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The ‘Hot Birds Research Project’ (HBRP) is a research programme that integrates behavioural and physiological approaches to predict the impact of climate change on birds in southern Africa and globally. The HBRP’s research has historically focused 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.

On the 9th January 2024, the European Union’s Copernicus Climate Commission announced that 2023 was the hottest year since records began. Temperatures were close to 1.5°C above pre-industrial averages. This correlated with a return to El Niño conditions after several La Niña years. The record temperatures in 2023 coincided with record extreme events: including the lowest minimum winter sea ice ever recorded around Antarctica, massive destructive wildfires in Canada, southern Europe and Hawaii, and devastating floods in Libya. Climate change is no longer a threat looming in the future: the impacts are here and now. In response, the HBRP is increasingly working on red-listed species that already face other threats in addition to climate change. In addition, we are stepping up research on mitigation interventions and mechanistic modelling, and continuing data collection on how behaviour and physiology inform climate change vulnerability and resilience of birds.

Temperature effects on behaviour – habitat, hydration and humidity
During 2023, MSc student Jaimie Whyte submitted her thesis on the impacts of temperature on behavioural thermoregulation, microsite use, and foraging behaviour in White-browed Sparrow-Weavers Plocepasser mahali. Jaimie investigated whether habitat features had the potential to mitigate impacts of hot weather on the birds. She discovered that sparrow-weavers inhabiting shadier home ranges panted less at high air temperatures than those in sunnier home ranges, and as a consequence had higher foraging efficiency. She also showed that the shadiest home ranges significantly buffered evaporative water loss rates calculated for the birds, and that habitat structure may therefore be extremely important for persistence of this and other species under ongoing climate warming.

Meanwhile, MSc student James Short completed his fieldwork on the behaviour and physiology of chats and larks in the Tankwa Karoo desert. James assessed behavioural thermoregulatory responses of Karoo Chats Emarginata schlegelii to extremes of heat and cold in summer and winter and investigated whether these behavioural adjustments correlated with changes in foraging. James’ next steps are to map these results to long-term climate trends for the region to assess the potential effects of warmer winters and hotter summers for chat behaviour and foraging success. James’ second chapter compares physiological heat tolerances of Large-billed Larks Galerida magnirostris from the Tankwa Karoo to those of other bird species in arid environments; and assesses the impact of drinking behaviour on thermal physiology in small birds.

During 2023, PhD student Ben Murphy also investigated the importance of water to bird behaviour under hot conditions. He completed fieldwork for a study of the relationship between hydration status and behavioural responses of Fork-tailed Drongos Dicrurus adsimilis to high air temperatures. Ben altered the hydration status of drongos by feeding them either mealworms injected with extra water, or the same quantity of dry mealworms. He hypothesized that drongos fed water-enriched mealworms would have a greater capacity for evaporative cooling, and therefore might subsequently be able to maintain higher levels of foraging activity than those fed dry worms. Instead, Ben’s results showed that drongos fed water-enriched mealworms reduced foraging activity to a greater extent at high air temperatures than those fed dry mealworms. This surprising result suggests that water, rather than energy, is limiting for drongos when it is hot, such that birds will continue to forage during the heat in order to increase their water intake, but not their caloric intake. Ben continued to make good progress towards the completion of his PhD.

CB MSc student (2022/23 cohort) Bruce Chrispo, co-supervised by Ben and by Susie Cunningham and Chima Nwaogu, successfully completed his thesis on the impacts of temperature on nest success in the drongos and graduated in December 2023.

Also working in the Kalahari was CB MSc student Kim Daniels (2022/23 cohort). Kim completed her work on the potential for mistletoes Plicosepalus kalachariensis to provide thermal refuges for small birds in the southern Kalahari. She discovered that mistletoe clumps were cooler during the heat of the day and had a different humidity profile from their blackthorn Senegalia melifera host shrubs and from non-host blackthorns. Despite this, patterns of use of mistletoes and blackthorn by small birds (including Black-chested Prinias Prinia flavicans and Kalahari Scrub-robins Cercotricha paena) suggested that mistletoes were mostly targeted by birds as a foraging resource rather than a thermal refuge, at least under the conditions Kim encountered during her study period. Kim submitted her thesis in 2023 and graduated in December. She is currently working together with post-doc Mia Momberg to publish these results, together with a dataset collected by Mia on mistletoes in the Lowveld.

