals weighing themselves every morning and afternoon have revealed important differences between males and females in terms of how daily maximum air temperatures affect body condition. These data provide the basis for modelling how warming temperatures will affect the species in coming decades. The picture that has emerged from this project is concerning, as male Red Larks will experience large increases in risks of chronic negative effects of hot weather. Ryno is also working on the home range data he collected to estimate the population size for Black Mountain Mine conservation area as well as a manuscript combining all the data to model the water and energy budget for Red Larks under current and future climatic scenarios.

Climate change impacts on breeding success

Nick Pattinson and Ben Murphy began their PhDs in 2018 on Southern Yellow-billed Hornbills and Fork-tailed Drongos Dicrurus adsimillis at the Kuruman River Reserve in the Northern Cape. Both species are resident in the Kalahari Desert, and attempt to breed in spring and summer when resource abundance peaks. However, high resource availability coincides with high air temperatures, meaning that both species must handle severe heat stress during their breeding attempts. Previous studies on these species have shown effects of rainfall and heat stress on their ecology in the Kalahari. For the hornbills, 10 years of monitoring at this study site has revealed how increasing temperatures and decreasing rainfall drastically reduce breeding performance. Nick is using an experimental approach to disentangle the effects of temperature and resource availability to elucidate what is driving variation in hornbill reproductive performance. He is measuring physiological and behavioural responses to heat stress and variation in resource availability.

Ben is looking more specifically at behavioural responses to heat stress, and how they relate to breeding performance. Ben’s work follows earlier research by the HBRP team suggesting that Fork-tailed Drongos may be a “Darwinian demon” –they seem to show no negative effects of heat-stress-driven reductions in provisioning on pre-fledgling condition or fledging probability. Ben uses an experimental and observational approach to investigate whether drongos buffer fledgling mass during the nestling cycle by altering foraging and provisioning strategies at high air temperatures. Additionally, Ben is examining whether drongos might mitigate offspring thermoregulatory costs through nest shading and is also exploring whether underlying physiological capacity to regulate body temperature during activity at high air temperature further defines parental behavioural strategies.

Krista Oswald submitted her PhD at Rhodes University on Cape Rockjumpers Chaetops frenatus in the Fynbos mountains. She concluded that Rockjumper populations are likely to see strong negative impacts from climate change, predominantly through reduced reproductive success. Rockjumper nests had greater chance of succeeding at low temperatures due to reduced snake activity, although nests in recently burned habitat also had higher success. Krista also found Rockjumpers have low overall genetic diversity, and so may show limited adaptive capacity to rapid environmental changes. Krista published one paper in Animal Behaviour in 2019, and she is back in Canada preparing more manuscripts from her PhD.

Can sociality buffer climate change impacts?

PhD student Amanda Bourne has been studying the ways in which cooperative social behaviour might buffer the fitness costs and consequences of exposure to high temperatures and drought, using Southern Pied Babblers as a model species. Pied Babblers are cooperative breeders with natural variation in group size, and are endemic to the hot and dry Kalahari. In 2019, Amanda completed her lab and field work and wrote the bulk of her thesis. She found that both successful reproduction and the probability of interannual survival are severely compromised during hot and dry weather, suggesting that this species may face population persistence challenges as climate change advances, bringing with it more frequent and hotter heat waves and droughts. Although Pied Babbler groups with more helpers often produce more surviving young overall, larger group sizes do not appear to moderate the effects of high temperatures and drought, suggesting that these conditions act on individuals via physiological tolerance limits and resource constraints. Amanda uses a combination of behavioural observations and non-invasive measurements of energy expenditure and water turnover to build a holistic picture of the mechanisms linking high temperatures and drought to fitness costs in these birds. One of her chapters was published in 2019, in Functional Ecology, and a further two chapters are currently under review, at Ecology Letters and Proceedings of the Royal Society B, respectively

Non-invasive techniques

Handling stress may obscure the very signatures of environmental stress that the HBRP team is interested in, so finding less invasive ways to measure physiology in wild birds is an important research priority. The HBRP team have been developing and testing non-invasive methods for measuring physiological responses and this has resulted in publications in Functional Ecology and General and Comparative Endocrinology. Some of this research, led by Amanda Bourne, focuses on measuring metabolic rates and water turnover using a novel doubly-labelled water technique involving oral dosing and faecal sampling instead of the more traditional injecting and blood sampling. A proof of concept study has demonstrated that faeces provided an adequate substitute for blood as a source of body water, and both non-invasive dosing and non-invasive sampling proved feasible in the field.

Another part of this research, led by PhD student Celiwe Ngcamphalala, focuses on quantifying in glucocorticoid (“stress hormone”) concentrations. This involves the validation of appropriate enzyme immunoassays (EIA) to quantify faecal glucocorticoid metabolites (fGCM) in four species. The use of fGCM analysis allows for non-invasive sampling by removing both the need to bleed birds and the need to catch or handle the birds to quantify stress responses, i.e. samples can be collected from free-ranging individuals.  Using the assays validated by former HBRP Honours student Emma Jepsen, Celiwe and BTech student Lesedi Moagi have shown that stress responses to maximum daily temperatures vary between captive and free-ranging Southern Pied Babblers, which reinforces the importance of these non-invasive sampling techniques that can be applied in the birds’ natural environment. without imposing capture or handling stress.

