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The ‘Hot Birds Research Project’ (HBRP) is a large international research programme led from the Fitz, which integrates behavioural and physiological approaches to understand the impact of climate change on birds. The HBRP’s research has historically focused on birds in arid habitats in southern Africa, North America and Australia, but increasingly involves birds in mesic and humid environments – and in the subantarctic

In last year’s annual report, we shared the news that 2023 had been declared the hottest year since records began, and that temperatures were close to 1.5°C above pre-industrial averages. In 2024, the records were smashed again. On 10th January 2025, experts from the World Meteorological Association confirmed that global temperatures in 2024 exceeded the 1.5°C warming threshold for the first time. Extreme weather and climate-related impacts on lives and livelihoods are now a daily feature of the news cycle. 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, including a new project on the iconic seabirds of the Southern Ocean, in collaboration with the “Conserving Southern Ocean Seabirds” project (page 38). In addition, we continue to step up research on mitigation interventions and mechanistic modelling, and data collection on how behaviour and physiology inform climate change vulnerability and resilience of birds.

Temperature effects on behaviour – habitat, hydration and humidity
During 2024, the team continued long-running research building information across taxa on how birds respond behaviourally to the heat and the likely consequences for fitness. To date, HBRP work on this theme has encompassed 11 study species in arid, mesic, montane and urban environments of southern Africa and Australia. In 2024, Dr Shannon Conradie wrapped up her post-doctoral fieldwork on White-browed Sparrow-weavers Plocepasser mahali at Murray Guest Farm in the Kalahari. Shannon’s work focused on the relationships between air temperature and sparrow-weaver behaviour, body mass maintenance and hydration status. Shannon will use these data to validate state-dependent and biophysical models for this species, and to add to the growing comparative dataset.

Several other projects under this theme were also completed in 2024. Susie Cunningham and collaborator David Diez-Mendez from the Museo Nacional de Ciencias Naturales in Spain finally published work they carried out together in 2018 on incubation behaviour of Southern Fiscals Lanius collaris at Tswalu Kalahari, showing that the birds engage in egg shading behaviour during the heat of the day, buffering nest temperature from hot extremes. They also showed that nest temperature loggers are not an appropriate method for monitoring patterns of incubation in subtropical birds, because in hot environments nest temperature does not predictably drop during parental absences. The paper is published in the Journal of Arid Environments. James Short submitted his MSc thesis on behavioural responses of Karoo Chats Emarginata schlegelii to extremes of heat and cold in the Tankwa Karoo. James’ second chapter compared physiological heat tolerances of Large-billed Larks Galerida magnirostris from the Tankwa Karoo to those of other bird species in arid environments. James was awarded his degree with Distinction.

Finally, Ben Murphy wrapped up his PhD on how Fork-tailed Drongos Dicrurus adsimilis buffer costs of breeding in hot and arid environments, and will submit in February 2025. Ben’s PhD includes six field seasons’ worth of data, and was conducted through a time of drought, flood, pandemic and personal health crisis. Unlike any other species studied by the HBRP team to date, nestling growth and fledging size in Kalahari Fork-tailed Drongos is resilient to negative effects of hot weather. Ben discovered that drongo parents facilitate this remarkable feat by making multiple behavioural adjustments as temperatures rise, which collectively buffer their offspring against costs of high heatloads. For example, they increase provisioning rates in the mornings of hot days to buffer declines later in the day; and carry larger load sizes of prey to the nest per trip at times when temperature constrains the number of trips they can make. Furthermore, drongos shade their nestlings during hot weather, buffering nests from harmful temperature extremes. Drongo parents manage all this without measurable costs to their own body condition, perhaps because adjustments in provisioning behaviour also reduce heat loads experienced by adults. This suggests that behavioural compensation to overcome costs of hot weather for nestlings can also alleviate parent-offspring conflicts. Experimental work by Ben also uncovered that drongos will continue to forage to obtain water (from prey) under hot temperature conditions, but cease to forage if sufficiently hydrated, suggesting water rather than energy may be the more limiting resource during hot weather. Drongos’ ability to buffer their own and offsprings’ body condition in the heat appears related to their considerable behavioural flexibility. However, drongos also have the advantage of very low wing-loading and a flycatching lifestyle, meaning flight costs are lower and their foraging microhabitat (the air column) significantly cooler than those of other species which forage on the ground. Congratulations to Ben on finally completing this mammoth piece of work.