Continuing the theme of temperature effects on Kalahari bird behaviour, former PhD student Dr Amanda Bourne continued her incredible publishing record, with two further papers published during 2023 using data collected from the Southern Pied Babblers Turdoides bicolor at Kuruman River Reserve during her PhD. Amanda showed that helpers reduce helping behaviour more than parents during hot weather, explaining why group size does not seem to buffer adverse environmental conditions on breeding success in this species (published in Behavioral Ecology), and documented a new thermoregulatory behaviour in this species (published in Ostrich). 

The HBRP also conducted research on bird behaviour in mesic environments during 2023. MSc student Nazley Liddle submitted her thesis on interactions between temperature and humidity on thermoregulation and behaviour in Blue Waxbills Uraeginthus angolensis and other small mesic savanna bird species in humid northern KwaZulu-Natal. Nazley showed that Blue Waxbill thermal tolerance limits under humid conditions were lower than under dry conditions, and that they are therefore at greater risk under climate warming than previously predicted. Nazley also found complex, species-specific behavioural responses to increased heat and humidity among the mesic savanna bird community, with many species changing behaviour in response to both heat and humidity, but few common themes in the direction and strength of these responses.

Red-list species and mitigation interventions
The impacts of climate change are becoming ever clearer with extreme events including heatwaves, fire and flooding now a regular occurrence. There is no time left for a ‘wait and see’ approach to conservation in the face of climate change for already-threatened species. In 2023, the HBRP continued efforts to engage in research on red-listed species, and in development of conservation mitigation tools.

CB MSc student (2022/23 cohort) Michelle Bouwer submitted her thesis on the impacts of temperature and land-use change on hatching success in Blue Cranes Anthropoides paradiseus, graduating in December. She discovered that hatching success was negatively correlated with air temperature, and with increasing time parents left eggs unattended. This suggests both disturbance and climate change may impact future hatching success in the stronghold Overberg population.

CB MSc student (2023/24 cohort) Obakeng Pule continued work on the Southern Yellow-billed Hornbill Tockus leucomelas population at Kuruman River Reserve, previously studied by PhD students Tanja van de Ven and Nicholas Pattinson (2012–2021). Tanja and Nick found that hornbills are severely negatively affected by hot weather during breeding, with >50% of nests failing when average air temperatures during the nesting period exceeded 35°C. Tanja used path analysis to establish that 70% of the effect of air temperature on nest success occurred via direct effects of hot nestbox temperatures on nestling growth. Nick trialled a new insulated nestbox design during his PhD and found significantly weaker air temperature effects on nestling growth than Tanja had documented. However, the effect of the new nest box design used by Nick versus the old design used by Tanja, was confounded by the enormously variable weather conditions experienced in each study. Obakeng was funded by a WWF-USA Wildlife Adaptation Innovation Fund grant to experimentally assess the impact of box design itself, by monitoring nestling growth and nest outcomes in both uninsulated (old design) and insulated (new design) nestboxes in the 2022/23 and 2023/24 breeding seasons.

Obakeng’s preliminary results suggest that seasonal differences have large impacts on chick growth and nest outcomes over and above differences in box type. However, nests in insulated boxes are more likely to succeed than those in uninsulated boxes within the same season. Nestlings in insulated boxes also weigh more than those in uninsulated boxes, especially in the first few weeks of life. This is associated with buffering of negative temperature effects on very young nestlings (~1 week old) in insulated boxes. These promising preliminary results suggest nestbox insulation might be a cheap and effective way to improve breeding success under rising temperatures in nestbox-dependent species.

Carrie Hickman continued her PhD data collection on Southern Ground Hornbills Bucorvus leadbeateri in 2023, confirming that high temperatures cause these birds to display heat dissipation behaviour year-round (even in winter), and that their thermal thresholds for engagement in heat dissipation behaviour in winter are lower than in summer. In 2023, Carrie also collected data on operative environmental temperatures by placing black bulb thermometers in different microsites at midday in summer and winter (sun, shade, at different levels off the ground), and assessed the availability of these microsite types in each season. Using these data, she was able to show that environmental temperatures were higher in winter than in summer, for the same air temperature. This is because there is less shade available in the environment in winter, due to the large number of deciduous trees in this habitat. This may explain why ground hornbills pant at cooler air temperatures in winter than they do in summer.

Carrie also showed that winters are warming faster than summers in the lowveld, highlighting an unexpected avenue of vulnerability for birds in this region. Carrie is also working on impacts of temperature on maternal investment in eggs, and on nestling growth and physiology. At the time of writing, she is engaged in her final field season of data collection for these aspects of her study.