Variation in evaporative cooling capacity

Habitats vary widely in terms of the physiological challenges they pose to animals, and much remains to be learned about how the thermal physiology of birds has evolved in response to different sets of environmental variables. Current literature regarding avian thermoregulation in the heat is dominated by studies on species inhabiting hot, arid regions. As a result, our understanding of whether species residing in non-arid habitats are less, equally or possibly even more physiologically vulnerable to potential future increases in air temperature, remains limited. PhD student Marc Freeman aims to improve our understanding in this area through quantifying variation in avian evaporative cooling efficiency, heat tolerance and assessing the effect of increasing humidity in phylogenetically diverse avian taxa. The project will be conducted for multiple species within three climatically-contrasting biome types (desert, montane grassland, thicket and subtropical forests) representing a gradient of maximum air temperatures. One key variable Marc’s research will focus on is humidity: even though maximumair temperatures in coastal forests are lower than those in deserts, high humidity is likely to severely curtail the capacity of birds to dissipate heat by evaporation. By the end of 2019 Marc had collected data from ~20 species inhabiting grasslands in the eastern Free State province, and January 2020 saw him continuing this work in the Richard’s Bay area.

Climate change past, present and future

In 2019. Shannon Conradie registered for a PhD which expands on the findings of her MSc. Her work focuses on developing novel modelling approaches integrating the thermal landscape, heat and water fluxes and behavioural decisions and trade-offs for desert birds currently and under future climate change scenarios. Ultimately, her study will enable us to construct detailed models of survival and reproduction in birds, reducing the need for detailed species-specific empirical datasets to predict avian responses to climate change., Shannon spent time in the USA developing skills in biophysical modelling approaches and dynamic state variable models. Currently Shannon is working on refining these modelling techniques and validating model outputs with empirical data collected from the Kalahari Desert in Southern Africa.


  • Our biannual workshop was held at Gobabeb in the Namib Desert to commemorate the 10th Anniversary of the HBRP. We were joined by collaborators Profs Michael Kearney and Blair Wolf, both of whom provided valuable input.
  • A paper by Shannon Conradie and co-authors titled “Chronic, sublethal effects of high temperatures will cause severe declines in southern African arid-zone birds during the 21st century” was published in the prestigious journal Proceedings of the National Academy of Sciences of the USA.
  • The HBRP published another 15 papers in international peer-reviewed journals in 2019.
  • Susie Cunningham, Amanda Bourne, Nicholas Pattinson, Celiwe Ngcamphalala, Barry van Jaarsveld and Andrew McKechnie presented papers at the Australasian Ornithological Conference held in Darwin, Australia in July.
  • Shannon Conradie and Mpho Malematja graduated with MSc degrees from the University of Pretoria.
  • HBRP research was featured in a Carte Blanche insert on the effects of climate change on animals in the Kalahari; and in a radio interview with Radio Sonder Grense.
  • HBRP collaborator Janet Gardner of the Australian National University in Canberra received a grant that includes funds for exchange visits by Amanda Bourne and Janet’s PhD student, Lynda Sharpe.

Key co-supporters
DST-NRF CoE grant; SARChi Chair in Conservation Physiology, UCT URC, U. Pretoria; NRF Thuthuka Grant; NRF CSUR Grant, Tygerberg Bird Club.

Research Team
Prof. Andrew McKechnie (U. Pretoria / SANBI)
Dr Susie Cunningham (FIAO, UCT)
Dr Janet Gardner (Australian National University)
Dr Alex Gerson (U. Massachusetts)
Dr Alan Lee (FIAO, UCT / SANBI)
Dr Rowan Martin (FIAO, UCT)
Dr Todd McWhorter (U. Adelaide)
Dr Ben Smit (Rhodes)
Dr Zenon Czenze (U. Pretoria)
Dr Blair Wolf (U. New Mexico)
A/Prof. Amanda Ridley (U. Western Australia)
Dr Tom Flower (FIAO, UCT / Capilano University)

Students: Amanda Bourne (PhD, UCT); Shannon Conradie (PhD, Pretoria); Marc Freeman (PhD, Pretoria); Ryno Kemp (PhD, Pretoria); Benjamin Murphy (PhD, UCT); Celiwe Ngcamphalala (PhD, Pretoria); Matthew Noakes (PhD, Pretoria); Krista Oswald (PhD, Rhodes); Nicholas Pattinson (PhD, UCT); Michelle Thompson (PhD, Pretoria); Miqkayla Stofberg (MSc, UCT); Barry van Jaarsveld (MSc, Pretoria); Matthew Orolowitz (CB MSc, UCT); Lesedi Moagi (BTech, TUT); Andries Janse van Vuuren (Hons, Pretoria); Michelle Bouwer (Hons, Pretoria).

Research Assistants:  Lauren Bailey, Jo Balmer, Shelby Bohn, Cameron Brock, Rachel Bucksey, Josephine Bruning, John Diener, Lizzie Diener, Carla Dodd, Gabe Foley, Samantha Fourie, Amy Hunter, Justin Jacobs, Rowan Jordaan, Craig Kenny, Danielle Keys, Noxolo Kinzela, Vuyiseka Mbiko, Sakhile Mkhize, Lesedi Moagi, Sophie Monsarrat, Angela Moreras, Ceili Peng, Anna Probert, Keegan Schoeman, Alyssa Stulberg, Jack Thorley, Alex Thouxeau, Amy Tipton, Samantha Wagstaff.