In 2024, we welcomed a new MSc student to this branch of the HBRP: Leslie Bayanza. Leslie is working in collaboration with the UCT Red-winged Starling Project to investigate whether high human presence buffers or exacerbates the impacts of hot weather on body condition and breeding success of the Upper Campus population of Red-winged Starlings Onychognathus morio at UCT. Further details of Leslie’s work are available in the Urban Birds section (page 45).

Carry over effects and cognition
Impacts of hot weather on nestling growth are almost ubiquitous among the species we have studied (except for drongos)! However, adverse conditions in early life can also have more subtle, long term consequences via impacts on less-visible components of development, such as cognition. In 2024, new MSc student Makgoshi began work to understand impacts of hot weather during development on problem-solving abilities of drongos. Her initial fieldwork in winter highlighted that juvenile drongos are much faster than adults to solve novel tasks including lifting lids on pots to extract mealworms. At the time of writing, Makgoshi is in the field assessing how capacity of birds to solve problems is affected by current and historic (i.e. experienced as a nestling) temperature exposure.

Heat-associated vocalisations in incubating estrildids
Post-doctoral fellow Dr Lisa Nupen joined the HBRP in 2024 to investigate heat-associated calls in estrildid finches as part of a collaboration between Andrew McKechnie and Dr Mylene Mariette of the Donaña Biological Station at Seville, Spain. In a 2016 paper in Science, Dr Mariette demonstrated how incubating female zebra finches Taeniopygia guttata communicate acoustically with their offspring prior to hatching via specific calls associated with hot weather. Lisa’s project seeks to determine whether similar heat-related vocalisations occur in southern African estrildid finches, including waxbills. During 2024, ethics and land-owner permissions were secured and Lisa conducted spatial analyses using SABAP data to prioritize study sites. After expert consultations and site visits, two locations on the Springbok Flats were selected. As of early 2025, Lisa has installed microphones at a number of blue waxbill nests and preliminary analyses suggest that heat-associated vocalisations may occur in this species, although further verification is needed.

Red-list species and mitigation interventions
In 2024, we continued research to understand how climate warming is affecting already-threatened species, and develop conservation mitigation tools.

CB MSc student Obakeng Pule completed work on the Southern Yellow-billed Hornbill Tockus leucomelas population at Kuruman River Reserve, experimentally assessing whether the impact of hot weather on nestling growth and nest success can be mitigated by provision of thermally-buffered nest boxes. Obakeng’s results suggest that nests in insulated boxes are more likely to succeed than those in uninsulated boxes. Nestlings in insulated boxes also weigh more than those in uninsulated boxes, throughout the entire growth curve. This suggests that nestbox insulation might be a cheap and effective way to improve breeding success under rising temperatures in nestbox-dependent species. Obakeng received a Distinction for his thesis and will graduate in 2025. We are continuing his experiment in the 2024/25 breeding season to understand how seasonal differences in environmental conditions may impact these results.

Another red-listed species that continues to be a focus for the HBRP is the Red Lark Calendulauda burra, a desert specialist restricted to sand dunes and gravel plains in South Africa’s arid west. A paper by Ryno Kemp and co-authors published during 2024 provided an up-to-date estimate of the population at one of the species’ strongholds, the Black Mountain Mine Conservation Area (BMMCA) near Aggeneys in the Northern Cape. Using a combination of habitat modelling, survey data and home range estimates based on telemetric tracking of Red Larks equipped with transmitters, the Red Lark population of the BMMCA was estimated at 232–382 individuals, considerably fewer than were thought to occur there three decades ago. Towards the end of 2024, University of Pretoria student Anton Schultz, spent three months at another site near Aggeneys investigating whether the Red Larks will make use of artificial shade if it is provided in their territories. The objective of Anton’s project is to evaluate whether artificial shade provision may be worth considering as a conservation intervention in light of rapidly advancing climate change and associated increases in air temperature.