In 2023 we started a new project on the implications of warming temperatures for Secretarybirds Saggitarius serpentarius, led by PhD student Wesley Gush. Wesley will be studying effects of warm weather on parental care and nestling growth, fitting GPS trackers including accelerometers to fledglings to study impacts of weather on behaviour during the critical early years post-fledging, and assessing thermal tolerance in adult Secretarybirds using respirometry. In 2023, Wesley collected his first data from active Secretarybird nests in the Karoo nearby Calvinia. He placed trail cameras at nests and deployed trackers on five nestlings. At the time of writing, two of these have fledged and flown northwest towards Vryburg. Wesley has also begun training captive adult birds at Dullstroom Bird of Prey Centre to sit calmly in custom-designed respirometry chambers ahead of collecting thermal physiology data in 2024.

In a final highlight of 2023’s HBRP red-list species programme, Susie Cunningham and Peter Ryan were awarded a South African National Antarctic Programme grant from the NRF to start research on implications of climate change on the iconic surface nesting seabirds of Marion Island in 2024, including Northern and Southern Giant Petrels Macronectes halli and M. giganteus and Wandering Albatrosses Diomedea exulans.

Thermal physiology
A major theme for 2023 was understanding how the evaporative cooling capacity of forest birds is affected by humidity, reflecting the HBRP’s increasing expansion into mesic habitats. High atmospheric humidity severely limits the ability of animals to dissipate heat by evaporation, compared to under dry conditions, and exposes them to greater risk of body temperature exceeding lethal limits. For instance, humidity has been a major contributing factor to increasingly frequent heat-related mortality events among flying foxes in eastern Australia and is also thought to have exacerbated the conditions that led to South Africa’s first known die-off of wild birds in northern KwaZulu-Natal in November 2020. Several HBRP projects during 2023 focused on understanding how birds respond to a combination of high air temperature and elevated humidity, conditions becoming more frequent as climate change advances. One highlight of the year was the acceptance of a paper emanating from Marc Freeman’s PhD in the high-impact journal Ecology.

Bianca Coulson completed her MSc on thermoregulation in Trumpeter Hornbills Bycanistes bucinator. Working at St Lucia on the east coast, she measured Trumpeter Hornbills’ body temperature, evaporative water loss and metabolic heat production over a range of air temperatures and humidities matching those they experience naturally. At humidity representative of average summer conditions, the hornbills were easily able to regulate body temperature, even at air temperatures equivalent to the thermal conditions they experience at midday in the sun. However, when humidity approached the upper extremes of values recorded in the area over the last 20 years, the hornbills’ capacity to defend body temperature at safe levels virtually disappeared, leaving them unable to avoid severe lethal hyperthermia. Bianca’s data have also yielded the first estimate of maximum wet bulb temperature for a bird. This variable combines temperature and humidity into a single number and is widely used in analyses of human thermal safety. The maximum wet bulb temperature thought to be survivable by humans is 35C. The corresponding value for the hornbills, however, is 32C. Mapping the hornbills’ future exposure to this threshold value across their entire range reveals that several regions will become too hot and humid for the birds to persist by the end of the century.

Another highlight for 2023 involved Shannon Conradie and Andrew McKechnie contributing to a global analysis of risks posed by climate change to arid-zone birds published in Nature Communications. This study, which linked dehydration risk assessments with desert avian diversity patterns, identified areas in the world’s deserts that will act as thermal refugia in coming decades, and evaluated the extent to which current protected areas include these future refugia. At present, less than 20% are protected, but the analysis presented in this study will hopefully aid the identification of new protected areas in future.

Modelling climate change impacts
Predicting the impacts of rising temperatures and more frequent extreme weather events on birds and other animals requires a detailed understanding of how birds operate in the thermal landscapes they occupy, and how heat transfer between those landscapes and birds constrains their ability to survive and reproduce. In 2023 Shannon Conradie continued work developing methods to assess the amount of empirical behaviour data required to ensure model predictions of thermoregulatory costs are accurate under complex field conditions. Preliminary results suggest detailed focal data are needed for biophysical models to accurately predict daily energy expenditure in Southern Pied Babblers Turdoides bicolor under field conditions, but fewer data are needed if these are strategically sampled across days of different maximum daily air temperature. Shannon is also working on how to include drinking behaviour to ensure accurate modelling of water costs, using empirical data from White-browed Sparrow-weavers Plocepasser mahali, and working on assessing the capacity of biophysical modelling to predict breeding outcomes of bird populations based on remote sensing data of conditions in the field.