Carrie Hickman has added a final breeding season of data collection for her PhD on Southern Ground-hornbills Bucorvus leadbeateri in summer 2024/25, to bring her sample size of nestlings close to 50. She has begun her writeup and has one chapter completed and three in advanced drafts. Her results show, among other things, that landscape temperatures experienced by hornbills are hotter in winter than summer on matched air temperature days due to low shade availability in winter, and that cooler riverine areas will become increasingly important thermal refuges in the lowveld landscape as the climate continues to warm. Carrie’s preliminary analyses also suggest impacts of hot weather on nestling growth especially during early development. Kyle-Mark Middleton rejoined the Southern Gound-hornbill team as a post-doctoral fellow in 2024, to further investigate the impacts of changing landscapes of heat on the birds’ behaviour, body condition, and interactions with other species. See page 36 for more details.

Wesley Gush’s PhD project on the implications of warming temperatures for Secretarybirds Saggitarius serpentarius continued in 2024, with a second field season of data collection on parental behaviour, nestling morphometrics and nest temperatures. Wesley worked hard with Marc Freeman and Bianca Coulson to develop a respirometry chamber large enough for Secretarybirds and will deploy this to measure thermal physiology of captive birds at Dullstroom in 2025.

Finally, research assistant Vanessa Stephen spent almost all of 2024 on subantarctic Marion Island, collecting data on thermoregulatory behaviours and landscape and microsite temperatures for surface-nesting seabirds including Northern and Southern Giant Petrels Macronectes halli and M. giganteus and Wandering Albatrosses Diomedea exulans. See page 38 for more information on this Hot Birds – Southern Ocean seabirds collaboration. .

Thermal physiology
The HBRP’s research on thermal physiology during 2024 focused on species inhabiting the Afromontane forests of the Magoebaskloof region in Limpopo province. PhD student Bianca Coulson and post-doctoral fellow Marc Freeman were based at a study site near Haenertsburg from October 2024 until early 2025, where they were joined for two months by visiting PhD student Ryan Leys from the University of Waterloo in Canada. One of the hypotheses Bianca is testing as part of her PhD is that birds inhabiting these forests show adaptive variation in evaporative cooling and heat tolerance correlated with vertical thermal gradients between the forest floor and the upper canopy. Bianca and Marc completed a tree climbing course in the run-up to the field season, which provided the training required for them to place temperature and humidity loggers at various heights in the forest to quantify temperature and humidity differences between the canopy, mid-stratum and the forest floor.

The team also caught birds inhabiting these different strata and measured their evaporative cooling capacity and heat tolerance, before releasing them. By the end of the season, they had collected data for around 20 species, providing the basis for comparing the thermal physiology of species occupying these different microclimates. The study species included inhabitants of the forest floor like Lemon Dove Aplopelia larvata, Orange Ground Thrush Geokichla gurneyi and Green Twinspot Mandingoa nitidula, mid-stratum species including Cape Batis Batis capensis, White-starred Robin Pogonocichla stellata and Blue-mantled Crested-flycatcher Trochocercus cyanomelas, as well as canopy-dwellers like Olive Woodpecker Dendropicos griseocephalus, Olive Bushshrike Chlorophoneus olivaceus and Southern Double-collared Sunbird Cinnyris chalybeus. One study species that proved particularly fascinating was the Narina Trogon Apaloderma narina. Not only did the trogons show extremely efficient evaporative cooling when experiencing humid heat, but they also appear to possess evaporative cooling behaviours not previously described among birds. In addition to the data needed to examine differences in thermal physiology correlated with microclimate, the team also began quantifying wet bulb temperature tolerance limits for a handful of species.

Thermal physiology publication highlights for 2024 included a 1) paper by Marc Freeman and co-authors in Ecology showing how humidity has shaped the evolution of evaporative cooling and heat tolerance in forest birds, 2) a paper on non-evaporative heat loss across the beaks of large forest hornbills by Bianca Coulson and co-authors, and 3) Jochen Voges’ meta-analysis of the functional role of metabolic suppression during avian thermoregulation in the heat. In addition, a paper led by Andrew McKechnie, in collaboration with colleagues at VulPro and the University of Pretoria’s Faculty of Veterinary Science, reported the results of a study exploring whether lead poisoning affects the ability of Pied Crows Corvus albus to thermoregulate during heat exposure. Published in Environmental Toxicology and Pharmacology, this is one of the first studies to explore interactions between environmental pollutants and the capacity of birds to keep cool during hot weather.

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 heat transfer between birds and their environment varies across landscapes, and the constraints that this places on birds’ ability to survive and reproduce. In 2024 Shannon Conradie continued work developing methods to validate and improve biophysical models of thermoregulation, energy and water balance of passerine birds under complex field conditions, using Southern Pied Babblers Turdoides bicolor and White-browed Sparrow-weavers Plocepasser mahali as study species. Shannon was also successful in attracting a prestigious Jennifer Ward Oppenheimer award for her research and joined Wits university as a lecturer in September!

Martiné van den Berg registered as an MSc student on a project validating biophysical models for thermal physiology and microclimates of Fynbos birds, with a view to predicting future physiological costs under changing temperatures and fire regimes in the Cape Floristic Region.

Hannah Glanville completed her Honours comparing biophysical model, black bulb, and taxidermic mount estimates of operative temperatures in arid savanna and urban environments, finding that the NicheMapR microclimate model produces more accurate predictions for natural than built-up environments. Hannah received a Distinction for her work .

Highlights:

  • The HBRP published 18 papers in international peer-reviewed journals in 2024.
  • Nicholas Pattinson graduated in September with his PhD on how temperature and resource availability shape thermoregulation and breeding outcomes in Southern Yellow-billed Hornbills.
  • Susie Cunningham published a chapter on behavioural responses of animals to climate change in new Oxford University Press book “Behaviour in a Changing World”, edited by Bob Wong and Ulrika Candolin.
  • Susie also presented two invited seminars at Monash University in Melbourne (as part of their Distinguished Women in Science seminar series) and at the Max Planck Institute for Animal Behaviour in Konstanz.
  • PhD students Linda van den Heever and Ryno Kemp graduated at the University of Pretoria’s autumn and spring ceremonies, respectively.
  • MSc students Bianca Coulson, Nazley Liddle, Obakeng Pule and James Short all received Distinction grades for their MSc theses.
  • Shannon Conradie was successful in her application for a permanent Lectureship at the University of the Witwatersrand, and was awarded the prestigious Jennifer Ward Oppenheimer Research Grant to kickstart her independent lab group.

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 2024
Team leaders and collaborators:
Prof. Andrew McKechnie (U. Pretoria / SANBI)
A/Prof. Susie Cunningham (FIAO, UCT)
Dr Janet Gardner (Australian National University)
Dr Alan Lee (BLSA / FIAO, UCT)
Dr Rowan Martin (FIAO, UCT)
Dr Ben Smit (Rhodes)
Prof. Vinny Naidoo (U. Pretoria)
Dr Melissa Whitecross (Conservation Alpha, Wits)
Dr Christiaan Brink (FIAO, UCT)
Dr Danielle Levesque (U. Maine)
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 Rita Covas (U. Porto / FIAO, UCT)
Dr Shannon Conradie (FIAO, UCT / Wits)
Dr Celiwe Ngcamphalala (BioSci, UCT)
Dr Chima Nwaogu (FIAO, UCT)
Dr Mia Momberg (U. Pretoria)
Dr Marc Freeman (U. Pretoria)
Dr Lisa Nupen (U. Pretoria)
Dr Amanda Bourne (Australian Wildlife Conservancy)
Dr Kyle-Mark Middleton (FIAO, UCT)

Students:
Carrie Hickman (PhD, UCT); Benjamin Murphy (PhD, UCT); Nicholas Pattinson (PhD, UCT); Bianca Coulson (PhD, Pretoria); Wesley Gush (PhD, Pretoria); Ryno Kemp (PhD, Pretoria); Leslie Bayanza (MSc, UCT); Martiné van den Berg (MSc, UCT); Nazley Liddle (MSc, Pretoria); Makgoshi Mogotsi (MSc, Pretoria); James Short (MSc, Pretoria); Jochen Voges (MSc, Pretoria); Jaimie Whyte (MSc, Pretoria); Lara Strydom (M. Environ. Mgmt., Pretoria); Obakeng Pule (CB MSc, UCT); Hannah Glanville (BSc Hons, UCT); Caitlin Read (BSc Hons, Pretoria), Ryan Leys (visiting PhD student, U. Waterloo).

Research Assistants:
Amy Hunter, Justin Jacobs, Bianca Koste, Lesedi Moagi, Samantha Murphy, Vanessa Stephen, Kiley van Meer.