Shannon Conradie and Susie Cunningham co-supervised BSc Hons student, Martiné van den Berg. Martiné assessed whether detailed species-specific morphometrics could be substituted with more general measurements from model species in the parameterization of biophysical models. She found that models parameterized with plumage measurements from House Sparrows Passer domesticus were just as successful at predicting White-browed Sparrow-weaver body temperature and evaporative water loss under respirometry conditions as those parameterized with plumage measurements from the sparrow-weavers themselves, suggesting that it may be possible to use generalized measurements for some model parameters under the right conditions. Martiné was awarded a Distinction for her work.


  • The HBRP published 17 papers in international peer-reviewed journals in 2023, including Global Change Biology, Nature Communications, Ecology, Behavioral Ecology and more.
  • Susie Cunningham was promoted to Associate Professor and Director of the FitzPatrick Institute.
  • Ben Murphy won Best Presentation by a PhD student at the Learn About Birds Conference held in Wilderness in May.
  • CB MSc student Sean Morar graduated in March 2023 and CB MSc students Michelle Bouwer, Bruce Chrispo and Kim Daniels all graduated in December 2023.
  • MSc students Nazley Liddle, Jaimie Whyte and Bianca Coulsen all submitted their theses.
  • Martiné van den Berg, Bianca Coulsen and Jaimie Whyte were all awarded their degrees with Distinction (we still await Nazley Liddle’s results at the time of writing).
  • Wesley Gush began a new PhD studying climate change impacts on Secretarybirds.
  • Wesley Gush and Carrie Hickman were both successful in attracting Rufford Foundation funding for their projects on Secretarybirds and Southern Ground-hornbills, respectively.
  • Susie Cunningham and Peter Ryan were successful in attracting a SANAP grant for research on on-island impacts of climate change on albatrosses and giant petrels on sub-Antarctic Marion Island in 2024. 
  • Susie Cunningham was awarded a WWF-USA Wildlife Adaptation Innovation grant to assess impacts of providing insulated nest boxes on Southern Yellow-Billed Hornbill nest success.
  • Andrew McKechnie was elected to the Council of the Royal Society of South Africa.
  • Shannon Conradie was short-listed as one of the top three applicants for the prestigious Jennifer Ward Oppenheimer Research Grant. .

Key co-supporters
SARChi Chair in Conservation Physiology; UCT URC; U. Pretoria; NRF Thuthuka Grant; Francois van der Merwe; John Solomon; WWF USA; Rufford Foundation; VC Future Leaders Programme, UCT; Associated Private Nature Reserves.

Research team 2023
Prof. Andrew McKechnie (U. Pretoria / SANBI)
A/Prof. 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 Ben Smit (Rhodes)
Dr Zenon Czenze (U. New England)
Dr Blair Wolf (U. New Mexico)
A/Prof. Amanda Ridley (U. Western Australia)
Dr Tom Flower (FIAO, UCT / Capilano University)
Dr Izak Smit (SANParks)
Dr Stephanie Payne (U. Pretoria)
Dr Rita Covas (U. Porto, UCT)
Dr Shannon Conradie (UCT)
Dr Celiwe Ngcamphalala (UCT)
Dr Chima Nwaogu (UCT)
Dr Mia Momberg (U. Pretoria)
Dr Marc Freeman (U. Pretoria)
Dr Amanda Bourne (Australian Wildlife Conservancy)

Students: Carrie Hickman (PhD, UCT); Ryno Kemp (PhD, Pretoria); Wesley Gush (PhD, Pretoria); Benjamin Murphy (PhD, UCT); Nicholas Pattinson (PhD, UCT); Miqkayla Stofberg (PhD, UCT); Nazley Liddle (MSc, Pretoria); Otto Makola (MSc, Pretoria); James Short (MSc, Pretoria); Jaimie Whyte (MSc, Pretoria); Bianca Coulson (MSc, Pretoria); Obakeng Pule (CB MSc, UCT); Bruce Chrispo (CB MSc, UCT); Kim Daniels (CB MSC, UCT); Michelle Bouwer (CB MSc, UCT); Sean Morar (CB MSc, UCT); Martiné van den Berg (BSc Hons, UCT); Lara Strydom (M. Environ. Mgmt., Pretoria), Jochen Voges (BSc Hons, Pretoria)..

Research Assistants: James Crossley, Samantha Fourie, Stephan Horn, Amy Hunter, Justin Jacobs, Lesedi Moagi, Samantha Murphy, Lisa Nupen, Nick Smuts, Miqkayla Stofberg, Ansunel van Rooyen.